12G PROCEEDINGS OF THE AMERICAN ACADEMY. 



obtained, 3 were black. This fact points to a segregation of the color 

 characters both in the gametes having the albino character and in those 

 having the pigment character. In crosses with heterozygotes from tliis 

 house-mouse-albino stock no colors other than gray and black were 

 obtained. 



Of the black mice obtained from this stock by the process of back- 

 crossing already described, some proved to have albinism recessive, while 

 others were pure in respect to albinism, showing that the black condition 

 was not one depending for its production on the union of a recessive with 

 a dominant gamete, though the former (recessive gamete) was probably 

 effective in transmitting pigment. The black mice were found to pro- 

 duce only black pigmented mice and albinos ; their case is more fully 

 discussed under the next heading. 



Gray heterozygotes obtained by crossing house mice with albinos were 

 bi'ed to animals similarly colored but descended from black-whites and 

 albinos. All of their pigmented young, 19 in number, were likewise 



The reversionary gray coat of mice derived from a cross between 

 black-white and albino mice is not always transmitted intact, but com- 

 monly undergoes more or less resolution of its pigment characters. 



Thus, three pairs of gray-white mice, whose grandparents on the side 

 of each parent were respectively a black-white and an albino, and whose 

 parents were gray heterozygotes, produced gray young in large propor- 

 tion, but also a few golden-agouti and a few black individuals. The total 

 offspring from three such pairs was 1 4 gray- white, 1 black-white, 4 golden- 

 agouti-white, and 1 albino. This seems plainly to be a case of resolution 

 of the gray pigment character, as there was no golden-agouti ancestor, 

 so far as known. 



Gray house mice, when bred to fancy stocks of other colors, usually 

 give gray young only. Thus, only gray mice were obtained by the 

 writer from a cross of a female house mouse with a black-white male. 

 These gray young were then bred to gray heterozygotes derived from a 

 cross of a house mouse with an albino, and only gray offspring resulted. 

 Dehne ('55) records crossing a yellow mouse with a house mouse, hoping 

 thereby to propagate the yellow variety, but all the young were gray, 

 and the experiment was given up. Cuenot (: 03) fiiuls that the cross of 

 wild gray mice with black mice always results in gray otlspring in the 

 first generation, but in the second generation the black character reappears 

 under close breeding, in the proportions demanded by the Mendeliau 

 laws for recessive characters, i. e., 3 gray to 1 black. 



