RUBY-EYED DILUTE GRAY RAT 61 



linked with each other, are Hnked with albinism. If this be the 

 case we should expect to find them linked with ruby-eyed dilu- 

 tion. The failure of the double recessive, ruby-red, to appear 

 in the F2 generation is further corroboration of the linkage of the 

 two loci. 



The ruby-eyed dilutes have an eye-color distinctly lighter 

 than that of the red-eyed yellows. The ruby-white compound, 

 CrCa, which we have called fawn from the coat . color, has an 

 eye-color still lighter. A comparison of eye-colors in the rat 

 has shown a gradation from black to pink as follows: black, 

 PP. RR. CC; red, PP. rr. CC; ruby, PP. RR. CrCr] light ruby, 

 PP. RR. CrCa.; pink, pp. RR. CC; light pink, PP. RR. CaCa. 

 Other combinations may show intermediate grades. 



The coat-color of the ruby-eyed dilutes is a very light sepia 

 showing more or less yellowish white. The yellow tinge is 

 probably due to excretions from the skin, since there are appar- 

 ently no yellow granules. Albinos and hooded rats also show 

 this yellow tinge in the hair, especially as they grow older. 



Wright ('15) has shown quadruple allelomorphs in the albino 

 series of guinea-pigs. He has further discussed the matter 

 ('17 a) in a general scheme of color inheritance for mammals. A 

 comparison of conditions in the rat with conditions in the guinea- 

 pig will be of interest. 



In the wild Norway rat the hairs are white at the base. Very 

 gradually black pigment granules appear toward the tip and in 

 all of the larger hairs these increase without interruption until 

 the hair becomes intense black. In the hairs of intermediate and 

 small size, however, the black pigment usually gives place to 

 yellow granules which extend almost the entire length. The ex- 

 treme tip is black. Some of the smaller hairs have black pig- 

 ment in a single uninterrupted row of granules and others are 

 white. A few of the smaller yellow-banded hairs have the band 

 rather narrow and close to the tip. In almost all cases, however, 

 when the yellow band occurs, it is very wide. In the black rat 

 most of the hairs are white at the base, becoming black or dark 

 sepia toward the tip, while a few of the smaller hairs are white 

 throughout their entire length. 



