[1] See “The Story-Book of Science.” [↑]
CHAPTER XXXV
THE BATRACHIANS
American Tree Toad
“I have kept until the last the ugliest and the least esteemed of our helpers, the toad. With it must be classed the frog and the tree-toad because of their close resemblance to it in form and, still more, because of the similar change all three undergo in developing from the egg to the full-grown animal. Common language gives the name of reptile, from a Latin word meaning to creep or crawl, to the snake and the toad, the lizard and the frog, and all similar hairless animals having either no legs at all or very short ones and crawling on the stomach. Science, however, makes a difference; it limits the name reptile to the snake, the lizard, and other animals having a scaly skin and hatching from the egg in the form they are to keep; and it gives the name batrachian (from the Greek batrachos, a frog) to the toad, frog, tree-toad, and some others, which [[274]]have a naked skin and whose first shape gives place later to a different one. Reptiles do not undergo a complete change; batrachians do. Just as the butterfly is first a caterpillar, quite different in structure, its way of living, and its diet from what it finally becomes in its perfect state, so the toad, the frog, and the tree-toad begin their existence as tadpoles with none of the structure and habits they are finally to have.
“Tadpole or big-head, that is the word to indicate the batrachian in its transitory state. A very large head merging into a plump stomach that ends abruptly in a flat tail—such is the animal in the beginning. It has no limbs, no organs of locomotion unless it be the tail, which whips the water to push the creature forward and serves as oar and rudder at the same time. The toad tadpole is small and entirely black; the frog tadpole is much larger, silvery on the belly and grayish on the back. All tadpoles inhabit still waters, as ponds or pools warmed by the sun; but for toad tadpoles even shallow puddles or wagon-ruts with a few inches of rain will suffice, where they can gather in black rows or stretch themselves flat on the stomach in the tepid mud at the water’s edge. Frog tadpoles, however, thrive best in ponds of some extent, with various water-plants and sufficient depth for diving and swimming. Like fish, tadpoles breathe the air that is in water; and like them, also, they die if kept out of water a short time. Thus they are real fish as far as breathing is concerned. But in their final form batrachians [[275]]breathe atmospheric air and die of suffocation in water. They are land animals in that state, and breathe like other land animals.
“You have very often seen frogs and toads in the water, and no doubt you think they could live there indefinitely. Undeceive yourselves: they go to the water only to lay their eggs or to escape from some danger or to bathe in hot weather, but they could not remain under water any length of time without dying. They have to come up at intervals to breathe, which they do by getting at least the nostrils out. Here we have a difference between the tadpole and the full-grown batrachian, between the larva, so to speak, and the creature at its maturity: the tadpole lives in water and perishes in the air, whereas the frog that comes from it lives in the air and perishes in water.