STRUCTURE OF APPENDAGES 315 



epidermis and in the fatty masses of and beneath the corium, and is 

 probably identical with the yellow color of fat in other portions of 

 the body and in the yolk of the egg. A yellow shank, in a heavily 

 laying hen, soon loses a part of its pigment; this is also noted of 

 the coloring matter in other parts of the body. This fact indicates 

 that the coloring matter of the fatty part of the egg yolk is from 

 the same source as that of the fat. The draught of this substance 

 is more than normally and the reserve is being drawn upon. Feed 

 rich in zanthophyll and carotin cause intense yellow colored yolks, 

 and feeds poor in these substances cause the yolks to be a pale 

 yellow. Cotton seed meal contains two pigments, one a yellow 

 crystalline substance and the other a brownish resinous substance. 

 Both of these pigments are probably deposited in the egg yolk. The 

 eggs of some hens contain a large quantity giving a light brownish- 

 yellow color to the yolk. 



The brown or black-brown pigment is carried in microscopic 

 pigment granules, which may be scattered through the ordinary 

 cells or may be confined to special pigment cells. The former are 

 confined to the epidermis; the latter may be found in both layers, 

 but infrequently in the epidermis. When granules are present in 

 the flattened cells of the corium, they occupy the nuclear region. 

 They lie in short thin lines while those of the under portion of the 

 Malpighian layer occur in oval groups. Where these granules occur 

 in the rete layer, they cluster around the nuclei. In the colored 

 skin there are dark pigment granules found in the corium and to a 

 less extent in the rete layer. Hanau has described a definite cellu- 

 lar body which he found densely packed among the black-brown 

 granules. There is a central body which sends out branches in all 

 directions. In very dark skinned shanks these ramifying strands 

 interlace, and form a compact network, which in many cases is so 

 thick as to give the impression of a homogeneous mass. Here and 

 there occur round or oval pigmented bodies, which Hanau concluded 

 were the star-shaped cells with their pseudopod-like appendages 

 contracted. Pigment cells commonly lie around blood-vessels, clearly 

 indicating their course. They frequently form a compact tube, but 

 more often are limited to fragments which only partly enclose the 

 vessels. Pigment cells occur in several well-defined localities: in the 

 upper portion of the cutis among the closely interwoven strands of 

 connective tissue; in the region bordering the blood-vessels; in prox- 

 imity to nerves, in nerve endings and in surrounding fat masses. 



