168 ROSCOE R. HYDE 



should be low producers. This would seem to correspond to 

 Castle's results but in my case we meet with a difficulty at the 

 outset on such an assumption for it appears that the egg-laying 

 power of the affected female is totally abrogated. My evidence 

 will not deny the possibility of transitional stages but it is not clear 

 how an egg-laying mechanism should be able to expel a few eggs 

 and not all. 



Critical evidence is hard to obtain on this point because low 

 production may be due to a variety of causes. Attention is 

 called to the truncates, in which there was no rise in productivity 

 as the sterile individuals were practically eliminated. 



The history of the inbred stock allows us to form a more reliable 

 opinion, for the total output of offspring at first was much greater. 

 In table 2, Part 2, we get results that look as though the produc- 

 tivity is running down as the sterile females appear. The table, 

 however, does not convey all the facts of the experiment, for in 

 the Fe generation where 65 offspring is recorded as the average 

 per pair, some of the flies failed to emerge from the pupae. The 

 generations which precede and follow show more nearly the actual 

 facts in the case, namely, a gradual decrease in productivity. 

 That this was a high producing strain in the beginning of the ex- 

 periment there can be no doubt; for in the second generation the 

 average for sixteen pairs is 365 offspring. The low production in 

 the first generation is probably due to inexperience in handling, as 

 half of the females were dead at the end of two weeks. The pro- 

 duction gradually fell despite the fact that facility in handling 

 became more and more perfected. In the Fu generation the pro- 

 duction had dropped to 159 per pair despite the fact that the sterile 

 females had been practically eliminated. This led to an investi- 

 gation of the defect. It was found by isolating the eggs of the 

 females of the Fi4 generation, which had been placed with a num- 

 ber of their own males, that only 32 per cent hatched. And yet 

 in the same experiment under identical conditions 58 per cent of 

 . the eggs of the F^ female hatched when paired with the males 

 from the truncate stock. Moreover, the males of the F14 genera- 

 tion were able to fertilize 52 per cent of the eggs of the females of 

 the truncate stock. 



