136 
JOURNAL OF MAMMALOGY 
it is likewise not linked as far as is known with any other color varia- 
tion, while in rabbits it may be a property of the same locus at which 
English or dominant spotting is determined. 
The two other categories of spotting are pecuhar each to a single 
species. The English broken spotting of domesticated rabbits is a 
Mendelian dominant to self-color and has no probable homologue in 
other species, while the black-eyed white-spotting of mice, hkewise 
a dominant, is apparently peculiar to mice although wild rodents re- 
sembling this type have been reported (e.g., Sciurus finlaysoni). This 
last variety is interesting in that it is less pigmented than any other 
type of spotting studied, some black-eyed white-spotted mice having 
pigment only in the eyes, while the rest of the pelt is pure white. It 
is discontinuous with piebald spotting, and is, like yellow, an unfixable 
hybrid, always throwing, wEen bred pure, a ratio of two black-eyed 
whites to one piebald. The cause of this pecuHarity has lately been 
traced to its association with another lethal factor which determines 
the death in utero of all pure black-eyed white zygotes. 
BLACK 
One other color variation is common enough in rodents to make 
comparison profitable. This is the discontinuous change from the 
^Egouti’’ coat to one which is black all over and it is probably due in all 
the species in which it occurs to a gene determining the exclusive de- 
velopment of black and brown pigments. It is always present in wild 
‘Egouti’’ type rodents and its appearance alone is conditioned by the 
change producing non-agouti,’ or the absence of the ‘‘agouti’^ pattern. 
Its recessive allelomorph is brown, which has occurred in rabbits, 
mice, guinea-pigs and possibly in rats.’ This gene is probably not 
linked with any of the other known genes in mice, but its relationships 
in other species have not been studied. The variation from agouti 
to black occurs in the following species: 
LeporidcB — Oryctolagus cuniculus. 
*Lepus americanus virginianus — Eastern varying hare. 
Sciuridce — *Sciurus hudsonicus? 
*Sciurus niger ludovicianus. 
*Sciurus niger niger. 
*Sciurus carolinensis leucotis. 
*Tamias striatus lysteri. 
Muridce — Mus musculus. 
Rattus norvegicus. 
*Fiber zibethicus. 
Caviidce — Cavia cobaya. 
