MULTIPLE FACTORS 



247 



knowledge the case would have been practically 

 insoluble. 



Similar methods of attack have also been used 

 by Dexter, and by MuUer, in their experiments 

 with the ''beaded" wing of Drosophila (Fig. 60). 



Fig. 60.— Normal wing (to loft) and beaded wing (to right) of 



Drosophila. 



The beaded character hkewise is a variable one, 

 some of the beaded individuals being very nearly 

 normal in appearance. The degree of abnormality 

 and the proportion of abnormal offsjiring are both 

 capable of being altered, within limits, by selection 

 or by crossing to normal stock. 



Dexter crossed beaded flies to flics carrying 



