Stretching out and closing the toes, she mixes the sticky mass with air and breaks the big bubbles up into smaller and smaller foam. Similar movements of the feet of the male drive the mass backward and leave the eggs more free for the fertilization that follows. When the eggs have been fertilized and provided with a protecting and aerating mass, the parents break out from the nest and take up their life amongst the trees. The foam mass meanwhile gradually becomes liquid, and flowing out through the hole the parents left on leaving the nest, carries the young into the outside water.
Very different is the nest made by another tree-frog in Brazil, The quaint, beaver-like activities of this creature (Hyla faber) are described by one who observed them in his own garden. On a moonlight night one may see a slight movement of the water as if something were moving under it. Then a little mud rises, shoved up by a tree-frog—but only the hands of this are visible. It dives down and again brings up mud;
gradually the accumulated mud seems a little wall, and eventually it rises 10 cm. above the water and extends as a ring a foot in diameter. Such atolls of mud are shown in Fig. 4. They form little circular dikes of mud elevated above the general expanse of water. The making of them is by no means a matter of chance. The frog—and it is the female that labors, in full enjoyment of her 'rights,' while the male rides passively—uses her hands to compress and to smooth the inside of the wall in a most remarkable way. The top also of the miniature fortress is carefully manipulated, the frog crawling out of the water to make all the structure solid and smooth, all but the outer escarpment, which is left rough.
The frog makes the bottom of the crater-like cavity, under water, smooth by gliding along it on its belly, and also by spreading out its hands over it. During all this work the frogs make no sound, though near at hand isolated males may be heard calling their mates.
In this circular nest the spawn is deposited, but not till four or