DILUTION EFFECTS IN CERTAIN EYE COLORS 465 



are more fundamental. ]\'Iiss Durham speaks for instance, of a 

 factor in mice that dilutes black to blue and chocolate to silver 

 fawn, and in cats Doncaster speaks of a diluter that changes 

 black to blue and orange to cream. We feel that too much of a 

 distinction has been made between so-called 'diluters' and other 

 factors which cause changes in color. We mean here by dilution 

 any effect that gives a Ughter color, and the factors that produce 

 such effects we speak of as diluters. The factors pink, vermilion, 

 eosin, and white we put in the general class, diluters, because 

 the colors produced by them are lighter than that of the wild 

 red fly. However, other eye color factors, that we know of, give 

 colors darker than the wild red, and these we speak of as 'inten- 

 sifiers.' Likewise in body color, yellow is lighter than wild 

 gray, and black is darker. This statement applies to the pure 

 recessive forms, pp (pink) yy (yellow) etc., and the lighten- 

 ing in heterozygous forms (whenever the effect shows) is essen- 

 tially the same. In the former case the two diluters (pp) act 

 as it were against the whole cell, in the latter, one diluter acts 

 against the same cell as well as against its normal allelomorph. 

 In the double recessive, such as vermilion pink, there are two pairs 

 of diluters acting together against the rest of the cell and the 

 dilution effect is roughly a summation of the effects of each. 



Whether pink, vermilion, eosin, and white eye colors are due to 

 losses from the original germ-plasm (presence and absence the- 

 ory) or whether each is due to the presence of another active 

 factor sustituted for the original allelomorph, cannot be answered 

 from the data here presented. The occurrence of multiple alle- 

 lomorphism in the red-white-eosin case suggests however that 

 the latter view is correct, and from other grounds (e.g., reversible 

 mutations) we have adopted it as our working hypothesis. In 

 connection with sex-linked factors there is perhaps a question of 

 real absence from the point of view that the female has two sex 

 chromosomes and two sets of sex-hnked factors, while the male 

 has only one sex chromosome and therefore only one set of sex- 

 linked factors. For instance, the vermilion male differs from the 

 vermilion female in that his single sex chromosome carries only 



