THE ADDrnON OF DETAILS 



91 



Stages, so that their life-history is very complicated. 

 These larval stages often represent ancestors in the 

 evolution of the animals. For instance, frogs were 

 evolved from ancestors which lived in water, and 



Fig. 24. — Part of a caterpillar v/ith the skin dissected away 

 to show the buds from which the butterfly's wings will arise 



they still have a water-living larval stage, the tad- 

 pole. The Ascidians, which we mentioned before as 

 examples of animals with mosaic eggs, are not so 

 well known as frogs, but they also have a larval stage, 

 which is rather like a tadpole. Here the meta- 

 morphosis by which the larvae turn into the adult is 

 much more radical, although the adults remain 



