458 THE GERM-PLASM 



the half. The reduction is important in elucidating the phenom- 

 ena of heredity in forms which are reproduced sexually, for the 

 ids of a germ-plasm are not by any means all alike, but dilTer 

 to the same relative extent as do the corresponding individuals. 

 As the reduction does not always occur in the same way, and 

 the resulting halves contain different idants on different occa- 

 sions, and these fall to the share of individual germ-cells, it is 

 possible for the germ-cells of one individual to contain very 

 different combinations of idants. This results in the dissimi- 

 larity between the offspring of the same parents, — or, to express 

 it in more general terms, in the extreme diversity as regards the 

 intermixture of individual differences. 



During the development of a new individual from the fertilised 

 egg-cell, the ontogeny is directed by the ids of the two parents 

 which constitute the germ-plasm. Structures intermediate 

 between those of the parents thus frequently arise — but only 

 when perfectly homologous ids are opposed to one another, 

 and have a similar 'controlling force.'' This force depends 

 not only on the similar rate of multiplication of the biophors 

 transmitted by the controlling determinants into the cell-body, 

 and on the suppression of those already present, but also on the 

 number of precisely similar determinants derived from each 

 parent. The larger the number of ' homodynamous' deter- 

 minants, the greater is their controlling effect on the cell ; and 

 if a larger number of homodynamous determinants are opposed 

 to fewer heterodynamous determinants of the other parent, the 

 former gain the victory. The preponderance of one of the 

 parents in transmission is thus rendered comprehensible, whetlier 

 it concerns individual parts or the entire organism. 



The type of the child is determined by the paternal and 

 maternal ids contained in the corresponding germ-cells meeting 

 together in the process of fertilisation, and the blending of 

 parental and ancestral characters is thus predetermined, and can- 

 not become essentially modified by subsequent influences. The 

 facts relating to identical twins and to plant-hybrids prove that 

 this is so. In the latter, the individuals produced by crossing two 

 constant species display as constant an intermixture of charac- 

 ters as would be the case if they constituted a natural species. 

 The ids of each species must be looked upon as perfectly 

 homodynamous as regards the specific characters ; two distinct 

 groups of homodynamous ids are opposed to one another, and 



