APPENDIX III. DEATH OF PROTOZOA 



IN 1877 I pointed out that a Protozoon cannot be directly com- 

 * pared with a Metazdan {Proceedings Boston Society of Natural 

 History, April i8th, p. 170), and in 1879 formulated this opinion 

 more clearly. Since each Metazoon consists of many successive 

 generations of cells, it really is a cell cycle, and can only be 

 homologised with a cycle of protozoan generations, not with any 

 single Protozoon, which is but a single cell. Hence it follows 

 that the death of an individual Protozoon is not homologous with 

 the death of an individual multicellular animal. 



Weismann committed the fundamental error of assuming the 

 complete homology of the two forms of death, and thus reached 

 the false conclusion that Protozoa are all certainly potentially 

 immortal. The error is all the more important because without 

 assuming its truth the whole speculative structure of germ 

 plasm hypotheses cannot stand. As Oskar Hertwig has already 

 expounded in the first part of his Zeit und Streitfragen the de- 

 pendence of Weismann's " Keimplasm " doctrines upon the 

 incorrect hypothesis of Protozoon immortality, it is unnecessary 

 to discuss the matter further. 



Concerning Weismann's notions about death a few words may 

 be added. His view was first published in 1882, in his essay 

 Ueber die Dauer des Lebens, and it has been again advocated in 

 his article Ueber Leben und 7^^(1884), and has been defended 

 by him subsequently. 1 Weismann missed the real problem, which 

 is whether Protozoa like Metazoa develop in senescent cell cycles. 

 My position is unchanged, and is clearly presented by the 

 following quotation from an article in the American Naturalist : 



" He [Weismann] misses the real problem. The following 



1 E. g , Biologisches Centralblatt., iv., p. 690. 



262 



