130 PROCEEDINGS OF THE AMERICAN ACADEMY. 



mice, so that the agreement between theoretical and observed is reason- 

 ably close. The albino offspring were not all tested, hence it is not 

 possible to say whether there were any among them which contained the 

 black character only, as this hypothesis would demand. On the whole, it 

 seems reasonable to believe that segregation did take place among the 

 albinos used, in the manner indicated. 



That albinos differ in their ability to transmit pigment characters has 

 been shown by Darbishire (: 02) and Cucnot(:03). The latter had 

 three sorts of albinos : (1) from gray ancestors, (2) from black parents, 

 (3) from two "yellow" mice of a complex ancestry. The same black 

 male bred to the first sort, produced always gray mice ; bred to the 

 second sort, always black mice; bred to the third sort, gray, black, or 

 yellow mice. To explain this result Cuenot has formulated the ingenious 

 and attractive theory that pigments are produced by the action of specific 

 ferments on a chroraogenic substance, and that an albino may transmit 

 the former but not the latter. He supposes that the albino of gray 

 parentage transmits the ferments corresponding to the different sorts of 

 pigments which constitute the gray coat, and so the union of such an 

 albino with a pigmented animal produces gray offspring. In like manner 

 the albino of black parentage transmits only the ferments which make for 

 black. Assuming that there is some such process as Cuenot has indicated, 

 it is easy to conceive of segregration taking place in such a way that 

 certain of the gametes of an albino provide one sort of ferment and other 

 gametes another sort. Thus, if the albinos used by the writer should in 

 half of the cases produce gametes with the ferments that give the gray 

 coat, while the other half had the ferments either for black-and-chocolate 

 or for yellow and chocolate, such a result as was obtained is readily 

 explainable. At present, however, such an hypothesis does not admit of 

 positive proof, although it seems clear that the albino of mixed ancestry 

 does in some way contribute the third pigment element to produce gray 

 offspring. 



The gray heterozygotes resulting from this cross of black-whites and 

 albinos of mixed ancestry, when interbred, show a further resolution of 

 the pigment characters. Those used by the writer were practically of a 

 uniform gray all over, with only an occasional trace of albinism, so that it 

 is evident that the albino parents transmitted the character total pigmen- 

 tation. Therefore, in generation Fo about ^ of the animals are spotted. 

 The colors obtained from the gray heterozygotes are : gray (32), gray- 

 white (11), black (8), black-white (1), chocolate (1), and golden-agouti 

 (2), as well as albinos (21). 



