MULTIPLE ALLELOMORPHS 165 



not occurred at the locus of the vermilion factor, 

 however, but at another locus where there had been a 

 normal factor. Subsequent work with the cherry 

 eye color showed that it was allelomorphic to white 

 and to eosin, the three eye colors and their normal 

 allelomorph forming a quadruple system. 



To the preceding history must be added cases of 

 the return mutation from eosin to white. Such a 

 mutation occurred in 1914 in a culture of eosin flies 

 with miniature wings. The parents had been treated 

 with alcohol, but there is no evidence to show that 

 the alcohol had any connection with the event. A 

 single white eyed male appeared among many 

 hundred eosin brothers and sisters. The male had 

 miniature wings. When crossed by ordinary white 

 it produced white through two generations. There 

 can be little doubt that it is the same white as 

 the original white. In a pure bred stock, eosin 

 tan vermilion, a few males were found which had 

 a white eye color instead of the cream color of 

 eosin vermilion. These flies mated to white stock 

 gave white offspring for two generations. Here the 

 case was checked by two control characters, for 

 the new white-eyed males showed tan body color 

 and were proved to carry vermilion. In these 

 controlled cases the mutation took place in the 

 reverse direction from the original one. Three 

 other cases of eosin returning to white which are 

 apparently not explainable by contamination are also 

 recorded. 



The appearance of eosin in the white-eyed stock 



