62 p. W. WHITING AND HELEN DEAN KING 



In fully colored ticked guinea-pigs the hairs of the back are 

 sepia at the base and black toward the tip except that a narrow 

 yellow band occurs on almost every hair at the short distance 

 from the tip. In blacks the hairs are similar except that the 

 band is lacking. Thus the intense guinea-pig is darker than the 

 intense rat, for the hairs of the latter are white at the base. As 

 described by Wright, there is in the guinea-pig a gradual decrease 

 in the amount of yellow pigment from the intense, CC, through 

 the various dilute combinations, CdCd, dCr, CdCa, until the red- 

 eyed dilute, CrCr, shows no yellow at all. In this animal the 

 hairs are dark sepia banded near their tips with white. The 

 dilute carrying albinism, CdCa, has light sepia hairs banded with 

 light cream. Wright explains the correlation of the lighter sepia 

 with the presence of yellow by assuming that in the animal 

 CdCa there is competition in the oxidation of chromogen between 

 the compound black producer, enzyme I-II, and the yellow pro- 

 ducer, enzyme I. In the animal CrCr the yellow producer has 

 been removed and enzyme I-II is free to act on chromogen with- 

 out competition. All of these grades of pigmentation in the 

 guinea-pig are darker than the ruby-eyed dilute rats, as is also the 

 most dilute combination obtained in the guinea-pig, the red-eyed 

 carrying albinism, CrCa. In this animal the hairs are light sepia 

 to the base and are ticked with white near the tip. 



The ruby-eyed dilute gray rat, A. CrCr, has no yellow pig- 

 ment, but the yellowish tinge, as seen in the white rat, is notice- 

 able in the lighter parts of the hairs; the black pigment is re- 

 duced to a very light sepia and is confined to the tips of the 

 hairs. In the ruby-eyed light sepias, a. CrCr, the pigment is 

 likewise very dilute, but extends from the tips well down the 

 hairs. The base, however, is without pigment, as in the black 

 rat. Thus the agouti and non-agouti dilutes can be distinguished, 

 not by the presence or absence of bands, as in the guinea-pig, 

 but by the greater extent of the pigment in the non-agoutis. 

 The coat-color of the fawns, CrCa, is extremely dilute, midway 

 between that of the homozygous ruby-eyes and that of the 

 Albinos. 



The hairs of agouti red-eyed yellow rats, A.rr, are yellow and 



