134 PROCEEDINGS OF THE AMERICAN ACADEMY. 



pigment character, it follows that the albino gametes of a black animal 

 contain only that pigment character v^hich gives black. Consequently 

 if two black animals, each having albinism recessive, are crossed, the 

 albinos that result contain only that pigment character that makes for 

 black. The truth of this hypothesis may be readily tested by breeding 

 these albinos to pure black animals, the expected results being that only 

 black offspring will be produced. This expectation has been fully real- 

 ized in the experiments of the writer. Albino mice both of whose 

 parents were black, have, in numerous crosses, produced no other color 

 type than the black, when bred to black mice. This held true irrespec- 

 tive of the origin or degree of relationship of the black animals used. 

 Whether black- white mice were used, or those wholly black derived 

 from the house-mouse cross, or even a black stock purchased of a dealer, 

 the result was the same, so far as the production of black pigment was 

 concerned. This result is the same as that obtained by Cuenot ( : 03), 

 who had albinos from a cross of two black mice, and found that they 

 gave only blacks when bred to black animals. A similar case is recorded 

 in "Taf. 2," of von Guaita's (:00) later contribution. His pair 3, 

 consisting of an albino and a black animal, produced, in 11 litters, 16 

 black-white mice, 7 black, and 20 albinos. The parents of the albino 

 used in tliis cross were a black and a black-white mouse, so that their 

 albino young would possess the black pigment character only. 



Additional evidence that the writer's black mice and the albinos ob- 

 tained from them possessed only the two pigment characters that give 

 black (i. e., black and chocolate) is afforded by the cross of black with 

 chocolate animals. This cross, even supposing the pigment character of 

 the black animal in some cases to become resolved into black and choco- 

 late, would then afford but two combinations of pigments, namely, black 

 with chocolate giving black, or chocolate with chocolate giving chocolate. 

 If, however, the yellow character is present in a latent state in either 

 parent, the cross should bring it into activity and a proportion of gray 

 young should result. Thus far the writer has known of no case where 

 gray young did occur in a mating of this sort. Two crosses were 

 made in which a black-white female (403) was bred to two choco- 

 late-white males, and each of the two litters thus obtained consisted of 

 an albino and four black-white mice. That is, black was dominant over 

 the chocolate. Again, an albino, both of whose parents were black, and 

 which therefore should possess the black character, was bred to a choco- 

 late female, and of the four young produced, two were albinos and two 

 were black. Another albino mouse, also of black parentage, was bred 



