X] The Silky Foi.ul i8i 



disturbing effects of some other dominant factor unde- 

 termined, which alters the normal distribution of the factors 

 B and ? in the gametogenesis of certain black-eyed hens, 

 but that is mere conjecture. 



Attention must be drawn to the paradoxical conclusion 

 that black-eyed hen Canaries, zvhethei^ green or yellow^ are 

 normally heterozygous in respect of the black-eye character*, 

 being thus in common parlance "hybrids" of Cinnamon! 

 The males, on the contrary, are in general homozygous or 

 pure in the black-eye character. This discovery gives rise 

 to many reflections, some of which will be spoken of after 

 the facts of the next case are described. 



The Silky Foivl 



The example of heredity limited by sex that we are 

 about to consider exhibits a complication which at first 

 sight suggests that the phenomena are the converse of 

 those last detailed. In the Canaries when the two sexes 

 raised from a cross differed from each other it was the 

 females which presented the recessive feature and the males 

 which showed the dominant. We shall here see that when 

 the sexes differ it is the female which ostensibly shows the 

 dominant. Nevertheless the difference is apparent, not 

 real. In the case of the Cinnamon Canary the observed 

 results were due to the combinations of two pairs of factors, 

 while those about to be described are due to the combina- 

 tions of thi^ee pairs. The presence of the third dominant 

 cannot however be told by inspection. Breeding tests alone 

 reveal its existence. 



Mr Punnett and I have been enoag-ed for some years in 

 experiments with Silky fowls. The most interesting results 

 were obtained in crosses between Silkies and certain ordin- 

 ary fowls with unpigmented shanks. 



Silkies are remarkable in many ways, but the peculiarity 

 with which we are here concerned is the intense black 

 pigmentation of the mesoblastic membranes. The perios- 

 teum, pia mater, somatopleure, parts of the splanchnopleure, 

 the sheaths of some blood-vessels, and the connective tissue 



* Miss Durham has so fnr tested 7 yellow hens and 6 green hens, and 

 all of these have thrown pink-eyed hens when mated to pmk-eyed cocks, 

 thus proving their heterozygous nature. 



