562 THE AMERICAN NATURALIST [Vol. XLYIII 



front of the muzzle is white. The white chevron on the 

 muzzle of several antelope (Strepsiceros, Taurotragus) 

 is probably the result of a similar restriction of ear 

 patches combined with a centrifugal nose patch, leaving 

 a white line between. The black dorsal stripe seen in 

 many mammals and the black tail tip are probably mani- 

 festations of centrifugal pigmentation. The latter mark 

 is common in stoats {Mustela) and among those that 

 change to a white coat in winter, as the ermine, the tail 

 tip still remains black. In sundry other genera, as 

 Genetta, a black tail tip is part of the normal pattern. 



In their paper on albinistic negroes, Simpson and 

 Castle (1913) published some highly interesting photo- 

 graphs of "piebald" individuals. In four persons of one 

 negro family the hair over the median part of the head 

 from the occiput to forehead is pure white, as though due 

 to a restriction of the aural pigment patches. In addi- 

 tion, more or less of the median area of th,e back, as well 

 as the hands (including much of the forearms) and feet 

 (including the lower part of the ankle) are pigmented. 

 These latter areas may represent centrifugal pigmenta- 

 tion, but it should be noted that this is present in the 

 dermis. Possibly there is a close relation between dermal 

 pigment and that produced in the centrifugal style of 

 pigmentation. 



Among birds, the black of the outer tail feathers of the 

 ptarmigan (Lagopus) may be comparable. A black area 

 is also sometimes present on the middle of the throat, or 

 as in certain gulls the outer primaries may be black. 



This form of pigmentation is not found universally and 

 the conditions governing its appearance are unknown, 

 though its heredity in the "Himalayan" rabbit has been 

 somewhat studied by Professor Castle. 



Summary 



The principal points of this paper may be summed up 

 as follows: 



1. In mammals and birds that normally are com- 



