MULTIPLE FACTORS 207 



because selection had changed the potency of the 

 trident factor, were it not that during these three 

 years over 100 other mutant characters had appeared 

 in Drosophila, affecting every part of the body. Ob- 

 viously when such changes are taking place every- 

 where, one would almost certainly find changes 

 occurring in the parts that were being carefully 

 scrutinized for any changes whatever. 



