252 MR. J. T. CUNNIXGHAM ON 



and Punnett crossed the Silky with specimens of a certain strain 

 of Brown Leghorns in their possession. When the SiU^y hen was 

 mated with the Brown Leghorn cock, the F^ chicks, instead of 

 being strongly pigmented as in the experiment 1 have described, 

 were scarcely pigmented at all. It appears at first sight as if in 

 the Silky x Bankiva cross the pigmentation is dominant, while 

 in the Silky-Leghoi-n the same character is recessive. Many of 

 the F^ chicks were reared, and in the adult state wei-e almost 

 indistinguishable in general appearance from pure unjDigmented 

 birds. Thus these F^ birds were in appearance similar to the F., 

 recessives described by me, though in constitution they were 

 very different. I shall have to return to this point later. 

 Careful examination of the F/s in Bateson and Punnett's 

 experiment showed traces of pigmentation. These are described 

 as sometimes patches on the wattles, skin, or shank ; pigment 

 was also often found in the joeriosteum of the femoro-tibial or 

 tarso-metatarsal joints and frequently in the peritoneum. No 

 mention is, however, made of pigmentation under the skin of 

 the abdomen or on the wing-joints as in my F, recessives. 



On the other hand, when the reciprocal cross was made, namely 

 Silky cock with Brown Leghorn hen, the results were markedly 

 different : the males were like those of the first cross, but the 

 females were all deeply pigmented. It might be said that in this 

 case the pigmentation was dominant in the females, recessive in 

 the males, while when the Brown Leghorn was the male parent 

 the pigmentation was i-ecessive in both sexes. It is certainly 

 remarkable to meet with such a sexual difference as this in a 

 character which showed no signs before the crosses were made of 

 being in any way sexual. No such sexual difference in the F/s has 

 been found to occur in the cross with which I have experimented, 

 or in crosses with the Silky described by other naturalists. In 

 all other ci^osses known the F^'s were deeply pigmented ; and 

 Bateson and Punnett point out that the almost coujplete absence 

 of pigmentation in one or both sexes of the F/s in their case is 

 related to the fact that the Brown Leghorns used by them had 

 unpigmented shanks, while most breeds normally have pigment 

 in the skin of the shanks, as in the Gcdlus hanliva described 

 above. 



Bateson and Punnett explain their results as due to the 

 segregation of three pairs of hypothetical factor's, namely, P, p, 

 presence and absence of pigmentation, I, i, presence and absence 

 of a factor which inhibits the development of the pigmentation, 

 and F, f, presence and absence of femaleness. It may be 

 noted here as an instance of the difficulty of keeping pace with 

 Mendelian theories, that Bateson seems to have already 

 abandoned his former theory of sex according to which maleness 

 and femaleness were alternative to each other, for he now 

 suggests that there may be another pair of charactei'S, presence 

 and absence of maleness. The inhibition factor I is supposed to 



