DUNN^ — UNIT CHARACTER VARIATION IN RODENTS 
135 
of the pigments in the pelage. When pigmentation is present all over 
the pelt the condition is known as self or not-spotted. Spotting is inherit- 
ed independently of albinism, since certain albinos crossed with spotted 
animals throw only seifs, while other albinos derived from white-spotted 
colored stocks have given spotted offspring. An albino may therefore 
be genetically either self or spotted although unable to give evidence 
of this condition except in its offspring by a colored animal which sup- 
phes the gene for the development of color. 
On the grounds of its inheritance white-spotting in rodents may be 
classified in three categories. The first of these is piebald or Dutch 
spotting, apparently due to a gene recessive to self coloration and proba- 
bly independent of other coat color unit characters. It may thence 
be present with albinism, yellow, pink-eye, agouti or black (see below). 
Piebald animals may be characterized by a typical locahzation of the 
spotting in a belt or collar as in belted mice or Dutch rabbits; the 
spotting may be confined to the face (‘‘white-face’’ mice), or it may be 
distributed in a fairly uniform dorsal pattern as in hooded rats.^ On 
all of these types the white-spotting varies only within general limits. 
In other piebald mice and in guinea pigs especially it appears purely 
at random, in irregular blotches hardly approximating any pattern at 
all. The spotting may also vary in amount from a few white hairs 
to over half the surface of the animal, although in general the pig- 
mented areas exceed the white portions in total size. The belly is like- 
wise more susceptible to spotting than the dorsum. This variation has 
been noted many times in wild species and I am certain the present 
hst which has been hastily compiled does not represent the true dis- 
tribution of this variation among rodents in general. 
LeporidoB — Oryctolagus cuniculus. 
Sciuridce — *Sciurus finlaysoni. 
MuridoB — Mus musculus. 
Rattus norvegicus. 
*Evotomys gapperi. 
Caviidce — Cavia cobaya. 
In the rabbit, rat, mouse, and guinea-pig the similarity of its inheri- 
tance points toward a homology in this variation. Data on its locali- 
zation are lacking except that in mice it is probably not located in the 
same chromosome with albinism and pink-eye, nor with the black- 
eyed white-spotting about to be discussed. In rats and guinea-pigs 
A hooded Microtus has been noticed in the Museum of Comparative Zoology 
at Harvard University. 
