1 86 Sex-limited hiheritance [ch. 



The above tabulation represents so well the main outline 

 of the results of experiment that it is probably a close 

 approximation to the truth. With regard to the somewhat 

 meagre results of the other matings it may be said that, as 

 far as they go, they are fairly consistent with the schematic 

 representation, though some discrepancies occur, and un- 

 questionably much remains still to be cleared up in this 

 remarkable case. The distribution of the several factors 

 among the gametes of the two types of F^ females cannot 

 yet be satisfactorily represented, and there is some evidence 

 that the repulsion between femaleness and D is not always 

 so complete as the scheme demands. 



In introducing the evidence as to Silkies attention was 

 called to the fact that the difference between reciprocal 

 matings occurred when the non-pigmented parent was of a 

 breed which had unpigmented shanks. There are of course 

 many breeds which though they have nothing corresponding 

 to the general pigmentation of the Silky, are black or bluish 

 in the shanks from a deposition of black pigment in the skin 

 of that part"^. When such hens are crossed with the Silky 

 cock the pigmentation is developed not only in the female 

 offspring, but also in the males. Davenport made crosses 

 between Silkies and Spanish (black-shanked) and Frizzles 

 (slaty shanks), and found no distinction between reciprocal 

 matings, both sexes of the offspring being deeply pigmented. 

 We crossed white rose-combed Bantam hens with a Silky 

 cock with the result that the F^ males and females were 

 both deeply pigmented on hatching, though as they became 

 adult the males lost much of their pigmentation. The white 

 rose-comb is slightly bluish in down-colour and the shanks 

 are slightly pigmented in varying degrees. 



From many signs we know that there exists some com- 

 plex relation between the colour of the shanks in fowls 

 generally, and sexual differentiation. Some years ago we 

 described (19, p. 95) a case of this kind in which Indian 

 Game % x White Leghorn t always gave F^ yellow-shanked 

 like both the parent breeds. But White Leghorn % x Indian 

 Game t gave cocks yellow-shanked like the parents, while 



* This pigment is confined to the skin. There is none in the 

 periosteum. When the general skin-colour is yellow these pigmented 

 shanks have a greenish tinge, the "willow" of fanciers. 



