MUTATIONS IN EYE-COLOR OF DROSOPHILA. 343 



It is seen that all the results are consistent with the assumption that the 

 darker females are due to two doses of the C factor and the light females to one 

 dose of the same factor. The two kinds of females differ in this one respect 

 alone. The males having only one X have in consequence only one dose of the 

 C factor, and are light in color, no dark males being possible. 



In the red, vermilion, and pink-eyed flies no difference in shade between the 

 females and males has been made out with certainty, although in these, as in the 

 Eosin, the females have two doses of P, 0, and C, and the males only one do.^ 

 Correspondingly, in the heterozygous flies of red and pink (made by crossing 

 white males to females of these colors) no difference in shade was observed, 

 although the heterozygous females had only one dose of P, and C. But in 

 the orange stock, mixed with "its own" white, Mr. Bridges has been able to 

 distinguish two classes of females: very dark orange and light orange, which 

 proved on being tested to contain respectively two doses and one dose of and C. 

 But in this case, unlike that of the Eosin, the orange males are like the dark 

 (homozygous) females and not (as in the Eosin) like the light, orange female > 

 In consequence a light orange male is as impossible as a dark eosin male. The 

 following crosses will serve to illustrate the statements just made: 



Dark orange 9 190 

 Tk 1 , u t • ui r, Dark orange & 182 



Dark orange * by Light orange 9 j ^ onmge 9 lgl 



White orange <? 187 



Light orange 9 80 



T . , . w , . , Dark orange <? 62 



Light orange 9 by White orange * -j WWte onmge 9 26 



White orange cf 41 



Pink 9 117 



Light orange 9 by Pink & \ Dark orange cf 61 



White orange & 70 



Composition of the White Eye Mutants. 



It has been shown that the assumption that the eosin eye lacks the orange 

 factor, but contains V and P, is in conformity with the experimental tests. Its 

 white associate lacks both the orange and the C factor as shown by the same tests. 

 It has been possible to show that all white-eyed flies lack both and C, and not 

 simply C as formerly assumed. 1 This is made evident by crossing an eosin male 

 to a white female (of the red class). All the female offspring should have red 

 eyes if the ordinary white contained orange. But the female offspring from this 

 cross do not have red eyes but light-eosin eyes. This latter condition can only 



1 Both assumptions however give the same results in all cases except where eosin is involved, and the* 

 fore the earlier view was justified. 



