246 MK. J, T. CUNNINGHAM ON 



occurs in all those that have a crest, both males and females, 

 although the comb is much smaller in the hens. The two 

 specimens without a crest, on the other hand, No. 1 (^ and 

 No. 7 2 ; have the normal rose comb with a projecting point 

 behind. The crest makes no difteience to the shape of the single 

 comb. There is thus a correlation between the crest of featheivs 

 and the truncated trifid character of the rose comb : these two 

 characters either occur together or are absent togethei'. I believe, 

 however, that this is not a coupling of two distinct characters 

 but that they are both manifestations of one character. What 

 Bateson calls a. trifid element is in my opinion nothing but the 

 crest ; the factor which causes the development of the crest of 

 the feathers also causes the posterior truncation of the comb. 



The most remai'kable and interesting result in my experiment 

 is the condition of the recessive whites in the first brood of F.,'s. 

 Both of these whites show some colour, while according to the 

 Mendelian theory of segregation they ought to show none. The 

 specimen No. 1, now (Sept. 30, 1911) 4^ months old and in 

 mature plumage, has a band of colour across the back behind the 

 shoulder ; when I first noticed this colour it was a very pale 

 yellowish tinge, so slight that it was difficult to be sure that it 

 was actually pigment in the feathers and not accidental staining. 

 Now it is darker and more orange, and there is also a slight 

 yellow tinge in the neck hackles. The other white, No. 2, has also 

 some slight colouidng, a faintly tinted region on the back like 

 the other, and some veiy pale patches on the neck venti'ally 

 and over the eye on each side. These Avhite specimens weie 

 yellowish white in the down when first hatched, but this is no 

 evidence of colour, for the dow'n of the chicks of Avhite fowls, as 

 of white ducks, is always yellowish. The two whites of the 

 second brood do not yet show an}^ colour. 



Now this fact shows that the Mendelian doctrine of complete 

 segregation and gametic purity is not always true. The fact 

 that these recessive whites do appear in the F„ generation shows 

 clearly that gametic segregation does take p)lace in the F, 

 individuals, but in my experiment the recessive white is not 

 exactly the same as the original white of the Silky : it is no 

 longer pure, but is mixed with a little of the colour factor with 

 Avhich it has been inixed in F,. "VVe must consider whether the 

 result obtained by me is explained in any degree by Bateson's 

 conclusion concerning the white of the Silky. As already men- 

 tioned, he concludes that this wdiite is due not to the absence of 

 all colour factors, but to the absence of one out of two which 

 together produce colour. Now this partial colour factor cannot 

 explain my i-esult, for it cannot by itself produce any colour, and 

 the essential point of the Mendelian doctrine is that the recessive 

 individual in F., is homozygous, i. e. due to the union of two 

 gametes each of wdiich carries the factor for the recessive 

 character. The recessive chaiacter in the case under considera- 

 tion is the white of the Silky, and the white in the indiAidualb 



