124 PROCEEDINGS OF THE AMERICAN ACADEMY. 



A partial albino may be regarded as a mosaic exhibiting, in its soma, 

 two characters which, when segregated, are to each other as dominant 

 (pigment) to recessive (albinism). Two partial albinos breed true to 

 that (partial albino) condition, even though each contains an albino char- 

 acter recessive (compare formula 2a, p. 73). Necessarily, therefore, two- 

 thirds of the spotted offspring of such heterozygous animals (DR'R) 

 come of the union of a gamete containing the character partial albinism 

 (DR) with one bearing the completely albino character (R). Yet the 

 union of a spotted animal with an albino not of spotted parents produces 

 young which tend to be totally pigmented. An albino coming of tioo 

 spotted parents, ou the other hand, when bred to a spotted individual, prob- 

 ably produces only s/^o^/eof offspring, for this union is manifestly similar to 

 that producing spotted young, where both spotted parents have albinism 

 recessive. 



Complete pigmentation in mice tends to be dominant over partial 

 pigmentation, although the dominance is not always perfect. In rats, 

 Crampe seems to have found the tendency to be toward an intermediate 

 condition. In general, the result of a union of a pure spotted and a pure 

 unspotted (pigmented) individual is to greatly reduce the amount of al- 

 binism in the young of the Fi generation or to eliminate albinism alto- 

 gether, the outcome being, in one case, an intermediate condition, in the 

 other, dominance of the character total pigmentation. 



Partial albinism, then, tends to be inherited as a distinct character and 

 in accordance with the Mendelian principles ; in mice it behaves as a 

 recessive in relation to total pigmentation. 



VI. Heredity of Pigment Characters. 



1. Tlie gray coat. The "wild gray" or typical house-mouse coat 

 has been shown by Miss F. M. Durham (Bateson, : 03'') to owe its color 

 to the presence in the hairs of three pigments, black, chocolate, and yel- 

 low ; these may be present in slightly different proportions, thus produc- 

 ing a lighter or a darker gray, or one with more than the usual amount 

 of yellow (sable). For the purposes of this paper, however, "gray" is 

 understood to mean that sort of coat in which all three pigments are 

 present, no particular regard being paid to the slight variations of lighter 

 or darker tint. This gray coat under cross-breeding may undergo reso- 

 lution, giving several distinct color types characterized by an absence of 

 one or two of the three pigments. In the writer's experiments the types 

 thus obtained were: (1) black mice, whose pigments were black and 

 chocolate, (2) golden agoutis, containing only the chocolate and the yellow 



