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THE AMERICAN NATURALIST [Vol. XLIX 



sity is inherited independently of the agouti factor as 

 crosses with dilute colored varieties of rabbit show. For 

 a cross between black-and-tan and blue produces in F 2 

 (1) blue-and-tans as well as (2) black-and-tans, (3) blacks, 

 and (4) blues. This result is strictly parallel with that 

 obtained by crossing intense gray rabbits with blue ones. 

 In that case there are produced (1) blue gray, (2) intense 

 gray, (3) black, and (4) blue young in F 2 . It is evident 

 that in each case a dihybrid cross is made and that the end 

 products are the same in the two series except for the dif- 

 ference in the agouti marking of varieties (1) and (2). 

 The natural conclusion is that black-and-tan contains an 

 alternative form of agouti to that found in gray rabbits. 

 If so, it should be capable everywhere of substitution for 

 gray, wherever the latter occurs throughout the entire 

 series of color varieties, and indeed this appears to be the 

 case. 



That the black-and-tan factor, like the- ordinary agouti 

 factor, is independent of the extension-restriction pair of 

 allelomorphs is shown by a cross of black-and-tan with 

 sooty yellow (i. e., non-agouti yellow or "tortoise"). 

 F 2 contains (1) black-and-tan, (2) black, (3) yellow 

 ("fawn"), and (4) sooty yellow ("tortoise") young. 

 The first two are varieties with extended pigmentation, 

 and the second two are varieties with restricted pigmen- 

 tation; further, varieties (1) and (3) contain modified 

 agouti, but varieties (2) and (4) do not. 



If a gray rabbit had been used, instead of a black-and- 

 tan, in making the cross just described, three of the four 

 varieties obtained in F 2 would have been indistinguish- 

 able from those enumerated, and the fourth one would 

 merely have been gray instead of black-and-tan. This 

 supports the view that black-and-tan is merely an alterna- 

 tive form of gray. 



Further, we have evidence to show that the black-and- 

 tan form of agouti, like the agouti of gray rabbits, is inde- 

 pendent of the genetic factors which respectively produce 

 Dutch pattern, English pattern, and angora coat, since we 

 have been able to produce individuals in which black-and- 



