ROUGHOID. 



35 



ru se ru se 



X <7 



ru se 



July 24, 1919. 



ru + 



ru se 



X c? 



+ se 



ru se 



May 24, 1919. 



The total of these cultures (1,356 flies) shows the cross-over 

 value for roughoid and sepia to be 25.3. 



Again, a dichaete female (known to be heterozygous for rough- 

 oid) was backcrossed to a roughoid male from stock. From 

 that experiment, I found the cross-over value for roughoid and 

 dichsete to be 35.9, as follows: 



ru 



D 



ru 



X c? 



ru 



July 10, 1919. 



This indicates that roughoid is situated to the left of sepia, 

 since the normal distance between sepia and dichaete is known to 

 be about 11.7 units. 



