24 An Examination of Weismannism. 



should be immortal ; seeing that, if they continued 

 to be so, all species of sexually-reproducing organisms 

 would sooner or later have come to be composed of 

 broken-down and decrepit individuals. Consequently, 

 in all sexually-reproducing or multicellular organisms, 

 natural selection set to work to reduce the term ol 

 individual lifetimes within the narrowest limits that 

 in the case of each species were compatible with the 

 procreation and the rearing of progeny. Nevertheless, 

 in all these sexually-reproducing organisms the 

 primitive endowment of immortality has been re- 

 tained with respect to their germ-plasm, which has 

 thus been continuous, through numberless genera- 

 tions of perishing organisms, from the first origin of 

 sexual reproduction till the present time. Now, it 

 is the union of germ-plasms which is required to 

 reproduce new individuals of multicellular organisms 

 that determines congenital variations on the part of 

 such organisms, and thus furnishes natural selection 

 with the material for its work in the way of organic 

 evolution — work, therefore, which is impossible in 

 the case of unicellular organisms, where variation 

 can never be congenital, but always determined by 

 the direct action of surrounding conditions of life. 

 Again, as the germ-plasm of multicellular organisms 

 is continuous from generation to generation, and at 

 each impregnation gives rise to a more or less novel 

 set of congenital characters, natural selection, in 

 picking out of each generation the congenital char- 

 acters which are of most service to the organisms 

 presenting them, is really or fundamentally at work 

 upon those variations of the germ-plasm which in 

 turn give origin to these variations of organisms 



