306 F. B. SUMNER AND H. H. COLLINS 



to green is 3.30 for the adult pelages, 3.25 for the juvenile. Thus 

 the quality of the yellow pigment appears to be closely alike in 

 the early and later pelages of the pallid mutant. Likewise, there 

 are no very wide differences in this respect between the pallids, 

 yellows and normal gambeli. 



TRUE ALBINOS 



True albinism has appeared but once in our cultures, although 

 many thousand mice have been reared since the commencement 

 of these studies-^*^ Two broods from a single pair belonging to 

 the first cage-bred generaton of P. m. gambeli (La JoUa race) 

 consisted of two albinos and six of the wild type. There was one 

 albino of each sex, both being fertile. At least one of the normal 

 color proved to be heterozygous; the others were either sterile 

 or their condition was not ascertained. 



These albinos have, as was to be expected, behaved as simple 

 mendelian recessives. A few matings between individuals 

 known to be heterozygous (other than the parents of this strain) 

 have given 7 normal and 6 albino young, an obvious excess of 

 the latter. Matings between albinos and heterozygotes, on 

 the other hand, gave 17 normal and 18 albino, which is as close 

 an approach as possible to the 'expected'-number. 



The mice of this strain (fig. G) are plainly complete albinos, 

 comparable with ordinary white mice, which are albinic house- 

 mice (Mus musculus). Indeed, the white Peromyscus are very 

 similar to the latter in appearance, differing chiefly in having 

 larger and more protruding eyes and somewhat longer ears. 

 They likewise differ in being almost completely odorless, as 

 are also normally colored specimens of Peromyscus. ^^ As al- 

 ready stated, the eyes of the albinos average much paler than 

 those of the pallids, the former being pink, the latter commonly 

 dark red. In both of these varieties, they are distinctl}^ smaller 

 (or at least protrude less) than in normal individuals. 



i^We have had as many as 1500 mice at one time in our 'murarium,' most of 

 these being cage-born. Tlie experiments have lasted seven years. 



^^ A single cage of ordinary white mice will impart a pronounced 'mousy' 

 scent to an entire room even when well ventilated. This is not true of a thousand 

 specimens of Peromyscus. 



