30 WHAT EVOLUTION IS 



Frogs, for instance, lay eggs and 

 from these are hatched, not frogs, 

 but tadpoles which eventually, through 

 a series of rather complicated bodily 

 changes, reach the condition of an 

 adult frog. 



The remarkable peculiarity of this 

 kind of growth is that, during the 

 steps in its progress, the young ani- 

 mal often shows striking resem- 

 blances to other animals. Thus, in 

 the instance just given, the tadpole of 

 the frog has unquestionably fish-like 

 characteristics. Instead of having 

 front and hind legs for locomotion as 

 in the adult frog, the tadpole moves 

 about by means of a flattened tail in 

 a way similar to that of a fish. More- 

 over, the tadpole has in its neck a 

 system of gills by which it breathes 

 precisely as a fish does. As develop- 

 ment goes on, these gills are gradu- 

 ally absorbed and are replaced by 



