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THE AMERICAN NATURALIST [Yol. XLIX 



the interpretation given them, seemed to contradict 

 Weisinann's conception. Thus Maupas found that vari- 

 ous kinds of infusoria did not propagate by fission indefi- 

 nitely, but that a sexual process, conjugation, was neces- 

 sary at certain times, and Calkins showed that there were 

 regular periods of depression, and while a spontaneous 

 recuperation from the effects of certain depressions could 

 take place and in still other cases artificial stimulation 

 would aid the animals in overcoming the critical periods, 

 at other times depressions proved fatal without an inter- 

 vening conjugation. Woodruff, however, by choosing 

 conditions of environment more in accordance with the 

 conditions found in nature, could keep a strain of Par- 

 amecium apparently indefinitely alive without any inter- 

 vening periods of copulation being required. This seemed 

 to point to a potential immortality of protozoa in the 

 sense of Weismann. Recently, however, Woodruff and 

 Erdmann 7 found that the recovery from depression which 

 takes place is accomplished through nuclear changes com- 

 parable to, but not identical with, those observed during 

 copulation. This seems in some respects to agree with 

 R. Hertwig's previously enunciated theory according to 

 which depressions and senility in cells are due to a dis- 

 proportion between the nuclear and cytoplasmic material, 

 and that recovery from such unfavorable conditions de- 

 pends upon the reorganization of the nucleus, essentially 

 consisting in a diminution of the mass of the latter. Inas- 

 much as in metazoa — he concluded, further — such a rear- 

 rangement between nuclear and cytoplasmic masses can 

 only take place in the case of germ cells, but not somatic 

 cells, only germ cells are immortal, while somatic cells 

 are necessarily mortal. While Weismann regarded the 

 unavoidable mortality of the somatic cells as a secondary 

 acquisition, the result of a process of selection, the death 

 of somatic cells being of advantage to the propagation of 

 the race, Richard Hertwig 8 regards the death of somatic 

 cells as inherent in their structure, which precludes the 



7 Biol. Centralblatt, Bd. 34, August, 1914, p. 484. 

 sBiol. Centralblatt, B,l. XXXIV. 1914, No. 9. 



