THEORIES OF HEREDITY 71 



For instance, in two related varieties of butterflies a certain 

 spot on the wing may be in the one variety of a brown 

 colour, in the other red. The determinants, though homol- 

 ogous in both cases, will tend to impart a different colour 

 to that special spot on the wing : they will be, as Weismann 

 has expressed it, " heterodynamous " in their action ; 



A. IB. 'C 



FIG. 40. BLENDED INHERITANCE IN LEAVES OF WILLOW. 



(From J. A. Thomson, "Heredity.") 

 A and C, the two parents ; B, the hybrid offspring. 



while determinants impressing the same quality on any 

 given part of the organism would be " homodynamous " 

 in their effect. 



Now, as the development of any cell during ontogenesis 

 is determined by only one kind of determinants of the 

 germ-plasm, and as in amphimixis homologous deter- 

 minants of the father and mother organism unite, it is the 



