DUNN 



all of these types the white-spotting 

 varies onlv^ within general limits. In 

 other piebald mice and in guinea-pigs 

 especially it appears purely at ran- 

 dom, in irregular blotches hardly ap- 

 proximating any pattern at all. The 

 spotting may also vary in amount from 

 a few white hairs to over half the sur- 

 face of the animal, although in general 

 the pigmented 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 list which has 

 been hastily compiled does not repre- 

 sent the true distribution of this varia- 

 tion among rodents in general. 



Leporidie — Oryctolagus cuniculus 

 Sciuridte — *Sciurus finlaysoni 

 Muridee — Mus musculus 



Rattus norvegicus 

 *Evotomys gapperi 

 Caviidie — Cavia cobaya 



In the rabbit, rat, mouse, and 

 guinea-pig the similarity of its inherit- 

 ance points toward a homology in 

 this variation. Data on its localization 

 are lacking except that in mice it is 

 probably not located in the same chro- 

 mosome with albinism and pink-eye, 

 nor with the black-eyed white-spot- 

 ting about to be discussed. In rats and 

 guinea-pigs it is likewise not linked as 

 far as is known with any other color 

 variation, while in rabbits it may be a 

 property of the same locus at which 

 English or dominant spotting is de- 

 termined. 



The two other categories of spot- 

 ting are peculiar each to a single spe- 

 cies. 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, likewise a dominant, is ap- 

 parently peculiar to mice although 

 wild rodents resembling this type have 



101 



been reported (e.g., Sciiinis finlay- 

 so?ii). 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 hy- 

 brid, always throwing, when bred 

 pure, a ratio of two black-eyed whites 

 to one piebald. The cause of this pecu- 

 liarity has lately been traced to its 

 association with another lethal factor 

 which determines the death in utero 

 of all pure black-eyed white zy- 

 gotes. 



BLACK 



One other color variation is com- 

 mon enough in rodents to make com- 

 parison profitable. This is the discon- 

 tinuous change from the "agouti" 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 development of black 

 and brown pigments. It is always pres- 

 ent in wild "agouti" 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 follow- 

 ing species: 



Leporidce — Oryctolagus cuniculus 

 *Lepus americanus 



virginianus — Eastern 

 varying hare 

 Sciuridce — *Sciurus hudsonicus 



*Sciurus niger ludovicianus 

 *Sciurus niger niger 

 *Sciurus carolinensis leucotis 

 *Tamias striatus lysteri 



