CHARACTERS IN HEREDITY 167 



brown and cinnamon-gray rabbits produced by 

 the same mutation, loss of factor B, which has 

 produced brown and cinnamon-agouti varieties 

 among mice and guinea-pigs. Again there must 

 be in all rodents a factor Y which, acting in the 

 presence of C, produces yellow pigment, but Y 

 has not unmistakably revealed itself by getting 

 lost. It is always present, if C is, and may rep- 

 resent possibly a step on the road to the produc- 

 tion of black and brown. Certainly, however, 

 its distribution on the body of the rabbit is inde- 

 pendent of the factor E, though subject to U. 

 In the diagram, therefore, Y and Br will prob- 

 ably fall into the positions shown herewith for 

 the guinea-pig: — 



U B 



I / \ 

 A— C^Y E 



I \ / 

 I Br 



This diagram would express the interrelations 

 of the color factors, as we now understand the 

 matter, in a reproductive cell or gamete trans- 

 mitting the wild type of coat. But such a 

 gamete might be formed by some sixty-four dif- 

 ferent kinds of wild-coated individuals. The 

 only differences, however, between these sixty- 

 four kinds of individuals would lie in whether 

 they contained a single or a double dose of each 

 of the factors enumerated. I therefore propose 



