Inheritance of Small Variations 209 



found, giving a color which lies nearer the red, between the 

 red and eosin ; this new color was called cherry. So we have 

 four grades or conditions of this single unit character. 



And now, with the minute attention paid to the distinction 

 of these grades of eye color, new grades began to come fast. 

 In the number of Genetics for November, 1916, Hyde adds 

 two new grades, one called "blood," near the extreme red end 

 of the series, the other called "tinged," near the extreme 

 white end; in fact, from the descriptions it requires careful 

 examination to distinguish these two from red and white, re- 

 spectively. Thus we have now six grades of this unit. And in 

 the same number of the same journal, Safir (1916) adds an- 

 other intermediate grade, lying between "tinged" and eosin ; 

 this he calls "buff." All these seven grades are diverse con- 

 ditions of the single unit factor, having its locus in a certain 

 definite spot in the X-chromosome. Such diverse conditions 

 of a single factor are known as multiple allelomorphs. 



So, up to date we know from the mutationists' own stud- 

 ies of Drosophila that a single unit factor presents seven 

 gradations of color between white and red, each gradation 

 heritable in the usual Mendelian manner. These grades are 

 the following: (1) red; (2) blood; (3) cherry; (4) eosin; 

 (5) buff; (6) tinged; (7) white. 



It would not require a bold prophet to predict that as the 

 years pass we shall come to know more of these gradations, 

 till all detectible differences of shade have been distinguished, 

 and each shown to be inherited as a Mendelian unit. Con- 

 sidering that the work on Drosophila has been going on only 

 about seven or eight years, this is remarkable progress 

 toward a demonstration that a single unit factor can pre- 

 sent as many grades as can be distinguished, that the grades 

 may give a pragmatically continuous series. 



Besides showing that a unit factor may thus exist in 

 numerous minutely differing grades, this case shows that a 



