134 



SIMPLE HISTOLOGICAL ELEMENTS. 



Fig. 72. Fig. 73. 



Pigment-cells of the skin of the lamprey. (Qtieckett.) 



boa (Python tigris), white pigment-cells 

 are found. (Queckett.) The red spots on 

 the skin of the plaice are produced by 

 minute, irregular cells. Pigment-cells 

 are often found in the peritoneum of 

 fishes and reptiles; and the pigment se- 

 creted in its ink-bag, so called, by the 

 cuttle-fish, is used by artists under the 

 'sepia." 



Pigment-cells in tail of the tadpole. 

 The transparent ones are the young 

 cells, in which the pigment granules 

 have not yet appeared. 



Color of the Hair and Eyes. 



In connection with the color of the skin, that of the hair and 

 eyes should be alluded to; though the coloring matter may be 

 otherwise than black in case of either, and therefore is not always 

 melanine. 



The pigment coloring the hair is found generally both in the 

 cortical and in the medullary portions of the shaft ; and since hair 

 is an epithelial appendage, as will be shown, we might expect that 

 its color will correspond, within certain limits, with that of the skin. 

 Spots of black hair are found (as in the hog) to grow on patches of 

 skin of the same color. In the albino, on the other hand, the hair 

 is colorless. For the particulars, however, consult the section on 

 "The Hair." 



The color of the eye is determined by that of the iris, as is ex- 

 plained in the last chapter of this work. It is blue, hazel, and, in 

 some cases, nearly jet black. The conformity of color with that of 

 the skin (or the complexion) is not so rigid as is that of the hair; 

 and yet the disparity ranges within certain limits. The irides of 

 albinoes are of a pink color; since, not being covered with pigment- 

 cells, the numerous very minute bloodvessels of the iris are visible. 



