180 FIRST LEIS80N8 IN ZOOLOGY. 



groups, in grass which grows up and rests on the water. 

 The tadpoles hatch in two days. In a week after the tad- 

 poles appear the gills are absorbed. Meanwhile the tad- 

 poles hang by their "holders/' or suckers on the lips, to 

 the leaves, as seen in the engraving. When about three 

 weeks old the hind legs begin to bud out in front of the 

 base of the tail. During the eighth week they take little 

 food ; the four legs grow out, the tail disappears, the mouth 

 becomes adapted for seizing and eating insects, and they 

 leave the water. This tree-toad depends for safety on its 

 power of changing its color from green to gray; it hides 

 among leaves, or in crevices in the bark of trees, when 

 it becomes like an excrescence on the bark of the tree. 



We have noted the metamorphoses of the jelly-fish, the 

 starfish, the butterfly, and that of the frog or toad is no 

 less remarkable. The tadpole is, so to speak, an entirely 

 different animal from the adult. It is even lower in the 

 scale than a fish ; it has neither fins nor legs ; like a young 

 shark, it breathes by external gills. The mouth is very 

 small (Fig. 188, A), with no tongue and the horny toothless 

 jaws only enable it to nibble decaying leaves, etc. The 

 digestive canal is remarkably long and coiled in a close 

 spiral, while in the carnivorous adult it is much shorter, 

 with few turns. The vertebrse of the tadpole are biconcave, 

 as in fishes, afterwards becoming converted into cup-and- 

 ball joints. 



We thus see that during the changes from the tadpole 

 to the frog or toad the body is, so to speak, made over 

 anew, both within and without, and that the creature, as 

 tadpole and frog, leads two lives, — one fish-like in the water, 

 feeding on decaying vegetable and animal matter ; the other 

 as an active, leaping, tailless, air-breathing creature, feeding 

 on smaller animals. 



Eeviewing the essential characters of the fishes and am- 

 phibians, we see that they have many in common, and that 

 they should be associated together ; while, as we shall see 

 farther on, the reptiles and birds are intimately allied. 



