12 THEORY OF EVOLUTION 



their size; eacli originated independently from 

 the wild type. 



The wings of the w^ld 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 .5.5 (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 Ijlack, 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 tlie darkest flies at one end to the 

 light yellow flies at tlie otlier. These types, with 

 the fluctuations that occiu* witliin each type, 

 furnish a complete series of gradations; yet 

 historically they liave arisen independently of 

 eacli other. 



jNIany changes in eye color have appeared. 

 As many as tliirtv or more races differino; in eve 



