THEORY OF EVOLUTION 71 



fects as well. The females are almost com- 

 pletely sterile, while the males are fertile. The 

 viability of the stock is poor. When flies with 

 rudimentary wings are put into competition 



FIG. 34. Mutant race of fruit fly, called rudimentary. 



with wild flies relatively few of the rudimentary 

 flies come through, especially if the culture is 

 crowded. The hind legs are also shortened. 

 All of these effects are the results of a single 

 factor-difference. 



One may venture the guess that some of the 

 specific and varietal differences that are char- 



