R. C. PUNNETT AND M. S. PeASE 



•239 



When both of these inhibitors are present they lead to the formation of 

 a white bird. Such a condition arises when a silver ^ is mated with a 

 chamois % . Assuming both parents to be homozygous it is clear that 

 all of the offspring would be heterozygous for each of the inhibitors, 

 and would consequently all be white. We have not actually realised a 

 cross in which all the offspring were white. In Exp. (3) about half of 

 the offspring were coloured, but this, as we have already pointed out, 

 we regard as due to the accident of our chamois $ having been hetero- 

 zygous for the inhibitor of melanic pigment. The chamois </ used in 

 Exp. (4) was however homozygous, and all of the progeny lacked melanic 



a b c 



Fig. 1. 



pigment except for occasional ticks. But owing to the fact that the 

 silver $ is heterozygous for the gold inhibitor the <f(f alone from this 

 cross are white, the pullets being chamois. 



Here we may mention a point of some interest which has arisen in 

 connection with our whites. Though at first fully white, except for a 

 few dark ticks, the}^ shew indications of very faint barring as they gi'ow 

 older. We have observed this in all of the whites we have bred — which, 

 of course, were all heterozygous — though the barring is rather more 

 distinct in some than in others. Mr Lewis Jones tells us that he has 

 also observed this " ghost " barring in birds similarly bred by him, and 

 he kindly sent us several to compare with our own. Whether the "ghost" 

 barring is peculiar to the later feathers, or whether the feather is at 

 first white and subsequently developes the barring on exposure to the 



16-3 



