UNIT-CHARACTERS OF RODENTS 



123 



because of its defective vision. For the eyesight of the albino 

 is very poor owing to the imperfect pigmentation of its eyes. 

 Albino sports accordingly never become very common in a 

 wild species but are probably among the earliest formed 

 domestic or tame varieties, because of their striking character 



Table 12 

 Some Unit-Characters of Rodents 



and the ease with which a distinct variety is established. 

 For, being recessive, the albino variation is secure as a racial 

 character as soon as a pair of albinos has been isolated.^ 



The albino variation is commonly considered to be the re- 

 sult of a recessive variation in a color factor whose dominant 

 phase is expressed by the symbol, C, its recessive or albino 

 phase by c. (See Table 12.) 



Another color sport occasionally observed among wild ro- 

 dents, and which is the basis of distinct varieties among 



^ The contemporary origin of an albino race of field mouse (Peromyscus) has 

 recently been recorded (Castle, 1912) in a species in which neither this nor any other 

 of the common color sports had previously been recorded. 



