DARWINISM DEFENDED. 133 



cell of any particular single kind has. Thus one kind of 

 determinant represents all the attributes of the red blood 

 corpuscles, another of the nerve-ganglion cells, another of a 

 certain type of epithelial cells, and so on. Each determinant 

 has also the power of assimilating food, growing and re- 

 producing itself by division. Now the possibility of repre- 

 senting in the germ-plasm the nearly infinite capacity to 

 vary characteristic of this plasm has for its physical or 

 mechanical basis the minute size of the biophors and deter- 

 minants coupled with the inconceivably many combinations 

 of different kinds of biophors possible in the make-up of the 

 determinants which are, as already said, the actual structural 

 representatives of, or better, controllers or producers of, 

 the various kinds of body tissue and organs. 



These three general assumptions of Weismann, 8 namely, 

 ( i ) the composition of germ-plasm out of ultimate life-units 

 called biophors (grouped into determinants) which deter- 

 mine all the physical characteristics of the individuals into 

 which the germ-plasm develops; (2) the isolation (from the 

 soma) and the continuity (from generation to generation, 

 from beginning to end) of the germ-plasm; and (3) the 

 Allmacht of natural selection, which involves the discarding 

 of all other factors of modification and species-forming than 

 the natural selection of the slight fluctuating congenital 

 variations produced (in an unknown manner) by infinitesi- 

 mal changes in the determinants of the germ-plasm these 

 three fundamental and important Weismannian assumptions, 

 accepted more or less nearly completely by Wallace and a 

 . number of other English biologists, and by a 

 ismandNeo- few naturalists of Europe and America, con- 

 amarckism, s titute the essential position of what is called 

 neo-Darwinism. This neo-Darwinism immediately found 

 many capable antagonists, and as most of the antago- 

 nists were believers in some parts of the general theory 

 of adaptation and species-forming first proposed by 



