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 
e 
Fic. 63.—Thorax of mutant stocks of Drosophila ampelophila. a, 
race ‘“without’’ trident; b, 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 
