96 Experimental Zoology 
AYVAY, and CYAY. In other words, selective fertilization 
occurs. 
It seems to me that this is improbable and that a simpler 
assumption may account for the results. Cuénot’s yellow mice 
were obtained through an albino of unknown ancestry. He 
crossed them with gray (or with black) mice, and obtained 
dominant yellow mice, to which he assigns the formula CYCG. 
These when inbred should give, according to Cuénot, on the 
theory of disjunction of the gametes, CY- and CG-gametes. 
The offspring would then give the Mendelian proportion— 
1 CYCY +2 CYCG+1 CGCG. 
But no mice represented by CYCY were obtained. It seems 
to me more probable from the results that the yellow does not 
separate from the other colors, and if so all the germ-cells 
would be on my view CY(CG) or (CY)CG. Such forms 
inbred would not give CYCY, as Cuénot assumes, but the 
dominant heterozygote CY (CG). 
This point of view assumes that the yellow is so slightly 
prepotent in the extracted dominant, CY(CG), that the gray 
may dominate in half the germ-cells, giving CY(CG) and 
CG(CY). If this is true, gray mice would appear in one-fourth 
of the offspring of these dominants. The yellows differ on 
this point of view from all other extracted dominants in the 
failure of the yellow to remain dominant in the germ-cells.- 
Schuster has made a number of pairings between gray and 
white mice. Seventy of such families (Fy) were gray;* two 
families contained yellow mice and gray mice; one family con- 
tained four chinchilla mice only; and one contained two chin- 
chillas and one gray. The appearance of these yellows in the 
first hybrids is ascribed by the author to the presence of yellow 
in the white parents,—the yellow dominating the gray of the 
first hybrids. Whether the same explanation will account for the 
chinchillas is not known, because the dominance of the chin- 
chilla has not been tested. 
} Containing 342 mice. 
