24 On Inheritance of Weight in Po^iltry 



F«. Nevertheless the great i-ange of variation in F.2 suggests an 

 interpretation by means of several segregating factors, though this 

 cannot be decided definitely without raising an F^ generation. Whether 

 size in animals can be expressed in terms of Mendelian foctors is there- 

 fore still an open question. 



The present paper gives an account of some experiments which we 

 have been carrying out during the past few years with the object of 

 learning something about the transmission of weight in poultry. For 

 this purpose two breeds were selected which differed considerably in 

 size, but not sufficiently to prevent natural crossing. At the same time 

 it was considered advisable for reasons of economy that the larger breed 

 used should not be too large ; otherwise it would not have been possible 

 to rear so many oHspring to maturity. The two breeds eventually 

 selected were the Gold-pencilled Hamburgh and the Silver Sebright 

 Bantam. The choice was determined with the idea of following up the 

 inheritance of other characters in addition to size, and in this set of 

 experiments we have been investigating also the inheritance of gold 

 and silver ground colour, and the peculiar assumption of the hen's 

 plumage by the cock which is characteristic of the Sebright. An 

 account of these characters and their inheritance will be given later. 

 For the present we shall confine ourselves to what we have been able to 

 learn from this cross with regard to the transmission of size. More 

 correctly perhaps we ought to .say weight, since our estimation of size 

 depends entirely on the weight of the biid. Generally speaking the 

 bird that looks heavier will be found actually heavier when weighed, but 

 it is not always possible to be certain from appearance alone. A taller 

 but more slender and "leggy" bird will sometimes be fovmd to weigh less 

 than what appears to be a smaller tliough better furnished one. Weight 

 is doubtless a character which dejjends in some degree on structural 

 characters capable of analysis. We have not found it practicable to at- 

 tempt such analysis for the present. Our criterion throughout has been 

 the weighing pan alone. Observations start with the egg weight. The 

 newly-hatched chicken is also weighed, and a record is then taken weekly 

 or fortnightly up to the end of the 35th week. It would of course be 

 desirable to have a complete record of every bird from the day of hatching 

 to the day of natural death. In practice this is not possible owing to the 

 difficulty of keeping so many birds. A bird, especially a cock, may go 

 on growing more than a year after it is hatched. But we have found 

 that such growth, when it occurs, is intermittent. Birds hatched from 

 February to May receive a check in their growth at the end of the year, 



