Page:Popular Science Monthly Volume 59.djvu/87

Rh is but little perfection of the senses as compared with the future adult stage. The experience gained as tadpole would seem to be of very little direct use to the frog when it begins its new life; it is chiefly the gain in material, the results of feeding, that makes the frog the better for its tadpole life. In the Surrinam toad this gain in size is provided for by the mother, who takes all labor off the shoulders of her offspring till they are toads like herself. Is there not an analogy between such habits and our own attitude towards the next generation? The child of the savage, or of the more unfortunate classes in 'civilized' communities, is put to getting its own livelihood at the earliest possible age; the favored child of the few is protected by the parental roof and fed with even university pabulum till nearly arrived at adult structure.

But the Surrinam toad is not the only one that is built mammallike, to carry its young within its own body; the group of pouched or marsujnal frogs of Venezuela have an even stranger contrivance for this purpose. Those who are fortunate enough to have access to a copy of Professor Davenport's profusely illustrated little volume, 'Introduction to Zoology,' will find a very attractive figure of one of these 'brooding tree-frogs,' taken from a water-color painting at Harvard College. On the middle of its back, above the loins, is a very large opening leading into the interior of the animal. This is the opening of a large brood-chamber. In one frog (Nototrema oviferum) this chamber continues forward on each side as two, even larger, chambers that reach almost to the head. The middle chamber is on the back, while the side chambers extend not only over the back, but down on the side, so as almost to meet one another across the belly. All these chambers lie just beneath the skin and are not deep, but flat, though they displace the viscera.

The walls of the chambers are very thick and vascular, except near the external opening, where the wall is of the same nature as the skin. The skin, in fact, seems to have grown in to line these chambers, but has been much changed in its character in those parts of the chambers that are remote from the openings. It is not known how this big bag grows over the body, nor whether it is always there, or only developed at the breeding season. These chambers are found in the female, and in some unknown way the eggs are transferred from the ovary into the pouches. As there is no internal opening to the pouch, the eggs must be laid as usual and then put upon the back, and so into the external opening of the brood pouch. Possibly the male aids in this function.

The eggs of this species are exceedingly large, being 1 cm. in diameter, more than eight times the bulk of a common frog's egg, and are also but few in number. In one case there were only four eggs in the outer, middle, chamber and eleven others m the two side chambers—fifteen eggs in all.