194 



MULTIPLE FACTORS 



be similarly explained, but also because the new 

 methods which have been developed in attacking it 

 are singularly adapted to the solution of such prob- 

 lems. The use of this method has been made pos- 

 sible by the information at hand as to the linkage 



Fig. 60. — Nwrnal wing (to left) and beaded wing (to right) of 



Drosophila. 



groups and as to non-crossing over in the male. 

 Without such knowledge the case would have been 

 practically insoluble. 



The same method of attack has also been used by 

 Dexter, in his experiments with the '^beaded" wing 

 of Drosophila (Fig. 60). The beaded character is a 

 variable one, some of the beaded individuals being 



