68 EFFECTS OF ADAPTATION sec. 



Weismann replies, in his latest essay, such an arbitrary 

 definition of the term death is unjustifiable. The process of 

 encystment is by no means comparable with death, and does 

 not even occur in all I'rotozoa — a view which is certainly 

 correct. Weismann says further : " The gradual evolution 

 of death is to be explained in this way, that at the first differ- 

 entiation of the body of the JNIetazoon into somatic and germ- 

 cells, tlie life of all cells was limited to one generation, that of 

 the somatic, therefore, to a short duration. The somatic cells 

 first bej^an to last for several cjenerations amonoj the hidier 

 Metazoa, and life was prolonged. This change was brought 

 about by processes of selection, on the basis of the principle 

 of division of labour. The shorter or longer duration of life 

 depends entirely on adaptation. Death is not due to an 

 original property of living substance, nor is it necessarily con- 

 nected with reproduction. Eeproduction, on the other hand, 

 is an original property of living matter. Life is continuous, 

 not, as Gotte would have us believe, interrupted, discon- 

 tinuous." 



With rei]fard to the different views of Weismann and 

 Gotte, I have elsewhere ^ expressed myself as follows : " On 

 account of the definite evolution of science, certain ideas are 

 not far to seek. I have for years discussed the immortality 

 of the Protozoa in my lectures,^ but in consideration of the 

 action of metabolism, and the necessity of the renewal of 

 the organs of even these forms in consequence of wear, w^ould 

 place some limitations on its acceptance. 



" In the Metazoa, according to my opinion, the germ-cells 

 are immortal like the Protozoa (with the same limitations as 

 hold for the immortality of these) ; only the soma dies. 



" The latter is not really an end in itself,^ but rather its 



^ In a report in the Deutsche Literaturzeitunfj, 18S4, No. 19. 

 ^ Cf. also Blitschli, Zool. Anzeiger, 1882, p. 64. 



2 [It would be just as true to say that the germ-cells are not an end in them- 

 selves, but serve only to produce the soma. Trans.] 



