No. 576] 



VARIATION IX DEOSOPHILA 



727 



flies, or more in the crosses with White-eyed flies than 

 in those with Black body color. (In every case, where 

 the contrary is not stated the flies are normal in other 

 respects than the one named, e. g., White-eyed flies in 

 these crosses have Gray bodies and Long normal wings.) 



No explanation of this specificity by the assumption 

 of a segregation of factors in the germ cells appears to 

 be available here, though such a possibility lias not yet 

 been ruled out, or can be ruled out till certain other phe- 

 nomena are understood. The easiest way of "explain- 

 ing" it is that the dominance of the genes for Beadedness 

 varies in accordance with many other circumstances, 

 among which are differences in the other genes present, 

 such as those for Vermilion, White or Pink. Such an 

 assumption as this, as will appear later, would seem to be 

 fully in accord with the behavior of the genes for Beaded 

 wings when in still different relationships. 



It is assumed, then, for example, that the percentages 

 of Beaded-winged flies in the Fj generation of a cross 

 between Beaded and White are higher than those in the 

 Fj generation of a cross between Beaded and Black, be- 

 cause the gene for Black is relatively to the gene for 

 White eyes an inhibitor of Beadedness. It would appear 

 as though a series might be made of the mutants of 



in which the Beaded genes are recessive. In order to 

 construct such a series a large number of pairs would 

 have to be made for each cross in order to determine the 

 limits of variability of Beadedness for the cross con- 

 cerned. The work would probably be greater than the 

 value of the results obtained, and therefore the attempt 

 has not been made to carry out this test. From what has 

 been done incidentally in carrying out other experiments, 

 it will be seen that in general the darker eye colors and 

 body colors are associated with a low percentage of 

 Beadedness in the Fj generation, and the brighter colors 



