44f ORGANIC EVOLUTION — PHYSICAL 



cence and revitalization," without which, death must 

 occur, is utterly disproved, as is also the theory that the 

 purpose of conjugation is to maintain the specific aver- 

 age. For here we have unlimited cell-multiplication 

 without any rejuvenescence by means of conjugation, 

 while the specific average is perfectly maintained by 

 the similarity of the conditions to which the different 

 individuals of the species are exposed. On the other 

 hand, Weismann's contention, that conjugation is not 

 necessarily essential to persistence, but is merely a con- 

 dition which is usually, but not always, advantageous — 

 so advantageous that in nearly all plants and animals it 

 periodically occurs — is fully borne out. 



Death, that is death from internal causes, from failure 

 of the vital powers, not death from external causes, such 

 as cold, hunger, accident, &c., occurs for quite another 

 reason, which may be set forth as follows. In those 

 plants which multiply by means of suckers or are 

 multiplied by means of cuttings, the cells whence the 

 individual is derived are to be regarded as little dif- 

 ferentiated and specialized, like the cells of the sponge, 

 cell-differentiation and specialization not having pro- 

 ceeded nearly so far among plants as among animals ; for 

 the highest plants are inferior in this respect to animals 

 low in the scale. As a result, while plants high in the 

 scale are able to reproduce otherwise than by means of 

 germ cells, animals comparatively very low in the scale 

 are not so able. They reproduce solely by means of 

 germ cells, for such, owing to specialization in function, 

 is the interdependence of their other cells, that these 

 latter cannot exist apart from one another, any more 

 than can a bricklayer, who does nothing else to support 

 life, exist apart from other men. They must remain part 

 of the organism or perish, while they cannot continue 

 to multiply iadefinitely, for then the organism would 

 grow too large for its available supply of nutriment. 



