It is very interesting in the spring to watch the gradual development of a frog from the egg, through the tadpole stage of its existence, till at last it assumes its final form.
The old frogs emerge from their winter hiding-places in the mud, early in the spring, and during April their eggs may be found floating on almost every stagnant pond.
A group of these eggs in their early stages of development looks like a mass of clear white jelly, containing numbers of black specks, each of which is really the germ of the future tadpole.
In order to watch the development, a group of the eggs should be taken and put in a shallow vessel of water, which, if kept in the house, should have a bell-glass, or some other covering, over it, to keep out the dust.
The jelly-like mass which envelopes the future tadpole is so clear that all its changes can be easily watched.
First the head appears, then a flat tail, and in course of time the nostrils, mouth and large eyes, till at length the completed tadpole bursts open its gelatinous covering, and apparently not in the least embarrassed by its new surroundings, begins swimming briskly about, looking for something to eat.
The time occupied in hatching varies in different countries, according to the climate, from four days to a month.
The following stages are even more interesting, especially for those who can take advantage of the transparency of the parts to watch the circulation of the blood through a microscope.
The body of the tadpole gradually gets broader, while the tail gets thinner and thinner, till it finally disappears altogether; but before that happens, its place has been taken by two hind legs, which first appear under the skin and then gradually push their way through.