182 MR. J. T. CUNNINGHAM ON RESULTS OF A 



All this is, of course, regardless of the hypothesis that the 

 colour in itself is due to two separate factors, X & Y. The third 

 of the above fertilizations iin})]ies that the factor for daikness 

 might be carried by tlie lecessive without the factor for colour. 

 If so, light-coloured birds mated with ])i\e might produce da.rk- 

 coloured offspring. I have not obsei'ved such cases in my results. 

 On the other hand, anothe}- possibility is perhaps worth con- 

 sidering — namely, that the factor determining the darker colour 

 is only quantitatively different from that causing the lighter. 

 The darker colour onai/ be due to an additional colour-factor 

 segregating separately. Thus, if we substitute Cc for Dd in the 

 above scheme, we shall have as the offspring of a dark-coloured 

 bird mated with i-ecessive, OCcc, 2 Occc, cccc — in other words, 

 dark, light, and recessive in the proportions 1, 2, 1 instead of 

 1, 1, 2. Which of these agrees better with the actual results of 

 experiment, the numbers reared by me were too small to decide. 



Pigmentation of Skin. 



In my previous paper I described the occurrence of a certain 

 amount of pigmentation in the skin and internal membranes of 

 one of the birds otherwise recessive for this chai'acter — namely, 

 F^ II 2 c?. In subsequent generations this impurity of the 

 recessives with respect to this char-acter was constantly observed, 

 the amount of pigmentation varying in different individuals, in 

 some cases being greater than in the F„ generation. Thus, in 

 F3 IV 2 $ , which died on October 14th when about 5 weeks old, 

 the skin of the abdomen was dark, almost black, lighter oA'er 

 sternmn, dark again over crop and ventral side of neck. There 

 was a good deal of pigment round the eye and on lower eyelid. 

 The shoidder-joint, elbow-joint, and wrist-joint appeared almost 

 black on dorsal side, and the bones of the leg and wing weie 

 dark. Slight pigment was visible in the peritoneum over the 

 gizzard, but none in or on the ovai-y. 



In Fjl, of six chicks five were recessive in skin-pigmentation 

 and one pigmented. In all the recessives there was pigment in 

 the skin of the abdomen and round the eye. F^IY 1 $ and 

 FjIV 25 were killed in KSeptember, 1913, and I skinned them 

 after cutting the feathers short to show the surface of the skin, 

 but the dry skins now do not show the pigment distinctly, as it 

 was in the fresh state. I noted from the examination of 

 F^IV 2$ immediately after death that the abdomen was quite 

 dark, and that the pigment was not only in the skin and 

 peritoneum but in the connective tissue of the abdominal wall. 

 There was pigment over the gizzard, the oviduct on the left and 

 the vestigial right oviduct were conspicuously black, and also the 

 ureters appeared as black streaks. 



In the later generations all the recessives had pigment in the 

 abdomen. It is clear that in this character, as in that of 

 phimage- colour, pure recessives and therefore complete segrega- 

 tion did not occur, and also that although individuals varied the 



