376 ZOOLOGY. 



from behavior of toads and frogs. Can you find illustrations from other 

 groups of animals? 



399. 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 survive the winter in the colder latitudes by burrow- 

 ing deep into the mud at the bottom of their ponds, or other- 

 wise hibernating. 



400. Reproduction and Development. The common 

 amphibia lay rather large eggs, with a considerable amount of 

 yolk which results in more or less unequal cleavage (Fig. n,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. Ordinarily further development takes place in the 

 water without any attention from the parents (frogs and 

 toads). In a small South American frog (Rhino derma) 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. This is of course a suc- 

 cessful adaptation (by eliminating the metamorphosis) to a 

 completely aerial habit. From this group we have beautiful 

 illustrations of unequal cleavage of the ovum, of which the 

 student should have the opportunity of seeing figures in more 



