SELECTION IN BAR-EYED RACE OF DROSOPHILA. 37! 



results of Castle correspond more nearly to the facts observed. 



The results obtained from these selections can best be made 

 out by consulting Table I. and Figs. I, 2 and 3. 



The attempt to select downward was entirely unsuccessful. 

 The selection was never very rigid, but the average of the off- 

 spring persistently remained above that of the stock. 



The upward selections were more successful. In hi5 the males 

 rose from the stock average of 96 to 147 and the females from 

 54 to 101. In the other two lines where smaller numbers of 

 offspring were obtained the rise was not quite so large. The 

 second and third generations, however, failed to give any further 

 increase in the facet number. Upward selections taken from 

 line 15 after the first generation failed to give any rise in the 

 facet number. The line x3 was taken from li after two genera- 

 tions of downward selection and gave a decrease in the facet 

 number in spite of the fact that the male had 222 facets and 

 was mated to average females. 



The line 16 was intended to be a downward selection from hi5, 

 but the parents proved to be very near the mean and all matings 

 from the first generation were sterile except f 1-6. This particular 

 mating involved a male with 34 facets, the lowest number ob- 

 tained in these experiments. Fortunately a fair number of 

 offspring was obtained. The males average much lower than 

 those of the previous generation and about the same as those of 

 the low lines hatching at the same time, but the females average 

 much lower than anything obtained elsewhere. It is likely that 

 the male with 34 facets was a mutant and that the mutation 

 chiefly concerned the sex chromosome. The complete sterility 

 of this race prevented any further investigation. 



The results here obtained are very different from those re- 

 ported by Zeleny and Mattoon. In their selections all three 

 generations went gradually upward and gradually downward; 

 in these experiments there was a sudden rise in the upward 

 selected lines in the first generation and no further effect, and 

 no response at all in the downward selected lines. For that 

 reason and also on account of the high degree of sterility it seemed 

 best to make some selections in the long-winged stock used by 

 Zeleny and Mattoon. 



