COLOR. 61 



pendently by different factors, the combination of which gives doubly 

 dilute colors, which may still be classed in the same series. Dilute 

 guinea-pigs of this series have been called blue in the literature, but 

 the name is as inappropriate as it would be applied to human brown 

 hair, and, moreover, tends to confusion with the very distinct type 

 of dilution of the blue rabbit. In this paper the colors of this series 

 will be called sepia. Grades of dilution have been represented by 

 numbers, as in the yellow series. White is considered as grade 16. 

 Grading has been done by comparison with standard samples of hair, 

 the colors of which are defined in terms of Ridgway's colors at the 

 end of this section. 



(3) The most intense grade of this series is a rich dark brown, such 

 as is found in chocolate guinea-pigs, mice, and rabbits and in liver- 

 colored dogs. This color is not very different from sepia 4 , but is some- 

 what warmer and less dull. As noted by Miss Durham in the case of 

 brown mice, there seems to be a complete absence of black granules, 

 but a large quantity of brown granules. No intergrades between this 

 brown and black are known. There are dilute browns, each corre- 

 sponding closely to a color in the sepia series. They are often difficult 

 to distinguish from grades of sepia in isolated samples of hair. On the 

 animals, however, the browns seem conspicuously richer than the 

 sepias. There are, further, correlated differences in skin and eye color 

 which are even more conspicuous. 



Most guinea-pig colors can be matched fairly well in the sepia, 

 brown, or yellow series, but one other class of variations must be noted. 

 The animals have been graded by the color near the tip of the hair, but 

 while in some blacks, sepias, browns, and yellows the hair is nearly 

 uniform, in most cases the base is much duller than the tip. This gives 

 a somewhat streaky effect to the fur. In the case of dull blacks of this 

 kind, the color at the base of the fur is usually between a neutral slaty 

 black and a dark sepia. 



SKIN COLORS. 



The color of the skin usually corresponds roughly to the color of the 

 hair which comes from it. Where the fur is thick there is very little 

 pigment in the skin, while exposed places (as ears and feet) are often 

 very strongly pigmented. 



Where the fur is yellow the skin in exposed places shows an orange- 

 yellow color, usually with considerable admixture of black. On most 

 of the body the skin is white, with occasional orange-yellow spots. 

 The dilution of fur color is accompanied by dilution of the skin color. 



Where the fur is black the exposed parts of the skin are very black, 

 while the rest of the skin is dull black. Where the fur is of the sepia 

 series the color of the ears and feet depends much on the genetic factors 

 responsible for the dilution of the black. In the sepias of the albino 



