70 



THE AMERICAN NATURALIST [Vol. XLIX 



ausseren Umstanden ohne Hilfe von Konj ligation oder einer kunstlichen 

 Reizung imstande ist, sich unbegrenzt fortzupflanzen und zeigt ferner in 

 klarer Weise, dass das Altern und das Befruchtungsbediirfnis nicht 

 Grundeigensehaften der lebendigen Substanz sind. 17 

 I am entirely in sympathy with Hertwig when he says, 

 in connection with this citation : 



Naeh meiner Ansieht sind die Resultate, zu denen in den unseren 

 Auseinandersetzungen zum Ausgangspunkt dienenden Artikel Wood- 

 ruff gemeinsam mit Rhoda Erdmann gelangt ist, mit den hier zitierten 

 Satzen unvereinbar. 18 



The discovery of parthenogenesis in the life cycle of 

 Paramecium aurelia by Woodruff and Erdmann clears up 

 the obscurity which has involved all theoretical discus- 

 sions following pedigreed culture work with infusoria, 

 and we now see with much clearer vision the probability, 

 first, that conjugation or its equivalent has primarily the 

 result, as originally interpreted by Biitschli, of offsetting 

 and overcoming the progressive weakening of vitality in 

 infusoria; second, that more or less definite cycles of 

 vigor and depression, ending in natural death unless con- 

 jugation or its equivalent supervenes, are characteristic 

 of all pedigreed races of infusoria; third, that physical 

 1 ' immortality" is true of Paramecium and other ciliates 

 only in the same sense that it is true of metazoa ; fourth 

 and last, that Paramecium protoplasm is subject to the 

 same laws of physiological usury that apply to metazoa, 

 and undergoes phenomena which, in metazoa, we call old 

 age, and which, as in metazoa, ends in natural death un- 

 less conjugation, or its equivalent parthenogenesis, saves 

 the race. 



