590 Scientific Proceedings, Royal Dublin Society. 



When ordinary Fl agouti rabbits were mated with themselves, their 

 progeny were agouti, black, yellow, and tortoise, in the ratio 9 : 3 : 3 : l.i 

 This shows that there are at least two pairs of factors operating, and, 

 representing them meantime by " unknown " symbols, we can set down the 

 colours and their factors thus : — 



Agouti. 

 X 

 Y 



9 : 



Agouti results with the concurrence of X and Y, black with X and //, 

 yellow with x and Y, and tortoise with x and y. 



This finding is confirmed elsewhere in the experiments thus : — 



(1) When tortoise was mated with tortoise, tortoises only were produced.^ 



(2) When heterozygous yellow was mated with tortoise, only yellows and 



tortoises were produced.' 

 When heterozygous yellow was mated with itself, only yellows and 

 tortoises were produced."* 



(3) When pure black (Himalayan) was mated with tortoise, the first 



crosses were all black/ and the second black and tortoise in the 

 ratio 3 : l.« 

 When pure black was mated with heterozygous yellow, blacks and 

 agoutis were produced in the ratio 1:1.' 



(4) When heterozygous black was mated with tortoise, blacks and 



tortoises were produced in the ratio 1 : 1.' 

 When heterozygous black was mated with pure black, blacks only 

 were produced.'' 



But from one mating of black and heterozygous yellow there resulted a 



black male (No. 28), which bred in an extraordinary manner. Had his 



Xx 

 constitution been wliat is usually expected from such parents, viz., ^ , he 



should have thrown blacks and tortoises from ordinary Fl blacks in the 

 ratio 3:1; instead of which he threw agoutis, blacks, yellows, tortoises, and 

 agouti-black — a new colour — in tlie ratio 1:4:1:1:1;^° while, from tortoises, 

 he should have thrown blacks and tortoises in the ratio 1:1: instead of whicli 

 he threw, from a single doe, three blacks, one yellow, and two tortoises." 

 From these results we can at once infer part of the constitution of this 

 black rabbit. Since lie threw tortoises from ordinary Fl black and tortoise, 



1 Journal of Genetics, vol. ii, 1912, p. 224. ^ ^jj^^, p. 223. ^ Ibid. p. 223. * Ibid. pp. 223 

 and 229. ^ jUd. p. 223. « Ibid. p. 224. ' Ibid. p. 223. » Ibid. p. 224. "> Ibid. p. 224. 

 i» Ibid. p. 226. !'■ Ihid. p. 234. 



