R. C. PlTNNETT AND THE LATE MaJOR P. G. BaILEY 53 



We may however recall that certain human defects present analogous 

 features in their heredity. Night-blindness may in some families be 

 sex-linked (cf. Newman, 1913), while in others it behaves as an ordinary 

 dominant (cf Nettleship, 1907). And from the data collected by Nettle- 

 ship (1909) on Leber's disease, it would appear that both forms of 

 transmission may occur here also. It seems not unlikely that some 

 of the complications found in such pedigrees may be due to the dual 

 mechanism involved in the transmission of the same factor. There is 

 however a remarkable feature about night-blindness, in that it behaves 

 as a dominant when transmitted equally to either sex ; whereas, when 

 associated with the sex-linked mechanism, its behaviour is that of a 

 recessive. Apart from this peculiarity, and having regard only to the 

 sex-linked cases, there is a further point of difference between the 

 human being and the fowl. From analogy with Drosophila we are led 

 to infer that the sex-chromosome peculiar to the heterozygous sex 

 cannot carry a sex-linked factor. But in the poultry case it is difficult 

 to see how we can avoid supposing that the factor for henny plumage 

 in normal breeds is carried by the sex-chromosome peculiar to the 

 heterozygous sex, in this case the female. Though the human cases 

 resemble the poultry case in shewing both sex-linked and ordinary 

 inheritance, there are clearly difficulties in the way of instituting a 

 closer parallel between them. 



In suggesting the view of henny-feathering outlined above, we have 

 not overlooked the possibility of an interpretation on the lines so ably 

 developed by Goldschmidt for the intersexes in his Lymantria crosses. 

 Such an interpretation, however, implies a different result in the reci- 

 procal crosses between normal and henny breeds ; and this, according to 

 Morgan, does not obtain. Moreover, the only type of intersex produced 

 would be the henny cock, in which comb, wattles, spurs, and sexual 

 behaviour are all as in normal males. It seems unlikely that this single 

 type^ can represent both male and female intersexes. Were we to sup- 

 pose that certain henny cocks were genetically females, i.e. in so far as 

 the sex-chromosomes are concerned, we should look for a considerable 

 excess of females in their progeny from normal hens. Our results from 

 a number of such matings, however, shew that the sexes are produced 

 in nearly equal numbers, i.e. 324 ^ ^^ and 345 $ ? (cf Table I). We 

 incline to agree with Goldschmidt when, in his discussion of henny 

 feathering, he says "Wir mtissen gestehen, dass im Augenblick die 



1 Single, because a given cock may exhibit the extremes at diSerent times in his life 

 history. 



