DISTRIBUTIVE COLOR FACTORS. 29 



"Pink-eyed" colored varieties are much "yellower" in appearance than 

 their corresponding dark-eyed intense and dilute forms. This is due to two 

 facts : 



(1) That in such forms as the pink-eyed black agouti and pink-eyed brown 

 agouti (both intense and dilute) the yellow band of the agouti pattern is left fully 

 pigmented, while the black and brown pigment in the same hairs is much reduced in 

 amount. Similarly pink-eyed yellow animals possess fully pigmented yellow 

 hair and thus have as heavily pigmented coats as do the dark-eyed yellow types. 



(2) In the pink-eyed black and pink-eyed brown varieties (intense and 

 dilute) there are no yellow pigment granules in the hair, but the extremely small 

 amount of black or brown pigment present gives the optical effect of an animal 

 with yellow pigment. This is especially marked in the case of the pink-eyed 

 brown variety. 



The mutual independence of the factors D and P, and of their modifica- 

 tions d and p, was recognized by Castle and the writer (1909) and found to hold 

 good in all the color varieties, whether possessing the agouti pattern or not. 

 At that time we reported the cross of a dilute "dark-eyed" animal with an 

 intense "pink-eyed" animal, resulting in the production of a "dark-eyed in- 

 tense " Fi. We had then only a small number of F 2 animals from such crosses, 

 but those showed that the four theoretical classes of offspring were produced. 

 In similar crosses we have now obtained the following result: 



Observed. . . 

 Expected. . . 



Dark-eyed Dark-eyed j Pink-eyed Pink-eyed 

 intense. dilute. intense. dilute. 



71 32 28 6 



77 25.7 2.5.7 8 6 



Other crosses showing the independence of D and P have been made, and 

 the results all follow the expectations with reasonable accuracy. Miss Durham 

 (1911) has also recognized the independence of D and P, but without giving 

 numerical results showing the occurrence of the intense and dilute types of the 

 various pink-eyed color varieties. She, however, recognizes the independence 

 of pink-eye and dilution only in those mice "in which yellow is absent." The 

 fact that their independence has been observed and experimentally proved in 

 animals (agouti) in which yellow is present seems to remove this restriction. 

 Thus, for example, the cross reported in 1909, and already referred to, shows 

 that their independence is clear-cut, even in the individual hair, and that the 

 presence of yellow in the hair aids in showing their independence; for in the 

 dilute agoutis (browm or black) all the pigment in the hair is reduced in amount, 

 while in the pink-eyed agoutis (brown or black), the yellow band in the hair is 

 as heavily pigmented as in dark-eyed agouti forms. 



We may now consider, in order, the two factors which have to do with the 

 relative distribution of the three pigments, yellow, brown, and black, in the 

 hair and skin. These factors A (agouti) and R (restriction), already briefly 

 described, have certain characteristics in" common, and evidence exists (as will 



