294 THE WHENOE AND THE WHITHER OF MAN 



be arrested in their growth. It is even possible that 

 the effects of these influences may be more specialized ; 

 that is to say, they may act only upon certain parts of 

 the germ-cells. But this is indeed very different from 

 believing that the changes of the organism which re- 

 sult from external stimuli can be transmitted to the 

 germ-cells and will redevelop in the next generation at 

 the same time as that at which they arose in the par- 

 ent, and in the same part of the organism." 



But if the germ-plasm has this constitution and rela- 

 tion to the rest of the body, how is any variation pos- 

 sible? Different individuals of any species have 

 slightly different congenital tendencies. Hence in the 

 act of fertilization two germ-plasms of slightly differ- 

 ent structure and tendency are mingled. The mingling 

 of the two produces a germ-plasm and individual dif- 

 fering from both of the parents. Thus, according to 

 Weismann's earlier view, the origin of variation was 

 to be sought in sexual reproduction through the min- 

 gling of slightly different germ-plasms. 



But how did these two germ-plasms come to be dif- 

 ferent ? How was the variation started ? To explain 

 this Weismann went back to the unicellular protozoa. 

 These animals are undoubtedly influenced by environ- 

 ment and vary under its stimuli. Here the variations 

 were stamped upon the germ-plasm, and the commin- 

 gling of these variously stamped germ-plasms has re- 

 sulted iu all the variations of higher animals. 



Of late Weismann has modified and greately im- 

 proved this portion of his theory. He now accepts 

 the view that external influences may act upon the 

 germ-plasm not only in protozoa but also in all higher 

 animals. Variation is thus due to the action or stimu- 



