No. 599] 



THE GENETIC BEHAVIOR OF MICE 



The brown-and-tan and brown- sable varieties are new. 

 They resemble black-and-tan and black-sables, respect- 

 ively, in which all black pigment in the fur has been re- 

 placed by brown pigment. The parallelism between the 

 two series is strongest at top and bottom ; red has no exact 

 counterpart in the black series, since its yellow is more 

 intense than that of sable. All members of the two series 

 when crossed inter se fluctuate about their parental mean 

 grade. The greatest fluctuations are noted among the 

 offspring of sables ; the least among black-and-tans and 

 reds. We suspect also that a like gradation occurs in the 

 amount and intensity of black and brown pigments in the 

 black and the brown recessives of these series, though on 

 account of the self color of these varieties this point is 

 difficult of verification, except by breeding tests. From 

 some tests which have been made and others which are 

 under way, the evidence seems to show that blacks from 

 sables and yellows have less intense young when crossed 

 with agoutis, than do the blacks out of pure black-and-tan. 

 Tables and curves for this cross will be given at a later 

 time. 



It is significant now that sables and black-and-tans may 

 be synthesized by a cross of blacks out of the black-and- 

 tan race with reds, showing that the black recessives carry 

 the same differentiating element as do the black-and-tans. 

 Such a cross produced 45 young, 20 of which were black- 

 and-tan or sable, while 25 were black. The F x blacks were 

 heterozygous for brown, inter se matings producing 3Z 

 blacks and 13 browns. 



When a black which was heterozygous for brown was 

 mated to a red, yellows falling in both the black and the 

 brown series were produced as follows : 



