LIFE HISTORY OF THE FROG 



287 



Life history of the frog. The little tadpole then hatches from 

 the gelatinous egg. For the first two or three days, it remains 

 attached to grass by 

 a sucker-like mouth. 

 Then it begins to 

 feed on algae and 

 other vegetable 

 matter. When first 

 hatched, it has e.v- 

 ternal gills, which 

 grow out into long, 

 branching tufts. 

 Later, four pairs of 

 internal gills are 

 formed and the ex- 

 ternal gills are ab- 

 sorbed. The hind 

 limbs soon appear ; 

 later, the fore limbs 

 develop. The tail 

 then decreases in size 

 and is gradually ab- 

 sorbed. The gills, 

 too, are absorbed, 

 and lungs are formed 

 to take their place. 

 The two-chambered 

 heart of the tadpole becomes the three-chambered heart of the frog. 

 Finally the form resembling that of the adult frog is acquired. 



Reproduction of other animals. The reproduction of all higher 

 animals is similar to the reproduction of the frog. All females 

 have ovaries producing eggs, and males have spermaries or testes 

 producing sperms. The sperms fertilize the eggs and thereby 



N. Y. Zoological Hoc. 



The frog first hatches from the egg in the form of a tadpole. 

 Gradual changes take place which transform it into the adult 

 frog. This change of body form is called metamorphosis. 



