W. Batbson and R C. Ptjnnett 191 



normally homozygous aod the hea heterozygous for this factor. Con- 

 stitutionally therefore we look upon the cocks and hens of this breed 

 as being respectively fflipp and Ffll-pp. To illustrate what we 

 imagine to happen in the several generations produced by mating 

 a Silky (/" with a Brown Leghorn $ as well as in the reciprocal cross 

 we have drawn up the appended schemes (Figs. 3 and 4) for comparison 

 with Figs. 1 and 2. These schemes also indicate the composition on 

 our hypothesis of the generations shown and we may now proceed to 

 test their validity by the facts witnessed in these and other forms of 

 mating. 



Detailed results of the various crosses. 



1. The fj generation. 



(a) From the Silki/ $. 



[Nature of mating FfPPiixffppIL] 



We have bred from Silky % x Brown Leghorn </ on two occasions 

 and in neither case had any of the chicks more than a slight amount 

 of pigment (cf. Fig. 1). Many of these were reared and in the adult 

 state were almost indistinguishable in general appearance from pure 

 unpigmented birds. Careful examination however revealed traces of 

 pigment as patches either on the wattle, skin, or shanks. In most 

 cases the presence of some pigment was most readily detected beneath 

 the skin in the periosteum of the femoro-tibial or of the tarso-metatarsal 

 joints. Dissection showed that some pigment was nearly always present 

 in the ribs and in the occipital region of the skull. There was frequently 

 a little peritoneal pigment more especially in the region of the ribs 

 and some in the occipital pia mater. The amount of pigment varies 

 somewhat and may be very slight. In some cases the chicks are 

 recorded in our notes as being without pigment, but most of these 



