THE GERM-PLASM THEORY 281 



constitutes an id. So far Weismann's hypothesis is in 

 close agreement with the idea of representative particles 

 which we are driven to adopt by the facts of Mendelian 

 inheritance, except that, following de Vries, we should 

 speak of separate characters rather than parts as 

 being thus represented ; for there seems to be no doubt 

 that the same character-determinant can affect the 

 development of a number of different parts. But at 

 the next step the Mendelian parts company with 

 Weismann. The latter assumes that the cells of an 

 organism contain a large number of ids, or complete 

 sets of determinants, half of the total number being 

 derived from either parent, and that, although at the 

 reducing division which precedes the formation of the 

 gametes the total number of ids is reduced to half of 

 what it was in the somatic cells, still several ids 

 derived from each parent are present in every germ- 

 cell. 



Thus the reduced number of chromosomes in the 

 germ-cells is regarded as containing all the primary 

 constituents of both parents. And it is an essential 

 point in Weismann's theory that he regards a given 

 germ-cell as containing a considerable number of ids 

 derived from its ancestors, all near ancestors being 

 thus represented. 



But Mendel's experiments and others of the same 

 kind show, in the case of a great number of different 

 characters, that although every essential character is 

 represented in every germ-cell, yet each Mendelian 

 character is represented by a paternal or a maternal 



