Wilson — Agouti-black Colour in Rahhiis. 593 



If these combinatious were all bred and identified, a number of crucial 

 experiments could be made. If tlie two groups homozygous for two 

 factors were mated with pure agouti, the progeny would all be agouti-black ; 

 and if the five groups heterozygous for one pair were mated with pure 

 agouti or pure ordinary black — with agouti when the group contained y ij, 

 and with black when it contained Y Y or Y y — half the progeny would be 

 agouti-black, while the other half would be black in one case and agouti in 

 four. But Professor Puanett's experiments were necessarily confined to 

 such groups as appeared early among the descendants of No. 28's dam, 



namely, to the two groups heterozygous for two pairs of factors, i.e. y n 



(No. 28) and y C''^® ^^'^^ agouti-blacks). The experiments with the 

 second group were the more satisfactory ; and we shall consider them 

 first. 



y "1 , agouti-black, was mated with three different kinds : (1) with itself, 



(2) with heterozygous yellow, and (3) with tortoise. Mated with itself, the 

 progeny should split into three groups so far as the Xes are concerned, viz., 

 X'X', X'X, and XX, and the middle group should be as numerous as the 

 other two together. Each of these should split again in a similar manner as 

 regards the Zs. Thus there should be nine groups in all, which we shall 

 set down in tabular form so as to show their constitutions, the expected 

 colours, and the relative number of individuals expected in each. 



Thus there ought to be 7 blacks : 6 agouti-blacks : 3 agoutis. The 

 expectation is in accordance with the experimental results.' 



Mated with heterozygous yellow, j^ the progeny of y « should split 



' Journal of Geuetics, vol. ii, p. 231. 



