12 THEORY OF EVOLUTION 



their size; each originated independently from 

 the wild type. 



The wings of the wild fly are straight (fig. 

 4). Several types have arisen in which the 

 wings are bent upwards and in the most ex- 

 treme type the wings are curled over the back, 

 as seen in figure 55 (g) , yet there is no histori- 

 cal connection between these stages. 



Mutations have occurred involving the pig- 

 mentation of the body and wings. The head 

 and thorax of the wild Drosophila ampelophila 

 are grayish yellow, the abdomen is banded with 

 yellow and black, and the wings are gray. 

 There have appeared in our cultures several 

 kinds of darker types ranging to almost black 

 flies (fig. 20) and to lighter types that are 

 quite yellow. If put in line a series may be 

 made from the darkest flies at one end to the 

 light yellow flies at the other. These types, with 

 the fluctuations that occur within each type, 

 furnish a complete series of gradations; yet 

 historically they have arisen independently of 

 each other. 



Many changes in eye color have appeared. 

 As many as thirty or more races differing in eye 



