No. 583] BOLE OF ENVIRONMENT IN DROSOPHILA 411 



In III 90 one GRN <$ (the only one present) when tested 

 gave GRAb and $ and GWAb <$ and ?. 



In III 113 GEN" ? to GWN <$ gave GWAb and ? and 

 GRAb ?. 



These results show without any question that in the 

 great majority of cases the phenotypic normal class (when 

 abnormality is expected) is in reality made up largely 

 (entirely, except for cross-overs according to expecta- 

 tion) of genotypically abnormal individuals. Their ab- 

 normality is shown by suitable breeding tests such as 

 those here recorded. 



INFLUENCE OF THE FACTOR FOR BLACK OX TJIK REALIZATION 

 OF THE ABNORMAL CONDITION 



Some of the evidence seemed at times to indicate that 

 flies heterozygous in black are less likely to show the ab- 

 normal abdomen, but even if this is true it is still uncer- 

 tain whether this might not be due to other conditions 

 than those caused directly by the heterozygosity for black. 

 It might be that the black stock contained other factors 

 that influence the cross. Moreover since the number of 

 eggs laid by a given kind of female determines how many 

 larva* will appear in a given time, and since the relation 

 of the larvae to the food is an important factor in the 

 results, it seemed hazardous to put any emphasis on such 

 results. 



In order that the heterozygous flies might be reared 

 under conditions that the control showed were favorable 

 for development of the abnormal condition in homozy- 

 gous forms, some black, red-eyed normal females were 

 mated to gray, white-eyed abnormal males. After the fe- 

 males were fertilized they were put into a new bottle with 

 some of the stock white-eyed females (fertilized). Some 

 of the daughters were red- and some white-eyed; all of 

 the latter were very abnormal, but the red-eyed females 

 (heterozygous) were all normal through five counts. At 

 the fifth count the white-eyed males that had been ab- 

 normal up to this time became normal. The result is in 

 accord with many similar observations ; for as conditions 



