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 contrast 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- 



