152 PROCEEDINGS OF THE AMERICAN ACADEMY. 



merit characters. A cross was made between a golden-agouti male and 

 an albino female of black parentage, which therefore had only the black 

 pigment character. This union brings together in the heterozygote all 

 three pigments, and consequently only gray offspring are expected. All 

 the eight young from this pair were, in fact, gray. The result is, there- 

 fore, quite similar to that obtained by mating black with golden-agouti 

 mice, for, as previously stated, gray young usually are produced. Black 

 individuals may result, however, from such a cross as this. Their 

 occurrence is due probably to the union of a gamete having the black 

 character (from the black parent) with one having the chocolate charac- 

 ter (from the golden-agouti parent). 



Finally, a golden-agouti was mated with an albino female of the 

 extraction indicated by the following diagram : 



(J bl.-wh. 1 • 2 b. 9 wh. S wh. 9 house mouse 



i gr. 82 gr. 81 S gr. 51 9 wh. 



S wh. 256 9 wh. 192 



9 wh. 335 S bl.-wh. 227 



9 wh. 448 



This albino, 448, when mated with a golden-agouti male, 484, pro- 

 duced 2 gray and 2 golden-agouti young. The ancestry of the black- 

 white grandparent, 227, is unknown, beyond the fact that it was of 

 a stock which had been crossed with chocolate as well as with black 

 individuals. In this mating, it is necessary to assume a segregation of 

 characters in such a way that one-half the gametes of the albino female, 

 448, contain no black element. Union of such gametes with the choco- 

 late-yellow gametes of the golden-agouti male would pi-oduce golden- 

 agouti young. The gray character may have come wholly through the 

 white female, 335, certainly its black constituent did, so that it seem.s 

 necessary to assume also that the black-white ^, 227, had chocolate 

 recessive. 



After many crosses, it was at last possible to obtain albinos both of 

 whose parents were golden-agoutis. The same mating produced also 



