Page:Popular Science Monthly Volume 59.djvu/80

70 the water; and the young remain within the egg until they are complete frogs in shape. While passing through so much of their life-history within the egg shell, the young manage to breathe, not by their tails, but by special folds of skin that grow out on either side of the belly, in rows, as shown in Fig. 1. The young frog also makes a temporary contrivance for breaking through the egg shell, something like the horn on the beak of a hatching chick or the protuberance used by many reptiles for the same purpose. This peculiar little organ in the frog is shown in Fig. 1 and again in Fig. 2, where it adds a decided retroussé element to a not too intellectual countenance.

We might place frogs in three groups: those that are simply layers, those that are nest-makers, and those that are nurses.

As a nest builder we may reckon the Cystignathus mystaceus of Brazil. This frog makes a hole about as big as a teacup under stones or decayed logs near enough to puddles of water to be covered by water when the pond rises after heavy rains. In this nest the yellow eggs are laid in a mass of thick, white foam, very like beaten white of egg in appearance. The eggs hatch into tailed tadpoles, and, when the water rises over the nest, these young swim off like our common tadpoles. They differ, however, in being able to overtide dry seasons. When the pond dries up and common tadpoles would die, these peculiar creatures gather under boards or logs and there keep moist—apparently by the aid of an unusual amount of material secreted by their skins. Evidently the habits of this frog are nicely adjusted to the climatic conditions under which it lives.

A tree-frog of West Africa (Chiromantis rufescens) lays its eggs in leaves of trees in a mass of foamy material that, on drying, hardens on the outside, but becomes liquid within, and so lets the tadpoles swim about for a while till a rain washes them off the tree into the water. While living the short part of its tadpole stage in the nest made by the mother for it, the tadpole has gills such as our common tadpoles breathe with, as well as a tail to swim with. In this aerial existence the young have the protection not only of the surrounding foam, but often of leaves that are sometimes stuck to it. This perfecting of the nest by the use of leaves to envelop the foam mass becomes the rule in two sorts of frog in Brazil (Phyllomedusa Jheringii and Hyla nebulosa). The former puts its big white eggs into a mass 40-50 mm. long and 15-20 wide, enveloped by two or three leaves, sometimes willow tree leaves, in such a way that they make a tight case open at one end. The young seem to be so fitted for this peculiar {{hws|wet-ham|wet-hammock}