THE GERM-PLASM THEORY 279 
which every part of the organism is thus represented 
constitutes an td. 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 tds, 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 
