176 ANIMAL LIFE AND HUMAN PROGEESS 



tration I choose some experiments with poultry carried out 

 by the late Major P. G. Bailey and myself. "We crossed the 

 Sebright bantam with one of the smaller full-sized breeds, the 

 gold-pencilled Hamburgh. Roughly speaking, the Hamburgh 

 is about double the weight of the Sebright. The first-cross 



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Fio. 8. — Diagram showing the experimental results obtained by crossing 

 silver Sebright bantams with a gold-penoiUed Hamburgh cook. Since in 

 poultry the hen is always Ughter than the cock, the F^ hens have been 

 " weighted," i.e. multiplied by a constant factor (found experimentally), to 

 bring their weights up to those of the corresponding cocks. In the Fj 

 generation the records of the cocks only are shown. A similar result was 

 obtained for the hens. 



birds were intermediate in size, though they approximated 

 more closely to the larger Hamburgh (Fig. 8). Bred 

 together they gave rise to an Fg generation ranging from 

 birds smaller than the Sebright to birds larger than the Ham- 

 burgh, the majority, as the curve shows, being intermediates of 

 various weights. 



