THEORY OF EVOLUTION 



75 



F 2 



FIG. 36. Diagram illustrating a cross between a red eyed 

 male and white eyed female of the fruit fly (reciprocal cross 

 (of that shown in Fig. 35). 



It has been shown by Sturtevant that in a 

 wild species of Drosophila, viz., D. repleta, 

 two varieties of individuals exist, in one of 

 which the thorax has large splotches and in the 



