A Book of Natural History | Page 6

other animals; it cannot manufacture
the proteid materials of its body, but it has to take them ready made, or
in a condition which requires but very slight modification by devouring
the bodies either of other animals or of plants. The animal or vegetable
substances devoured are taken into the animal's stomach; they are there
digested or dissolved; and thus they are fitted to be distributed to all
parts of the fowl's own body, and applied to its maintenance and

growth.
The fowl's egg is formed in the body of the hen, and is, in fact, part of
her body inclosed in a shell and detached. It contains a minute rudiment
of a fowl; and when it is kept at a proper temperature by the hen's
sitting upon it, or otherwise for three weeks, this rudiment grows, or
develops, at the expense of the materials contained in the yolk and the
white, into a small bird, the chick, which is then hatched and grows into
a fowl. The animal, therefore, is produced by the development of a
germ in the same way as the plant; and, in this respect, all plants and all
animals agree with one another, and differ from all mineral matter.
Thus there is a very broad distinction between mineral matter and
living matter. The elements of living matter are identical with those of
mineral bodies; and the fundamental laws of matter and motion apply
as much to living matter as to mineral matter; but every living body is,
as it were, a complicated piece of mechanism which "goes," or lives,
only under certain conditions. The germ contained in the fowl's egg
requires nothing but a supply of warmth, within certain narrow limits of
temperature, to build the molecules of the egg into the body of the
chick. And the process of development of the egg, like that of the seed,
is neither more nor less mysterious than that, in virtue of which, the
molecules of water, when it is cooled down to the freezing-point, build
themselves up into regular crystals.
The further study of living bodies leads to the province of biology, of
which there are two great divisions--botany, which deals with plants,
and zoölogy, which treats of animals.
Each of these divisions has its subdivisions--such as morphology,
which treats of the form, structure, and development of living beings,
and physiology, which explains their actions or functions, besides
others.
[Illustration]

LIFE GROWTH;--FROGS
(FROM A SONG OF LIFE.)
BY MARGARET WARNER MORLEY.[1]
[1] Copyright by A. C. McClurg & Co., 1891.
[Illustration]
Somewhat higher than the fish in the scale of life is the frog. Although
he begins life as a fish, and in the tadpole state breathes by gills, he
soon discards the water-diluted air of the pond, and with perfect lungs
boldly inhales the pure air of the upper world. His life as a tadpole,
although so fish-like, is much inferior to true fish life: for though the
fish has not the perfect lung, he has a modification of it which he fills
with air, not for breathing purposes, but as an air-sac to make him float
like a bubble in the water. Will he rise to the surface? he inflates the
air-bladder. Will he sink to the bottom? he compresses the air-bladder.
But in the frog the air-bladder changes into the lungs, and is never the
delicate balloon which floats the fish in aqueous space. When the frog's
lungs are perfected, his gills close, and he forever abandons fish-life,
though being a cold-blooded creature he needs comparatively little air,
and delights to return to his childhood's home in the bottom of the pond.
But although he can stay under water for a long time, he is obliged to
hold his breath while there, and when he would breathe must come to
the surface to do so. It is possible to drown him by holding him under
water.
[Illustration: A FROG.]
As a feeder the frog relies upon animal life, which he expertly seizes
with a tongue fastened by the wrong end, as compared with our tongues.
He is a certain marksman, and when he aims at an insect the chances
are that the insect will enter his stomach and be there speedily changed
into a new form of animal life.
Although from the moment the gills disappear the frog is a true land

animal, he is obliged, on account of the fish-like character of his young,
to lay his eggs in the water. For this purpose the frogs enter the pools in
early spring. The surface of every country pond swarms with the
bright-eyed little creatures. They have awakened from a long, cold,
winter sleep, to find the spring about them and within them. Life has
suddenly become abundant and joyous. Their sluggish blood flows
faster, their