MENDEL'S LAW AND THE HEREDITY OF ALBINISM. 385 



made by Cuenot. By back-crossing hybrid grays with the ancestral white stock he 

 obtained gray as well as white individuals, which in the phraseology of breeders 

 should be \, f, f , etc., white "blood," yet all the grays, irrespective of ancestry, gave 

 precisely similar results in crosses with whites, viz., equal numbers of gray and white 

 offspring. 



It is evident, then, that when a pure gray race of mice is crossed with a pure 

 white race, the gray character invariably dominates in the offspring, and in subse- 

 quent generations both gray individuals and white individuals occur approximately 

 in the proportions demanded by Mendel's principles of dominance and segregation. 

 No better illustration of Mendel's law has yet been produced than is afforded by the 

 cross between gray and white mice. 



2. In Other Mammals, in Fishes, and in Plants. In the case of guinea-pigs, we have 

 many times mated together albinos born of mottled parents, or obtained by mating a 

 mottled with a white animal, but never with any but the expected Mendelian result, 

 all the young being albinos. 



In the case of rabbits, the same law appears to hold. Professor R. T. Jackson 

 kindly placed at our disposal last summer three white rabbits, a male and two females, 

 all born in the same litter, of spotted parentage. The two females have borne by 

 their brother, in three litters, seventeen young, all albinos. 



In man, Farrabee (:03) and Castle (:03) have recently shown albinism to be in 

 all probability recessive. 



As to fishes, Dr. Hugh M. Smith, of the United States Fish Commission, informs 

 us that in one of the State fish-hatcheries of this country there is bred as a curiosity 

 a race of albino trout which "breed true," indicating that the albino character is 

 recessive. 



In plants more than two-thirds of the Mendelian cases mentioned by de Vries 

 (:02, p. 146) are cases of " depigmentation " of flowers or fruit, the depigmented con- 

 dition being invariably recessive in crosses with the normal condition. 



It appears, then, that in organisms in general albinism behaves as a recessive 

 character in heredity.* 



* The only exception known to the writers is the dominance of white plumage, in certain crosses of poultry, 

 as recorded by Bateson and Saunders 002). Yet the dominant character in this case is one of partial albinism 

 only, and its dominance is not invariable. We suspect that the dominance of white plumage results from its 

 coupling in the gametes with some other character strongly dominant by nature. 



