R. C. PUNNETT 233 



Eight of the agouti-blaek does were also crossed with a pure tortoise 

 buck (j/* 74), and the uumbers obtained, 51 black and 15 agouti, tally 

 closely with the expected 3 : 1 ratio. 



It may therefore be fairly claimed that the constitution of the F-, 

 generation from ^ 28 as tested by further breeding from them is in 

 accordance with the hypothesis framed above. 



The Synthesis of agouti-bearing blacks. 



So far the evidence that a rabbit, visibly pure black, can carry the 

 agouti factor rests entirely upon a single individual — the Fi ^ 28. 

 But if our hypothesis is correct, there should be no difficulty in synthe- 

 sising the agouti-bearing black from the material to hand, and as a 

 matter of fact this has actually been done within the past year. 

 Reference to Fig. 3 (p. 232) shews that of the five blacks resulting from 

 the mating of agouti-black with yellow three carry the factor A, two 

 being heterozygous and one homozygous for that factor. Neither of 

 the two remaining blacks carries A. The simplest way to find these 

 blacks would be to test them by crossing with a pure black of the 

 constitution ddEEaa. As however I had not such an animal ready 

 to hand, I used for testing purposes a chocolate J" which had previously 

 been shewn to be homozygous for E, but to contain neither D nor A^ 

 In this way 13 black does ex agouti-black x yellow have been tested, 

 with the result that three proved to be homozygous for A, four proved 

 to be heterozygous, while in the remaining six A was absent. The 

 details are given in Table IX. 



' For a further account of this animal see later, p. 235. 



