170 THKORY OF E^'OIA"^IO^' 



as Dexter has shown, tliat a nuniher of mutant 

 factors that act as mochtiers liave been picked 



l^'id, 8-k Two flies showing l)o:i(leil wings. 



11]) in the course of the selection, and when it 

 is recalled that during those five years over 

 12.5 new cliaracters liave apj^^'^red elsewhere 

 it does not seem improbable that factors also 

 have appeared that modify the wings of this 

 stock. 



(8) The third method is one that has been 

 developed principally by East for plants; also 

 1)V 3IacD<jwell for rabl)its and Hies. The 



