THE LIVING WORLD 



233 



live in, but birds are, as before said, very hot-blooded, 

 their warmth being promoted by the fact that air passes 

 from their lungs into different parts of their bodies, 

 sometimes even into the substance of almost all their 

 bones. 



Frogs and toads are animals which, in their young 



FIG. 47. 



4 



THE DEVELOPMENT OF THE FROG FROM THE TADPOLE. 



4 and 5 show the limbs growing out : 6 and 7 the tail very nearly 

 and quite absorbed. 



condition, possess a power which has not yet been 

 noticed. Their young, called tadpoles, are aquatic and 

 do not at first breathe at all by lungs, but by the inter- 

 vention of delicate processes of skin which are placed on 

 either side of the neck and which float in the water, 



