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JOURNAL OF MAMMALOGY 
hibiting this variation show a general quantitative reduction in the 
black and brown pigments in both fur and eyes. A certain amount 
of pigment is present in the iris but not enough to obscure the blood 
color of the retina. Yellow pigment is not affected. Pink-eyed animals 
with the ‘‘agouti^^ coat pattern therefore appear yellow since the black 
bases of the dorsal hairs are a reduced slaty or bluish tint and are covered 
by the fully intense yellow parts of the hair. Black animals with this 
variation are slaty or bluish all over in mice and a dirty near-white 
in rats and guinea-pigs. Its distinctness from albinism becomes evident 
when pink-eyed colored animals are crossed with albinos. The first 
generation offspring in this case are all as fully colored as the wild type 
and if inbred produce full colored, pink-eyed colored, and albino young. 
The variation occurs in the following species: 
Sciuridoe — *Marmota monax. 
Muridce — Mus musculus. 
Rattus norvegicus. 
*Microtus pennsylvanicus. 
*Fiber zibethicus. 
CaviidcE — Cavia cobaya. 
Its occurrence in the species marked * is probable but is based only on 
museum specimens with the coat colors peculiar to pink-eyed animals. 
The eyes in the mounted specimens may or may not agree with the 
original. 
Data on the localization of this variation are available in large num- 
bers for mice, and in lesser amount for rats and guinea-pigs. In these 
species it is a simple Mendelian recessive to full color (dark-eye). In 
rats and mice it is certainly a homologous variation, in appearance, 
in inheritance and in localization, for a large amount of hnkage data 
indicates that the genes for pink-eye and for albinism are located in 
the same chromosome and at about the same relative distance apart. 
This localizes both of these genes in both species, and leads to some in- 
teresting conclusions and speculations which will be more fully consid- 
ered later. In guinea-pigs there is incomplete evidence concerning 
the location of the gene for pink-eye but some data which Dr. Sewall 
Wright has kindly extracted from his breeding records and sent to me 
indicate that the locus of pink-eye is not in the albino chromosome but 
elsewhere. As we shall see, this may prove just as instructive con- 
cerning the homologies between species in germinal constitution as the 
more definite localization of the gene in rats and mice. 
