SPECIES NOT NECESSARILY CONDEMNED TO EXTINCTION 151 



tiation and evolution ; that it is an adaptation of the higher 

 multicellular organisms to the conditions of life itself, brought 

 about, as it is, by the necessity for the integral transmission of 

 an hereditary substance, and the impossibility of thus trans- 

 mitting a developed organism. Immortality — and this word 

 is to be understood in a merely biological sense — ^is the property 

 of the lowest organisms, and of the germ-plasm of the higher 

 organisms. The soma-plasm, however, is incapable of exceeding 

 certaiu age-limits. 



If we turn now from individual organisms to species, we do 

 not find any parallel between the ontogenetic development of 

 the one and the phylogenetic evolution of the other. This is 

 not to be understood as a denial of the biogenetic law, the 

 formulation of which by Fritz Miiller and Haeckel was one of 

 the most important events in the history of modern biology. 

 But though the embryonic development of the individual 

 recapitulates the history of the species, either in complete, 

 though abbreviated, fashion (palingenesis), or in a more or less 

 modified manner (cenogenesis), this does not imply that the 

 subsequent course of the ontogeny should resemble the phylogeny 

 of species in general. In other words, the phylogeny is not 

 necessarily subjected to the laws of birth, growth, decline, and 

 extinction, to which the ontogeny is subjected. 



Whereas the death of the soma is a constitutional necessity 

 for multiceUidar organisms, it does not appear that death is, 

 in the strict sense of the word, a necessity for the species. The 

 fact that the species is a complex of adaptations, that it has 

 its origiu in a variation which has been developed by natural 

 selection, shows that the species is not immortal or eternal ; 

 and palaeontology affords sufficient evidence of the fact that 

 ionumerable species have been annihilated in the course of 

 ages. Indeed, not only species, but entire genera — ^nay, entire 

 classes — ^have been rooted out ; and it has therefore been con- 

 cluded that every species must necessarily pass through the 



