^ HEREDITY OF BODY COLOR IN DROSOPHILA 43 



One can not work with these body colors without being im- 

 pressed by the similarities between the brown and the black 

 flies on the one hand, and the yellow and the gray on the other. 

 Brown and black lack the yellow factor, and if this, as I suppose, 

 acts to some extent as an inhibitor the resemblance is manifest; 

 while conversely the presence of the yellow factor in the yellow 

 and in the normal fly makes clear their resemblance. One 

 is tempted to surmise that black and brown may both be stages 

 of the same chemical reaction, which surmise would be more 

 probable if it could be shown that both factors are contained 

 in the X chromosome, but this relation in itself could not be 

 used as an argument to urge their dependent chemical nature. 



