THEORY OF INVOLUTION 



Fig. 3(). DiagrEiin illustrating a cross between a red eyed 

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

 (of that shown in Fig. 3.5). 



It lia.s been .shown b}^ Stnrtevant tliat in a 

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

 two varieties of individuals exist, in one of 

 which the tliorax has large splotches and in the 



