604 PROCEEDINGS OF THE AMERICAN ACADEMY. 



no albino offspring are produced. But the disappearance of albinism in 

 this case is not final. The albino character has not ceased to exist, but 

 has merely become latent in the offspring. It will reappear unimpaired 

 in the next generation if the cross-bred individuals be mated inter se. 



II. Complete Albinism a Recessive Character. 



The disappearance of the albino character for a generation, and its 

 subsequent reappearance under close breeding, show that it is inherited 

 in conformity with Mendel's law of heredity,* and that it is, in the 

 terminology of that law, a recessive character. 



(a) In Mice. 



In mice this has been conclusively demonstrated by Cuenot (:02),t 

 who, on crossing wild gray house-mice with albinos, obtained always 

 gray mice indistinguishable in appearance from the pigmented parent. 

 Yet these gray hybrids, when bred inter se, produced both gray and 

 white offspring approximately in the Mendelian ratio, 3:1. The exact 

 numbers recorded are 198 gray: 72 white, or 26.6 per cent albinos. 

 According to Mendelian principles the grays of this second filial gener- 

 ation should consist in part of pure grays, which would not transmit the 

 albino character, and in part of hybrid grays like their parents, — the 

 first filial generation, — which would transmit alike the pigmented and 

 the albino characters. This Cuenot demonstrated to be actually so, 

 for certain pairs formed by random selection of the grays gave only 

 gray offspring (189 individuals) ; the remaiuiug pairs produced albino 

 as well as gray offspring, and in the expected ratio, 3 grays : 1 albino. 



* A brief statement of Mendel's law has been made by one of us elsewhere 

 (Castle, : 03 a ). For a fuller exposition, see Bateson (: 02), Bateson and Saunders 

 (:02),de Vries (:02), or Correns (:01). 



t In an earlier paper (Castle, : 03 a ) the first published recognition of the reces- 

 sive nature of albinism in mice is erroneously credited to Bateson (:02). The 

 papers of Cuenot (:02, :02 a ), which at that time were unknown to us, apparently 

 antedate Bateson's. 



Crampe ('85) seems to have been the first to recognize clearly that the first 

 cross between pigmented and unpigmented (albino) varieties gives rise, in the case 

 of rats, to pigmented individuals, not to albinos. Crampe crossed gray, black, 

 gray-white, and black rats (Mus norvegicus) with albinos, and found that in each 

 cross the albino character disappeared. He noticed also that the albino character 

 might reappear in subsequent generations, but he did not discover the conditions 

 necessary for this reappearance beyond establishing that albino offspring were 

 produced under close breeding by those pigmented rats only in whose immediate 

 ancestry there had been a cross with the albino form. 



