48 Genetic Studies in Poultry 



The hypothesis of complementary factors. 



In the account of his experiments on the nature of henny cocks, 

 Morgan suggests that the Sebright differs from the normal (in this 

 case, Black-red Game Bantams) in two factors. The presence of both of 

 these factors is assumed to be necessary for the development of henny 

 feathering. This interpretation rests almost entirely upon the pro- 

 portions of henny and normal cocks appearing in the F2 generation, 

 and Morgan points out that the experimental numbers, viz. 31 henny 

 to 28 normal, are far removed from a 3 : 1 ratio but approximate closely 

 to a 9 : 7 ratio. A few birds were bred by crossing F^ with game, and" of 

 these two are recorded as henny and seven as cock-feathered. This again 

 is close to expectation on the hypothesis of two complementary factors. 



We venture to suggest a possible interpretation of Morgan's results 

 which would bring them into harmony with our own, viz. that some of 

 the birds recorded by him as cock-feathered were in reality intermediate 

 birds of the type that shews a marked approximation to normal cock 

 feathering. If a dozen of his 28 F^^ ^ , recorded as normals, were of this 

 type, we should have a close approximation to a 3:1 ratio. We have 

 already pointed out how easily one may classify these cock-like inter- 

 mediates as of normal plumage, unless one is on one's guard. The 

 distinction was forced upon us by the change to henny plumage that 

 occurred at the moult of such birds. Morgan makes no remark about 

 changes in the character of the feathering at moult, and one is led to 

 suppose that his birds were generally destroyed before this stage was 

 reached. We consider that our view is indirectly supported by the state- 

 ment that Morgan makes with regard to intermediates. He recognises 

 such birds among his Fg cTc/, but states that "the line between inter- 

 mediate and cock feathering is sharp, all the intermediates belonging 

 distinctly to the hen-feathered group, but the line between the two 

 subdivisions of hen-feathered birds is not sharp, and occasionally a bird 

 is found that is difficult to place " (p. 15). Unfortunately we are given 

 no illustrations of the feathers of these intermediate birds, but it is 

 evident from the account that they approximated to the full henny 

 condition, and perhaps resembled such birds as the one whose feathers 

 we have figured on PI. VII, fig. 3. 



We may add that we have examined our own data carefully on 

 the supposition that two complementary factors might be concerned 

 with henny feathering, but find no grounds for supposing such to be 

 the case. In our experiments, which involve a far greater number of 



