212 MULTIPLE ALLELOMORPHS 
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 
