DUNN 



the extreme of which is complete al- 

 binism, or entire absence of pigment, 

 leaving the fur clear white and the 

 eyes pink. The pinkness of the eye is 

 due to the absence of pigment in the 

 iris, which is typically colored by 

 black or brown pigment granules, so 

 that the blood in the capillaries on 

 the retina is directly visible. This 

 variation is to be sharply distinguished 

 from "partial albinism," a term which 

 has been applied, unwisely it now ap- 

 pears, to the occurrence of white 

 spotting in animals whose eyes retain 

 their full color. The color of the eyes 

 is an important point of distinction be- 

 tween complete albinos and spotted 

 animals. Cases of true albinism have 

 been reported in nearly ali he families 

 of rodents. Data from only h " of the 

 commonest families are given here, 

 the families being listed roughly in 

 the order of their relationship from the 

 more primitive to the more special- 

 ized.^ 



Leporid<£ — Oryctolagus cuniculus — 



European "rabbit." 

 Scmridce — *Marmota monax — 

 Woodchuck. 

 *Sciurus hudsonicus — 



Northern red squirrel.^ 

 *Sciurus carolinensis leu- 

 cotis — American gray 

 squirrel. 

 *Tamias striatus lysteri — 

 Chipmunk. 

 Muridce — Mus musculus — House 



mouse. 



^ I have followed the older order of clas- 

 sification which includes the Leporids in the 

 Rodentia. 



■* Through the kindness of Professor Bar- 

 rows of the Michigan Agricultural College 

 and Prof. W. E. Castle of Harvard Univer- 

 sity the writer has learned of the capture of a 

 pair of albino red squirrels by A. E. Secord, 

 of Wheeler, Michigan. Breeding experiments 

 to test the inheritance of this variation were 

 to have been attempted but expense and 

 pressure of other work have prevented the 

 writer from undertaking the project. 



Hystricidce- 

 Caviidce — 



97 



Ratrus norvegicus — ■ 



Common rat. 

 *Microtus pennsylvanicus 



— Meadow vole. 

 *Fiber zibethicus — 



Muskrat. 

 Peromyscus leucopus 

 noveboracensis — Deer 

 mouse. 

 *Erethizon dorsatum — 



Canada porcupine. 

 Cavia cobaya — Guinea- 

 Pig- 



The inheritance of the albinism has 

 been studied in the rabbit, the house 

 mouse, the house rat, the deer mouse 

 and the guinea-pig. In all of these it 

 is due to a gene which acts as a Men- 

 delian recessive to full color. At the 

 same (albino) locus in the germ plasm 

 have occurred other mutations. In the 

 rat, a change in this locus has produced 

 both albino and its dominant allelo- 

 morphs ruby-eyed dilute, in which 

 the reduction of the melanic pigments 

 is visible in the generally lighter tone 

 of black, coupled with a complete ab- 

 sence of yellow. In the guinea-pig 

 three graded variations have occurred: 

 ( 1 ) dilution, resulting in a reduction 

 of all pigments; (2) ruby, resulting in 

 the absence of yellow, and the further 

 reduction of black and brown in fur 

 and eyes to very light shades (prob- 

 ably homologous with the ruby varia- 

 tion in rats); and (3) Himalayan al- 

 binism, which determines the absence 

 of yellow and the restriction of black 

 and brown to the extremities, ears, 

 nose, feet, and rump, while the eyes 

 are pink. These three conditions are 

 distinct in appearance, do not blend 

 in crosses and are all alternative allelo- 

 morphs with full color and with each 

 other. No complete albinism is known 

 in the guinea-pig. In the rabbit two 

 changes have taken place: Himalayan 

 albinism (probably homologous with 



