THE AMERICAN NATURALIST [Vol. XLVIII 



ag would have been formed and this would have given 

 only agoutis and albinos in a 3 :1 ratio, while Hagedoorn 

 reports "73 agouti, 37 blacks 1 and 32 albinos." 



The case then is nothing so simple as "repulsion" or 

 "coupling," it includes failure to segregate and com- 

 plete disappearance of a dominant Mendelian factor; G 

 the factor for agouti. 



Since numerous investigators of color inheritance in 

 mice have never found the agouti factor anything but a 

 normal Mendelizing factor epistatic to black, and since 

 Hagedoorn himself seems to have become mixed in his in- 

 terpretation, it seems that the case proves or shows little 

 until a satisfactory answer can be found to the question 

 of what has become of the agouti factor. 



Conclusions 



The facts above given lead to the following conclu- 

 sions : 



1. The so-called dominant type of spotting in mice does 

 not differ from "self" color by the presence of a unit 

 character which 1 1 self ' ' lacks. The presence and absence 

 hypothesis fails to account for the shifting dominance 

 seen in spotting in mice. 



2. It is misleading to describe, under the same symbol, 

 the so-called "dominant" spotting of mice and the Eng- 

 lish spotting in rabbits. 



3. It seems probable that differences in "dominance" 

 of spotting in mice are due to modifying supplementary 

 factors and such spotting might be termed "unsup- 

 pressed" and "suppressed" spotting rather than "domi- 

 nant" and "recessive" in the Mendelian sense. 



4. Hagedoorn 's hypothesis of repulsion between the 

 color factor, A, and the agouti factor, G, is incorrect. 



November 19, 1913. 

 i Italics mine. 



