30 THE INHERITANCE OF COLOR IN MICE. 



be discussed later) that they may be closely related. Their sphere of action is 

 limited to the hair and skin, to the exclusion of the eye. In this respect they 

 differ fundamentally from the distributive factors D and P, already described. 



6. The Distributive Factor, A. 



This factor was first recognized by Cuenot (1902) under the designation of 

 G (firm), as producing the pattern seen on the coat of the wild house-mouse ; but 

 he erred in considering the factor G as allelomorphic to the factor N {tioir) for 

 the production of black pigment. Castle (1907o) proved that in guinea-pigs 

 the agouti pattern is a unit character allelomorphic to its absence. Guided 

 by this hypothesis he formed a new color variety of guinea-pig (cinnamon). 

 Furthermore, he proved (1907a) that the agouti pattern might be carried by 

 certain red animals, which when crossed with blacks produced agouti young in 

 the first generation. By experimental test it was proved that all black animals 

 behaved the same in the crosses made and that the reds differed. Morgan 

 (1911a) quotes Castle as stating that in the above-mentioned crosses both the 

 blacks and reds were able to transmit the agouti type of coat. Having thus 

 misquoted Castle, Morgan offers as a suggestion the explanation which Castle 

 proved was correct in 1907. 



The agouti pattern consists in mice (Allen, 1904) of two chief types of dor- 

 sal hairs: (1) Those having a fine block tip, a sub-apical band of light ochraceous 

 color (occupying about one-fifth of the hair) and a dark plumbeous basal por- 

 tion. (2) Others, less numerous, are black throughout. 



The ventral hairs Allen describes as possessing a distal half, which is dirty 

 white to pale ochraceous buff, and a basal half which is plumbeous. Castle 

 (19076), in describing the agouti pattern in guinea-pigs, states that the tips are 

 black in hairs showing the ticking; then follows a yellow or red band, and then 

 the hair is black to the base. Both of these investigators find that the ' ' ticked ' ' 

 hairs have black tips, as does Hurst (1905) in the case of rabbits. 



Morgan (1911a) states that he has obtained black animals which have cer- 

 tain of their hairs brown-tipped. These he characterizes as agoutis without the 

 yellow band and further states that the ticked hairs in the coat of ''agouti" 

 animals are brown-tipped. It is obvious that he is dealing with a color pattern 

 in his "gray" (agouti) animals which is not identical ivith the agouti pattern as 

 described by other investigators. It tends, therefore, to confusion to treat the 

 pattern that he is dealing with as agouti. Furthermore, it seems probable 

 that the blacks, which he reports as having ticked {brown-tipped) hairs, do not 

 possess a factor in the least comparable with the "agouti" pattern. Morgan 

 himself states that these brown-tipped hairs occur oyily in heterozygous black 

 mice. The question suggests itself, how can mice possess, as a result or neces- 

 sary concomitant of heterozygosis, a pattern which is the characteristic of a 

 homozygous wild race? 



Bateson (1903) stated that in black mice the tips of the large contour hairs 

 are often brown. Ticked hairs in non-agouti (black) mice are not, then, a new 

 development, and as black mice have been long used in experiments and have 



