DISTRIBUTIVE COLOR FACTORS. 



33 



yellows, black-eyed dilute yellows, and brown-eyed dilute yellows in the "dark- 

 eyed" series; (2) pink-eyed yellows and pink-eyed dilute yellows in the pale 

 series. The experimenter can not distinguish by external appearances the black 

 eyed and broAvn-eyed forms of the pink-eyed yellow series, and so must class 

 them together unless breeding tests be applied. 



The "yellow" coat of mice is due to as true a pattern factor as is the agouti 

 coat, and the investigator errs when he considers the "yellow coat" a lower 

 stage of development of a black or brown coat. Yellow pigment appears in the 

 ticked or agouti coat by the action of a factor whose function is of a restrictive 

 or inhibitive nature. In a very similar fashion yellow pigment appears on a 

 greater scale in the coat of the "yellow" mouse. 



"Yellow" in mice is no more allelomorphic to gray than is gray allelomor- 

 phic to black. Castle, as already stated, has shown that the factor which pro- 

 duces the ticked or gray coat is allelomorphic to its absence, not to black or any 

 other pigment. It is an excellent thing to simplify gametic formulse when this 

 can be done with the support of experimental evidence, but the experimental 

 work should precede the "simplification" unless a false impression is to be 

 produced. 



If yellow animals are crossed with non-yellow, equality of yellow and non- 

 yellow young is approximated. The following numbers have been obtained : 



Several litters of young have been produced b}^ yellows nnxted inter se since 

 the publication in 1919 of figures showing approximately a 2 to 1 ratio. The 

 additional observations are: 



If these figures be added to those obtained by Miss Durham (1911), by 

 Cuenot (1903), and by Castle and the writer (1910), the following result is 

 obtained: 



