AMPHIBIA 379 



limbs in relation to the body come to overlie and obscure the 

 axial muscles proper. The Anura (frogs and toads) are espe- 

 cially adapted to leaping and swimming by the great muscular 

 development of the hind legs. 



405. Exercise. Are there any special advantages in the leaping habit of 

 motion either in the capture of prey or in escape from, enemies? Verify from be- 

 havior of toads and frogs. Can you find illustrations from other groups of animals ? 



406. Habits and Habitat. There are no marine Amphibia. 

 Nearly all live in or near the fresh-water streams, swamps, or 

 ponds, even in the adult stage. Some are good climbers (tree- 

 toads); others burrow. The tailless forms (Anura) are found 

 the world over. The Urodela belong chiefly to the northern 

 hemisphere. All are more abundant in warmer climates. Their 

 food consists largely of insects, worms, and the smaller animals. 

 The larvae even of carnivorous forms are sometimes vegetable 

 feeders. They may live for a long time without food, and sur- 

 vive the winter in the colder latitudes by burrowing deep into 

 the mud at the bottom of their ponds, or otherwise hibernating. 

 During this time the vital processes are suspended or much 

 reduced. 



407. Reproduction and Development. The common am- 

 phibia lay rather large eggs, with a considerable amount of yolk 

 which results in more or less unequal cleavage (Fig. 13, B). 

 The eggs are usually surrounded by a gelatinous material, for 

 their protection and adhesion, but they have no shell. They 

 are almost universally deposited in the water, where impreg- 

 nation takes place. In some of the Urodela impregnation is 

 internal. In occasional species the young are brought forth alive. 

 Ordinarily further development takes place in the water without 

 any attention from the parents (frogs and toads). In a small 

 South American frog (Rhinoderma) the male carries the fertilized 

 eggs in his vocal sacs until hatched ; in one of the tree-frogs from 

 South America the female has a pouch on the back in which 

 the eggs are stored and hatched ; in the Surinam toad the eggs are 

 placed by the male on the back of the brooding female, where 

 they become surrounded by spongy tissue. In these pits they 

 hatch at once into the adult form without having external gills. 



