132 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



Possibly this difference in results is flue to a difference in the nature 

 of the albinos used, and in the readiness with which the pigment elements 

 undergo resolution. If, as is apparently the case, all the black animals 

 in the writer's experiments contained both black and chocolate pigments, 

 it follows that when the black or the yellow pigment elements became 

 segregated from the other two in gamete formation, they must regularly 

 have been eliminated, so that the individual resulting from two gametes 

 of a similar pigment nature was either golden-agouti or black (i. e., black- 

 chocolate). Similarly if the black and the yellow elements remain 

 coupled, they are regularly eliminated, leaving only the chocolate ele- 

 ment in the gamete, for no black-yellow type of mouse is certainly 



known. The chocolate element on the 

 other hand may occur either alone or in 

 combination with black or with yellow, 

 giving in the one case, on union with a 

 similar gamete, a chocolate individual", and 

 in the other, either a black (i. e., black- 

 chocolate) or a golden-agouti. 



The researches of Cuenot ( : 03), as well 

 as those of other experimenters along 

 similar lines, show clearly that in crosses 

 between albino and pigmented individuals, 

 the former, although showing no pigment 

 Solid line indicates colors or com- colors, have nevertheless an equal share 

 binations of colors whicii may in the transmission of pigment characters, 

 result by segregation. Whatever may be the nature of the pig- 



Dotted line indicates colors or , ■, ■ i „ 4. -t • 1 ■ *v t 



, . , ment-producmg elements, it is plain that 

 combinations of colors wliicii * ° 



the albino possesses these, and that they 



undergo segregation as in pigmented ani- 

 mals. The occurrence of the black het- 

 erozygotes, iu the cross of black-white with 

 albino mice, was certainly due to the union of gametes each containing 

 the black-chocolate characters alone. For black mice regularly produce 

 gametes with these pigment characters only, and it is therefore evident 

 that the albino parent produced a certain number of gametes bearing the 

 black-chocolate pigment character (or none). These uniting with those 

 produced by the black-white mouse, resulted therefore in black animals 

 having albinism recessive. Yet with the albino character went also the 

 ability to transmit black-chocolate, but no other colors. 



In a few cases albinos were crossed with black mice derived from the 



riGCKE 7. 



did not result by segregation in 

 the writer's experiments, though 

 theoretically possible. 



