AMPHIBIANS
You will remember that the amphibians are distinguished from the true
reptiles by having to pass through a tadpole stage before they obtain
their perfect form. A good example is the frog, which in one kind or
another exists in all parts of the earth except the very coldest. No
doubt, you have often seen great masses of its jelly-like spawn floating
on the surface of ponds early in the spring; and you must have wondered
how such small creatures as frogs could possibly lay such enormous
batches of eggs.
But the fact is that when these eggs are first laid they are very tiny.
Each egg is only about as big as a small pin's head. Instead of having
shells, however, they are covered with a very elastic skin, while at the
same time they soak up water. So, as soon as they pass into the pond
they begin to swell, and very soon each egg is as big as a good-sized
pea.
TADPOLE AND FROG
In the middle of each egg is a round black spot, which increases in size
every day. This is the future tadpole, and after a time the egg-skin
splits, and out it tumbles into the water.
It is an odd-looking creature--just a big round head with a tiny pair of
gills and a little wavy tail, and nothing else at all. But it manages to
swim by wagging its tail, and it feeds on the tiny scraps of decaying
matter which are always floating about in the water of the pond. Before
long a little pair of legs begin to show themselves just at the base of
the tail. A few days later another pair begin to grow in front of them.
Then, by slow degrees, the tail passes back into the substance of the
body, and so do the gills, while lungs are developed and nostrils are
opened. And by the time that all these changes have taken place the
tadpole has ceased to be a tadpole and has turned into a frog.
It leaves the water now and lives upon land, feeding upon small insects,
which it catches in a most curious way. Its tongue is turned, as it
were, the wrong way round; for the root is just inside the lips, while
the tip is down the throat. Besides this, the tongue is very elastic and
very sticky. So the animal catches its victims just as the chameleon
does, flicking out its tongue at them and just touching them with the
tip, to which they adhere. And as the tongue is drawn back into the
mouth it pokes them down the throat; so that frogs do not even have to
take the trouble of swallowing their dinner.
If you look at a frog's hind feet, you will notice that the toes are
joined together by webbing. This allows them to be used in the water as
well as upon dry land. It is generally said that frogs swim. But if you
watch them in the water you will see at once that they do not really
swim at all, but leap along, just as they leap along the ground. And
each leap carries them through the water for some little distance.
TOADS
In some ways toads are like frogs; but you can tell them at once by
their rough, dry skins, which are covered with warts like glands. And
they crawl over the ground, instead of leaping as frogs do. They are
very common almost everywhere, and you may often find them hiding under
logs or large stones during the daytime.
Toads do not lay their eggs in great masses, as frogs do, but arrange
them in strings about four feet long and an eighth of an inch wide. Each
of these strings consists of two rows of eggs fastened side by side
together. The tadpoles are very much like those of the frog, the chief
difference being that they are rather smaller and blacker.
NEWTS
All through their lives newts keep their tails, instead of losing them
when they cease to be tadpoles.
You can find newts in plenty all through spring and summer by
fishing with a small net in any weedy pond; but you will find that they
are not all alike. Some have wavy crests running all along their backs;
others have none; and some are brightly colored while others are plain
olive green all over. Often in the woods in certain parts of the United
States you will meet with little newts traveling about on the damp old
leaves; and they are very conspicuous because of their brilliant
vermilion color. These are young green newts which come out of the
water, live ashore for a year or so in the red suit, and then go back to
the water and a green coat.
Newts lay their eggs in a very curious manner. They do not fasten them
together in great batches, like the frog, or in long, narrow strings,
like the toad. They lay them one by one. And the mother newt takes each
egg as she lays it, places it in the middle of the narrow leaf of some
water-plant, and then twists the leaf neatly round it with her little
fore feet, so as to wrap it up in a kind of parcel! The tadpole which
hatches out of this egg is very much like that of a toad or a frog; but
the front legs are the first to appear, instead of the hind legs, while
the tail, of course, does not pass back into the substance of the body.
Newts swim with their tails, and very pretty and graceful they look as
they move through the water. When they cease to be tadpoles, of course,
they breathe air, just as toads and frogs do, and have to come up to the
surface every two or three minutes to obtain it. And as long as they
live in the pond they feed upon grubs and worms and tiny water-insects.
SALAMANDERS
The curious creatures known as salamanders are related to the newts, and
begin their lives in just the same way. But after they have ceased to be
tadpoles they only visit the water for two or three weeks in the spring.
The most celebrated member of this group is the spotted salamander,
which is found in Central and Southern Europe, and also in Algeria and
Syria. When fully grown it is about eight inches long, and may be known
at once by the two rows of large yellow blotches which run down from
the back of its head, right along its body, to the very tip of its tail.
In days of old it was thought that the salamander had the power of
walking through fire without being burnt! And it was also supposed, if
it were attacked, to spring upon its enemy, bite out a piece of his
flesh, and then spit fire into the wound! As a matter of fact it is
almost harmless, and may be picked up and handled without the slightest
danger. But the glands on its skin, like those on the toad's head and
back, contain a rather poisonous fluid, which is squirted out if they
are squeezed. So that if a dog were to pick up a salamander he would be
quite sure to drop it again very quickly, and would most likely foam at
the mouth for some little time.
Salamanders are very slow and timid creatures, and generally spend the
whole of the day concealed in some crevice, or in the hollow trunk of a
tree, or perhaps under a large stone. They feed upon slugs and small
insects.
There are several kinds in North America, some of which, as the
hellbender, are a foot or more in length.
The giant salamander, which is sometimes nearly a yard long, is found in
the rivers of China and Japan, and spends the whole of its life in the
water. It feeds chiefly upon fishes.
THE AXOLOTL
This is one of the most singular of all the amphibians. It is found in
North America. Sometimes it develops into its perfect form, and
sometimes it remains a tadpole all its life, and yet lays eggs just as
though it were adult!
In the lakes of the southern Rocky Mountains the life of this creature
is just like that of any other batrachian. That is, it is hatched out of
the egg as a tadpole, grows first one pair of legs and then another,
loses its gills by degrees, and at last appears in a lizard-like form,
leaving the water and living upon dry land. But in the lake which
surrounds the city of Mexico it never becomes anything more than a big
tadpole, keeps its gills throughout its life, and does not leave the
water at all.
THE OLM
The olm, or proteus, is found only in the underground lakes of Carniola
and one or two other parts of Central Europe. It is about a foot long
when fully grown, and has a slender, snake-like body, with a pair of
tiny legs just behind the head, and another pair at the base of the
tail. It is perfectly blind, the eyes being hidden under the skin, and
yet cannot bear light. For if it is kept in captivity it will always
hide in the darkest corner that it can find. And it has been known to
live in confinement for five years without once taking any food.
What the habits of this extraordinary animal are in nature no one knows,
as it has never been found except in these underground lakes.
In color the olm is pinkish gray, with bright-red gills, and there are
from twenty-four to twenty-seven grooves upon either side of its body.
FISHES