R. C. PUNNETT AND P. G. BaILBY 39 



crossing strains of animals or plants of similar size is not due to in- 

 creased vigour resulting from the cross, but to the bringing together 

 of independent gi-o\vth factors each capable of producing some effect. 

 Were this the case it would be apparent in the Fo generation where 

 fixable strains both larger and smaller than the parent forms should 

 make theii' appearance. 



In conclusion we may once more state that the scheme which we 

 have put forward is a tentative one and may have to be recast in any or 

 all of its details in the light of futuiv knowledge. Nevertheless there 

 can be little doubt that it expresses an essential truth in connection 

 with the inheritance of the complex character designated weight. The 

 facts of breeding offer a clear indication that weight may depend upon 

 the presence or absence of definite genetic factors segTegating from one 

 another in sametooenesis on lines with which students of these matters 

 are already familiar. 



The experiments of which an account is given above form part of a 

 series of investigations on heredity in poidtry for which the means have 

 been provided out of the Fund controlled by the Development Com- 

 mission. 



EXPLANATION OF PLATE IV. 



In all six figures the birds are taken to the same scale. 



Fig. 1. Gold Pencilled Hamburgh s and Silver Sebright ? . 



Fig. 2. ,, ,, I? and t'l s ex Silver Sebright x Gold Hamburgh. 



Fig. 3. ,, ,, ? and Fi ? ,, „ 



Fig. 4. Silver Sebright ? and h\ ? ex Silver Sebright x Gold Hamburgh. 



Fig. 5. Small FoS (Pen 13, 1913) and Large F.,.l (Pen 12, 1913). 



Fig. 6. „ F.f ( „ ) „ t\-i ( „ )■ 



