66 THEORY OF EVOLUTION 



has also been found. Here the interesting 

 fact was discovered (Hoge) that duplication 

 takes place only in the cold. At ordinary tem- 

 peratures the legs are normal. 



In conti'ast to the last case, where a charac- 

 ter is doubled, is the next one in which the eyes 

 are lost (fig. 30) . This change also took place 

 at a single step. All the flies of this stock 



Fig. 30. Mutant race of fruit fly, called eyeless; a, a' normal 

 eye. 



however, cannot be said to be eyeless, since 

 many of them show pieces of the eye — ^indeed 

 the variation is so wide that the eye may even 

 appear like a normal eye unless carefully ex- 



