8 An Examination of Weismanmsm. 



case of unicellular organisms, why should it have 

 ceased to be so in the case of multicellular ? Weis- 

 mann's answer is, that all the multicellular organisms 

 propagate themselves, not exclusively by fission or 

 gemmation, but by sexual fertilization, where the 

 condition to a new organism arising is that minute 

 and specialized portions of two parent organisms 

 should fuse together. Now, it is evident that with 

 this change in the method of propagation, serious 

 disadvantage would accrue to any species if its sexual 

 individuals were to continue to be immortal ; for in 

 that case every species which multiplies by sexual 

 methods would in time become composed of indi- 

 viduals broken down and decrepit through the results 

 of accident and disease — always operating and ever 

 accumulating throughout the course of their immortal 

 lives. Consequently, as soon as sexual methods of 

 propagation superseded the more primitive a-sexual 

 methods, it became desirable in the interests of the 

 sexually-propagating species that their constituent 

 individuals should cease to be immortal, so that the 

 species should always be recuperated by fresh, young, 

 and well-formed representatives. Consequently, also, 

 natural selection would speedily see to it that all 

 sexually-propagating species should become deprived 

 of the aboriginal endowment of immorality, with the 

 result that death is now universal among all the 

 individuals of such species — that is to say, among 

 all the metazoa and metaphyta. Nevertheless, it is 

 to be remembered that this destiny extends only to 

 the parts of the individual other than the contents 

 of those specialized cells which constitute the repro- 

 ductive elements. For although in each individual 



