PHYSICAL CHARACTERS IX MAN 31 



Two earlier studies by Punnett and Bailey (191 4, 

 191 8) on the inheritance of weight in poultry and in 

 rabbits also bear directly on this question. They 

 crossed Gold-pencilled Hamburgs with Silver Sea- 

 bright Bantams. The F^ was not quite so large as 

 the larger parent, while in F, and F3 the range of 

 variation is beyond that of either parent — i.e., both 

 larger and smaller birds w^ere obtained. The results 

 were explained on the assumption that four factors 

 affecting weight were present, two of them being 

 assumed to give an increase of 38 per cent, in a 

 single dose or 61 per cent, when present in the homo- 

 zygous condition. The other two factors were 

 assumed to give 25 per cent, increase in weight in 

 the simplex condition, and 30 per cent, in the duplex 

 condition. The results are believed to give a clear 

 indication that weight in poultr}^ may depend on the 

 presence of definite segregating genetic factors, and 

 it is suggested that the increased size of some hybrids 

 is not due to hybrid vigour, but to the bringing to- 

 gether of independent growth factors. 



In their later study of weight in rabbits, Punnett 

 and Bailey (191 8) made crosses between the large 

 Flemish rabbit and a mixed strain of Himalayan- 

 Dutch-Havana of nearly uniform size. They also 

 made certain crosses betw^een Flemish and Polish 

 rabbits. After making a careful study of the curves 

 of growth in these rabbits, they conclude that " though 

 animals belonging to large breeds may mature more 

 slow^ly than those belonging to small breeds, it does not 

 follow that age of maturity is closely correlated with 

 size." The very small Polish rabbit is believed to 

 mature a good deal more slowly than a larger form such 

 as the Dutch, and the conclusion is reached that size 

 and early maturit}' are to some extent transmitted 

 independently. These conclusions are contrary to 

 the view of Castle, who finds, from a stud}' of growth- 



