146 



ROSCOE R. HYDE 



had been brought about by selecting from those famiUes that 

 showed the least sterility (no. 17, table 9, and 17a, table 10). 



It seemed to me at first that the large number of sterile indi- 

 viduals that appeared in this stock might bear a causal relation 

 to the low productivity of the fertile pairs, but at the point in the 

 experiment when the sterile individuals were eliminated there was 

 no rise in productivity. I shall return to this question in the 

 second part of the paper. 



2. Sterility of the truncate stock 



TABLE 8 

 Sterility of the truhcate stock as it appeared in successive generations of inbreeding 



* Some doubtful cases are included. 



TABLE 9 

 Sterility of the truncate stock in F45 generation 



For the forty-seventh generation one pair was chosen from 17a. 

 It is to be noted that no sterile individuals had appeared in the 



