148 



KOSCOE R. HYDE 



the same strain on inbreeding may behave differently in successive 

 generations as has been shown in the history of the inbred and 

 truncate stocks. An additional difficulty is met in finding a highly 

 fertile strain against which to test a known sterile strain. In the 

 face of these difficulties a number of detailed experiments have 

 been required in order to determine (1) the method of transmission 

 of the female sterility, and (2) the relation between low production 

 and sterility in the truncate stock. I shall present first the evi- 

 dence that bears directly on the method of transmission of female 

 sterility. 



T.\BLE 12 

 Sterility as it appeared in the Woods Hole stock 



STERILE 



March 2, 1912 

 June 24, 1912. 

 July 10, 1912., 



A wild stock to which I shall refer as the Woods Hole stock was 

 characterized by the presence of but few sterile individuals. 

 Consequently this was good material against which to test the 

 sterility of the inbred stock. An entirely fertile stock would be 

 the ideal one to use but it is the experience of all who have bred 

 these flies that a sterile pair is occasionally met without any assign- 

 able cause. Table 12 gives the history of the fertile Woods 

 Hole stock. 



At the time the following cross was made there appeared in the 

 Woods Hole stock that was used as a control by placing under 

 similar conditions, 4 out of 70 pairs that were sterile. There 

 were 2 sterile males and 2 sterile females (table 12, Lot B). In 

 order to determine the behavior of the sterility in the Fi and F2 

 generations, the inbred females were paired with the Woods Hole 

 males. The reciprocal cross was also made. The offspring that 

 resulted from this cross were paired together, brothers and sisters, 

 for the Fi generation. The grandchildren were paired for the 

 Fo generation. The offspring from three families of the inbred 



