388 MENDEL'S LAW AND THE HEREDITY OF ALBINISM. 



individual. Strong evidence in support of this view is afforded by the experiments 

 of Haacke, von Guaita, and Darbishire, as well as by our own experiments, in crossing 

 spotted with albino mice. We bred to albino females two spotted males of a black- 

 white stock whose individuals bred true inter se. The offspring were like those obtained 

 by Haacke in crossing Japanese dancing mice with albinos, namely, mice uniformly 

 gray or black in color, though sometimes with a fleck of white on the belly, or with 

 one or more white bands on the tail. Of the forty-three young produced by this 

 cross, twenty-eight were gray and fifteen black. The fact that no albino offspring 

 were produced shows that the spotted males formed no recessive gametes, but only 

 those which were either mosaic or else purely dominant in character. But if domi- 

 nant gametes had been formed by segregation from a dominant-recessive mosaic, 

 we should expect that by a residual process recessive gametes would be formed also. 

 The latter not having been formed, it is safe to suppose that the former were not 

 formed either, but that all the gametes formed by these spotted males were mosaic. 



That the albino character entered as a latent constituent into the gray or black 

 hybrids formed by the cross just described is shown conclusively by the character 

 of their offspring. When bred inter se they produced albino as well as pigmented 

 offspring, and approximately in the ratio, 1:3; or, when bred to albinos, in the 

 ratio 1:1. 



Accordingly, in the original cross described, we have a case of simple dominance 

 of the pigment-forming over the albino character. This dominance is attended, 

 in about two cases out of three, by reversion to the particular form of pigmentation 

 found in the wild house-mouse. The reversion is due to the coming into activity 

 of a capacity (previously latent) to form yellow pigment, which with black pigment 

 forms gray. This latent capacity must have been present in one or the other or 

 possibly in both of the parents crossed. 



Darbishire's results differ from ours only in degree, not in kind. He, too, gets 

 invariably dominance of the pigment-forming over the albino character, and this 

 is associated in all except sixteen out of one hundred and fifty-four cases with rever- 

 sion to the ancestral kind of pigmentation, gray. The chief differences between 

 his results and our own are as follows: 



1 . In our experiments yellow was the latent constituent of gray which was brought 

 into activity by a cross with albinos; in the experiments of Darbishire black was 

 the latent constituent brought into activity. 



2. In our experiments white disappeared for the most part from the bodies of 

 the hybrids; but in Darbishire's experiments the disappearance of white was much 

 less complete. There was a strong tendency for the mosaic gamete to dominate as 



