SELECTION IN BAR-EYED RACE OF DROSOPHILA. 



are very nearly alike and there is no essential difference in the 

 ratio of males and females. This agrees with the results obtained 

 by MacDowell in his work on extra bristles. In the present 

 experiments sex-linkage might have been expected from the 

 fact that the ratio between male and female averages did not 

 remain constant from generation to generation. The factors 

 for converting the female means to the male standard in the 

 seven generations of upward selection are successively 1.91, 

 J -73' I -53. 140. 1-36, i 60, 1.57. Those for the downward selec- 

 tions are 1.57, I 86, 1.43, 1.79, 1.51, 146 and 1.40. But it is 

 impossible to relate the differences in the offspring to differences 

 in the parents. 



The appearance of full-eyed males and heterozygous females 

 in the stock and selected lines may be explained in two ways. 

 It may have been due to the carelessness of the author in pre- 

 paring the food, feeding and transferring the flies, or it may 

 have been due to reverse mutation in the race. 



The precautions taken by the author were not such as to 

 exclude absolutely the possibility of the entrance of an egg here 

 and there. But in spite of that fact the evidence is almost 

 irrefutably against the theory of contamination. Perhaps it is 

 well to state here in detail the author's methods. The pre- 

 cautions in regard to the preparation of food have already been 

 given. It is sufficient to add that no larvae ever appeared in the 

 food jar. In all of these experiments the food was handled by 

 means of an all-metal scalpel. This was used chiefly because 

 it could be easily cleaned and could be kept absolutely clean. 

 During the first two generations of VBa selections the author 

 depended upon the fact that Drosophila does not as a rule lay 

 eggs on a clean, dry, metal surface and merely kept the scalpel 

 clean but did not heat it before using. In all succeeding work 

 it was heated in an alcohol flame just before being used. All 

 vials and bottles that had been used were boiled and rinsed in 

 tap water and were then kept inverted on the table until they 

 were again used. In the VBa selections no filter paper was 

 used with the food. In the Ba selections the clean filter paper 

 was kept in a table drawer and was removed only at the time of 

 using. Fresh cotton for the plugs was also kept in table drawers. 



