296 . ELEMENTARY ZOOLOGY 



and the gills disappear (except in the cases of the few forms 

 which retain gills through life). The tail shortens and 

 finally disappears in the frogs and toads ; with the salaman- 

 ders the tail-fin only is lost. At the same time the change 

 from water to land is made. Further growth is very 



FIG. 120. Tadpoles. (Photograph from life by Cherry Kearton; per- 

 mission of Cassel & Co.) 



slow; frogs are not really adult, that is, capable of pro- 

 ducing young, until they are five years old, and they may 

 continue to increase in size until they are ten years old. 



The food of the adult batrachians is almost exclusively 

 small animals, particularly insects and worms. Crus- 

 taceans, snails, and young fish are also eaten. The tad- 

 poles also eat vegetable matter. Almost all batrachians 

 are nocturnal in habit, remaining concealed by day. In 

 the zones in which cold winters occur they hibernate or 

 pass the winter in a torpid condition, or state of " sus- 

 pended animation," or, as it is said, they sleep through 

 the winter. Frogs burrow into the mud at the bottom of 

 ponds at the approach of winter and come forth early in 



