260 



MULTIPLE FACTORS 



mutant characters had appeared in Drosophila, 

 affecting every part of the body. Obviously when 

 such changes are taking place everywhere, one 

 would almost certainly find changes occurring in 



a 





d 



V. 



Fig. 63. — Thorax of mutant .stocks of Drosophila ampelophila. a, 

 race "without-" trident; 6, race "with" trident; c, race called streak; 

 d, race called trefoil; e, race called band. 



the parts that were being carefully scrutinized for 

 any changes whatever. 



Zeleny, in the course of a long series of selections 

 for narrower and wider bar eye, found such mu- 

 tations in both the plus and the minus direction. 

 He determined that they took place in the chief 

 factor for bar eye itself, thus establishing a series of 



