MRXDEMAN EXPKRIMEXTS WITH FOWLS. 253 



be homozygous in the male Brown Legliorn, hetei'oz^-gous in tlie 

 female, and the pigmentation factor to be homozygous in both 

 sexes in the iSilky. With regard to sex a further assumjjtion is 

 made, namely, that when an individual is heterozygous for both F 

 and I, these two in segregation cannot pass into the same gamete, 

 as there is a repulsion between them. The female, moreover, is 

 considered to be always heterozygous for femaleness, while the 

 male is homozygous for the absence of this factor. All these 

 factors being assumed, whether any real meaning can be attached 

 to them or not, their segregation according to the Mendelian 

 theory is shown to pi'oduce results which agree approximately 

 with those observed. But the approximation is not very close, 

 there are many serious discrepancies between the expected and 

 the actual results. 



The next point to be considered is the nature of the inhibition 

 factor in tlie Brown Leghorn. We have seen that the ditlerence 

 between this breed and others, such as Gallus ba/ikica, with 

 regard to pigmentation, is that in the latter the skin of the 

 shanks is pigmented, while in the Leghorn they are unpigmented. 

 The difference, then, is in the degree of pigmentation. Why 

 should the less degree of pigmentation be called an inhibition 

 factoi- ? It may be said it does not much matter what tei'm is 

 used so long as we agree as to the facts. But there is more 

 here than a mere difference of tei-ms. Bateson and Punnett 

 assume that the inhibition factor forms a pair of factors segre- 

 gating independently of the pigmentation factor and its absence. 

 1 see no justification for this. It seems moi'e pi'ol table that the 

 unpigmented character is alternative or allelomorphic to the 

 pigmented, and in Fj is dominant in the case of the Brown 

 Leghorn because it is of a higher degree than in breeds with 

 pigmented shanks. It is interesting to note that in Reptiles, 

 which lepresent the ancestors of Birds, pigmentation in the skin 

 and internal connective tissue is of genei'al occurrence. It would 

 seem, then, that in birds generally the pigment was transferred to 

 the feathers and disappeared from the skin and interior of the 

 body, but remained in the skin of the shanks, which is still, 

 excepting those few species and breeds which have feathered legs, 

 in the reptilian condition covered with epidermic scales. In the 

 Brown Leghorn fowl this last remnant of the internal pigmen- 

 tation has disappeared. But thei'e is no evidence of a distinct 

 factor inhibiting the development of pigment. Thei-e is no more 

 reason for assuming the existence of such a factor in a bird with 

 unpigmented shanks than in one in which the shanks, but not the 

 rest of the body, are pigmented. In the latter case Bateson and 

 Punnett admit that the unpigmented condition is x-ecessive to the 

 pigmentation of the i^ilky, and it is obviously more reasonable 

 and moi-e scientific to regard the condition of the Brown Leg- 

 horn as merely a higher degree of the unpigmented charactei-. 

 Such a higher degree would naturally imply that there is a 



