Wilson — Agouti-hlack Colour in Rabbits. 591 



he contained both x and y ; and, since he threw agoutis and yellows from 

 ordinary Fl black, he also contained Y. So far, therefore, his constitution 



was y""^ 



As to the remainder, there are two alternatives — (1) That, in X'b usual 

 place, lie carried another factor, say X', which had the effect of making him 

 black in spite of the presence of Y; and (2) that, in addition to X and its 

 recessive, he carried this new factor X' and its recessive. In the former case 



X'v . ^•^' 



his constitution was ^' ; in the latter Xa;. The first of these hypotheses 



^ ^ Yy 



involves the assumption that x can have more than one alternative, the latter 

 that the rabbits to which the new factor was introduced were already carrying 

 its recessive x! homozygously. 



Consider meantime the first of these hypotheses, viz., that the constitution 



X' X 

 of No. 28 was y ,,' He was the progeny of a black Himalayan dam and 



a heterozygous yellow sire. An agouti was produced at the same mating.' 



XX X X 

 The constitutions of such parents are ordinarily and y ,,' '^^® ^^"^ 



factor X' must have come to No. 28 from his dam, because, had his sire 

 carried it, he could not have been yellow, and since the dam produced an 



agouti at the same mating, she must also have carried X, and her constitution 



X' Y 

 so far as the present question is concerned was therefore ^ 



We have now to find whether our hypothetical constitution for No. 28, 

 viz., „ * is in accordance with experimental results ; and, in doing so, we 

 shall discover the constitution of agouti-black. No. 28 was mated with two 

 different constitutions, viz., (tortoise) and ^ {F\ black). With the 



former he should have produced four different constitutions ; with the 

 latter eight. With the former the progeny should have split into two 

 groups as regards the Xqb, and these again each into two more as regards the 

 Y& ; while with the latter the progeny should have split into four groups as 

 regards the Xes, and these again each into two more as regards the Ys. Let 

 us write down the two sets of constitutions so produced with their correspond- 



X' X 

 ing colours. We shall find two constitutions not met with so far, viz., y 



and ^, and we have no difficulty in inferring that the latter is that of a 

 black rabbit, for, since X' can make No. 28, which contains Y, black, much 



' Journal of Genetics, vol. ii, p. 225. 



4s2 



