ALLEN. 



THE HEREDITY OF COAT COLOR IX MICE. 



113 



mouse, the genal and nuclial centres are close together, and the two 

 patches are generally not distinctly marked off from each other. From 

 a comparative study of other mammals, however, it is found that the 

 genal patch is rather definitely limited in its backward extension to the 

 posterior part of the head proper, so that it is not dilHcult to assign it 

 limits in cases where the two are fused. On the subject of the arrange- 

 ment and variation of these patches in piebald mainmals, Professor Castle 

 and the writer have in preparation an extended paper based on the ex- 

 amination of a large number of animals. 



In a mammal such as the mouse, which normally has total pigmenta- 

 tion, partial albinism seems to occur but seldom in the wild state, and 



Figure 5. 



Figure 6. 



when depigmentation does take place, it is most apt to occur in a small 

 spot on the forehead, at the tip of the tail, or on the mid-ventral line. It 

 is as if the pigment patches emanating from the two nuchal centres, or 

 the two pleural centres, had not quite met, leaving a spot unpigmented 

 on forehead or belly respectively, or as if the sacral patches had not 

 spread to the end of the tail. There is great variation in the degree of 

 isolation of the various pigment patches delimited by the white areas. 

 Figure 4 shows the pattern of a mouse reared by the writer in which 

 appear the beginnings of separation (1) of the genal patches (giv- 

 ing rise to the white streak in the forehead), and (2) of the nuchal and 

 scapular patches (the small white spot in the median line at the nape 

 indicating the boundary of the two). The fore feet are white, showing 

 that the scapular patch has not reached its greatest possible extension. 



VOL. XL. — 8 



