138 PROCEEDINGS OF THE AMERICAN ACADEMY. 



yellow with black mice obtained sables ( i. e. gray with brighter flauks ), 

 dingy fawns (i. e. predominately yellow associated with dark pigment), 

 and also some fully black individuals, but the yellow mice used by Miss 

 Durham were presumably not golden-agoutis. 



In the case of the gray and the black young obtained by the writer, it 

 may have been that the former represented those animals in which a 

 coml>ination of all three pigment characters had taken place. The case 

 of the few black animals, however, requires a different explanation. If 

 they represent a combination of black-chocolate and of yellow-chocolate 

 characters, then the yellow must have become latent. If, however, in 

 the case of the yellow-chocolate character chocolate has been segregated 

 in certain instances, then in those instances equal numbers of black and 

 of gray mice should result. This is expressed by the following scheme: 



bl.-ch. + bl.-ch. = gametes of black parent, 

 yell.-ch. 4- ch. = " " golden-agouti, 

 2 gr. + 2 bl. = Fi. 



If this segregation takes place in half of the gametes produced by the 

 golden-agouti, the total result is 3 gray to 1 black mouse, which is a rela- 

 tion not greatly different from that obtained, viz. : 7 gray, 2 black. But 

 if we assume this segregation on the part of the golden-agouti, it seems 

 reasonable that it should take place among the gametes of the black mice 

 too, giving thus a certain number of chocolate individuals. Yet none 

 occurred. Miss Durham's result also failed to show such a resolution 

 on the part of the black character. 



It is much more probable that the golden -agouti here employed may 

 have contained the chocolate character recessive, or, at any rate, that the 

 segregation resulted in gametes some of which had the yellow-chocolate, 

 and others the chocolate character. The result would be the same in 

 either case. 



Unfortunately the writer was unable to obtain a second generation 

 from the black offspring produced by the cross between a black and a 

 golden-agouti. A few of the gray young were tested, however, with the 

 following results. In one case, two of the gray young were bred together. 

 If the gametes formed were of two sorts, corresponding to those pro- 

 duced by the black and the golden-agouti parents respectively, the 

 following combinations would be possible : 



bl. -f gold.-ag. r:= gametes of gray ^, 



bl. -f gold.-ag. :=. •' 9, 



1 bl. + 2 gray -f 1 gold.-ag. = offspring. 



