No. 515] NOTES AND LITERATURE 703 



Darwin. A black tail bar was present and the wing coverts 

 and back were of a smoky black color, obscuring the wing bars 

 which are common to the rock pigeon. The reversionary type 

 in some cases appeared in the F 1 generation. A similar result 

 was obtained by Darwin in the F t generation from a Nun and a 

 red Tumbler. 



The author explains the fact of the reversionary blue not 

 appearing until the F 2 generation in the Barb X Fantail cross, 

 by assuming that the F 1 individuals contain some element which 

 prevents the appearance of blue. This, he holds, is the factor 

 for black self color, which is epistatic to blue. In the recom- 

 bination of factors in F 2 , those combinations containing blue 

 without the black factor produce individuals with blue feathers, 

 while those with the black factor exhibit black feathers but no 



Reference is made to other cases of reversion (sweet Peas and 

 Stocks) in which its occurrence is due to the meeting of com- 

 plimentary factors. He adds, "In the case of the Barb X Fan- 

 tail cross the evidence is not yet sufficient to show whether the 

 factors needed to produce the atavistic condition are all present 

 in the Barb and their effect merely hidden by the presence 

 of the black factor, or whether a necessary factor is introduced 

 by the fantail ; but the fact that no blues came in the F 2 made 

 from an F, (Barb X Fantail) X *\ (Barb X Nun) distinctly 

 suggests that some factor of the blue did come from the Fantail." 



The general result of the Barb X Fantail experiments shows a. 

 dominance of black and blue to white. This dominance, how- 

 ever, is imperfect, as the majority show some white feathers. In 

 the F 2 generation from such crosses, the following types were 

 obtained : 



Black. 



Black with some white feathers. 

 Blue. 



Blue with some white feathers. 

 Red. 



White with some colored feathers. 

 White. 



The significance of the presence or absence of the white 

 feathers is obscure. It was first thought that the white feathers 

 indicated that the bird was producing white-bearing gametes. 

 This is not true in all cases. 



