Page:Popular Science Monthly Volume 59.djvu/83

Rh five days, as a rule, after the nest is completed; there is a period of rest between the nest-making (which in one case required two successive nights) and the egg-laying. The young hatch out as tadpoles and continue to live in the narrow circle of home till the wall be broken down by time and weather to set them free in the world.

It is the habit of all these nest-makers to put their eggs into more or less imperfect nests and then go off and leave them to their fate, the nest, no doubt, increasing the chances of the young passing safely through the earliest stages of infancy—which we all know is a critical period for man or fish. Some other frogs have quite a different habit; carrying their eggs about with them, and so giving them the benefit, if not of actual defense against enemies, at least of passive protection, in that the eggs thus have the same conditions of moisture and concealment which they, the adults, need and obtain for themselves. Such frogs we have called 'nurses.'

Of these nurses the most often mentioned is the so-called 'obstetrical toad' found in Switzerland, France and western parts of Germany. As shown in Fig. 5, the eggs are carried about attached to a band, which is wrapped about the legs of its parent, but the parent who thus carries the offspring about in the moist grass as it seeks food in the evening is not, as one might expect, the mother, but the father toad.

When the eggs are laid and fertilized, the male takes up his burden and carries it till the young are ready to hatch, when he goes to the water and lets the brood escape into the proper element. What leads him there at the right time remains still to be found out. How he comes to assume this care is also not clear; according to some accounts the male, when upon the back of the female, seizes the egg-string first with the right, then with the left foot, and wraps it in figure of eight loops about its own legs. Others say that the male sits behind the female, with its back turned toward her, and as the eggs emerge, the male seizes them between his ankles and, throwing himself now on his back and now on his belly, turns over and over until the egg-string is all drawn out and wrapped about his legs; hence the name Alytes