244 MAINE AGRICULTURAL EXPERIMENT STATION. I914. 



been used up and also that an additional supply had been ae 

 posited. As this fat is present in the scales it is but natural that 

 the intensity of their color should be influenced by their thick- 

 ness. Consequently when the pigmentation is weak as in old 

 laying hens the scales on the anterior portions of the leg possess 

 the brightest shades. However, in non-laying birds the portion 

 covered by the small lateral scales often appears darker. In 

 this instance the less deeply pigmented thick anterior scales have 

 the effect of diluting the color as a whole. In yellow legged 

 young chicks the pigment is distributed evenly around the shank. 

 since the richly colored Malphigian cells are more influential in 

 determining the resultant color than the incompletely formed 

 and still growing scales. 



Blue. — In blue shanked birds zoomelanin is present only in 

 the corium. The blue color is the optical effect resulting when 

 this dark pigment is seen through the semi-translucent Mal- 

 phigian stratum. As Krukenberg (7) has noted, "Das Blau 

 ist alto hier eine sog. optische Farbe, eine Erscheinung, welche 

 liberall da zu Stande kommt, wo das Licht ein triibes Medium 

 durchdringt und von einer schwarzen Unterlage aus alsdann 

 reflectirt wird." As no pigment granules lie in the horny layer 

 the thickness of the scales is scarcely concerned in affecting the 

 depths of color, save where yellow fat occurs. In most of the 

 blue-shanked birds examined the number of pigment cells in 

 the corium was greater than in black legged individuals, and 

 they generally fromed a more compact network, however in- 

 sufficient observations were made to make this conclusion gen- 

 eral. The depth of blue color depends directly upon the number 

 of these cells. 



Black. — Black shank color results when melanin pigment lies 

 in the epidermis and only under these circumstances, so far as I 

 have observed. It may be heightened by pigment cells in the 

 upper cutis, but pigment in the outer layer is essential to pro- 

 duce the black color. As has been noted two forms of black 

 pigment occur in the epidermis; granules in both layers and 

 pigment cells in the rete. The granules resemble in size the 

 nuclear elements brought out when the tissues are subjected to 

 nuclear stains. In the more deeply colored birds the epidermis 

 is deeply peppered with these particles, the Malphigian layer 

 contains numerous melanin pigment cells, and underneath in 



