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THE AMERICAN NATURALIST [Vol. LII 



way to scattered collections of these granules (which are 

 dark brown when seen singly) and later disappearing 

 altogether. In the transitional region, black and yellow 

 pigment may frequently be found in the same segment. 

 In most hairs, the dark bodies again replace the yellow 

 ones as we pass toward the tip; occasionally the yellow 

 continues as far as any axial region is distinguishable. 



The yellow pigment seems to be restricted to the axial 

 part of the hair. To some extent, it occurs in the form 

 of granules, but, unlike the black, it is largely present in 

 a diffuse condition. This pigment is not all of the same 

 tint, but varies in shade from a pale yellow to an orange 

 or even a very pale brown. 



For a varying length, on the distal, tapering ends of 

 nearly all the hairs of the colored parts of the body, there 

 is a very dark, granular pigment, lying close beneath the 

 surface of the hair. This overlies and reinforces the ax- 

 ial pigment, so that the distal end is frequently darker 

 than any other part of the hair. The superficial pigment, 

 where dense, commonly looks almost black, but when seen 

 in a thin layer the single granules appear brown. As 

 already stated, this is likewise true, though in lesser 

 degree, of the "black" axial pigment. In one of the 

 " mutants," to be described later, this distal dark zone is 

 nearly or quite lacking, and the same is true of certain ex- 

 ceptional samples of hair taken from normal individuals. 



The yellow pigment is readily soluble in even fairly 

 dilute potassium hydrate solutions, whereas the dark pig- 

 ment is very much more resistant to this reagent, and 

 may remain unchanged, even after the complete disinte- 

 gration of the hair. 5 



Most students of this subject seem to follow Miss Bur- 

 ham (Bateson, 1903) in recognizing three pigments in the 

 hair of Mas musculus — the black, the brown or chocolate, 

 and the yellow. After considerable examination of the 



