APPENDIX III 265 



If it be admitted that the mark of senescence in the Metazoa is 

 increase in the proportion of protoplasm, and the mark of reju- 

 venation increase of the nuclei, then we must expect similar 

 variations in the protozoa, if there be true senescence and re- 

 juvenation among them. It is probable that the observations to 

 decide this question can be made without serious difficulty, 

 and indeed I think they will soon be successfully accomplished. 



Professor Richard Hertwig has also developed views concern- 

 ing the death of Protozoa, which are certainly interesting, sug- 

 gestive, and important and have been summarised by the author 

 in a special article. 1 He accepts the views of Calkins as to 

 "depression" among Protozoa, but thinks that a further explanation 

 is necessary to explain senescence among Metazoa. I quote 

 from p. 23 of reprint : " Die Teilungsfahigkeit der Zellen eines 

 ausgewachsenen Menschen oder Tieres ist also nicht erloschen, 

 sie ist nur nicht im Stande sich zu betatigen ; sie ist zuriick- 

 gehalten. . . . Mit anderen worten die Zellen eines hoch- 

 entwickelten Tieres teilen sich nicht, weil sie den Wachsthums- 

 gesetzen des Ganzen unterworfen sind, wie ein jeder von uns den 

 Gesetzen des Staates." I agree with Professor Hertwig that the 

 inhibition of growth plays an extremely important role in the 

 higher animals, but as this whole volume argues, I think that 

 cytomorphosis produces true senescence of individual cells, and 

 that this senescence is more fundamental and essential than the 

 inhibitory control. 



The paper by M. Hartmann" on Death, I have not seen. 

 From a review of it in the Zoologisches Centralblatt., 1907, 543, I 

 infer that he has revived the idea that reproduction is the cause 

 of death. He is said to maintain that natural death does occur 

 among the protozoa. The review cited says: "Das Resultat seiner 

 Erorterungun fasst unser Autor dahin zusammen dass alien Pro- 

 tozoen (Protisten ueberhaupt)'ein natlirlicher Tod zukommt und 

 dieser ausnahmslos mit der Fortpflanzung zusammenfallt." 



1 R. Hertwig, "Uber die Ursache des Todes," Beilage zur Allgemeinen Zri~ 

 tung, Dez. 12 u. 13, 1906. 



2 M. Hartmann, Tod und Fortpflanzung, Mlinchen, 1906. 



