LETHAL FACTOES IN DROSOPHILA 



535 



TABLE 5 

 13, 1 



.13, 



Two high to 9 low ratios appear in 13, 7, which probably in- 

 dicates a lethal as the parent also had a high ratio (viz., 2.7 : 1). 



These four tests of 13 show beyond doubt that a lethal was 

 present, since each of the four families tested gave some high 

 ratios. 



