SHANK COLORS IN DOMESTIC FOWL. 243 



size, these cells, when situated in the epidermis occupy a space 

 similar to that filled by several of the Malphigian cells. 



Immediately below the epidermis in all specimens examined 

 a space was found a little less in width than that of a row of 

 columnar cells which was practically devoid of pigment. It was 

 impossible to find a single instance in which the pigment cells 

 of the corium penetrated those of the epidermis, although 

 Kerber (15) observed them in the chick embryo. 



Zoomelanin is the name given to black-brown pigment in 

 birds by Bogdanow (i) according to Gadow (2). 



THE PIGMENT RELATIONS IN THE VARIOUS SHANK COLORS 



OBSERVED. 



White. — Here both lipochrome and melanin pigments are 

 wanting. Gadow (2) observed regarding the coloring of feath- 

 ers : "'VoUkommene Brechung aller eintretenden Lichtstrahlen, 

 ohne Pigment, verursacht weiss," which would apply equally 

 well to the skin though, of course, in the skin one never finds 

 the ivory white of feathers except in the ear-lobes in certain 

 breeds. Melanin pigment may be present in the corium of 

 white shanked birds, either at considerable depths or in quan- 

 tities insufiicient to make itself noticeable. In old birds of 

 yellow shanked breeds, particularly those which have been 

 heavy layers, the yellow of the epidermis frequently disappears 

 and white consequently results. The white shank in this case 

 has a different appearance, however, from that in hereditarily 

 white shanked birds. The thickness of the scales in pure white 

 shanked birds has little to do with the color. 



Yellow. — This color results from the presence of zooxanthin 

 in both layers of the epidermis, or in the corneum alone. It is 

 diffused through all parts of the cells and intercellular sub- 

 stances. In brightly colored shanks both epidermal layers ex- 

 hibit a rich supply of this oil. In young birds the amount in the 

 Malphigian layer is large ; as the chick grows this gradually dis- 

 appears. Old laying hens carry a very small quantity in the 

 horny layer; the rete appearing white to the naked eye. Old 

 hens which for some cause, pathological or other, have never 

 laid possess a deep orange color in both parts of the epidermis. 

 The intensity of the coloration in such cases would seem to indi- 

 cate that the original supply of hpochrome pigment had not 



