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THE AMERICAN NATURALIST [Vol. XLIX 



aurelia possess the potentiality to perpetuate themselves 

 indefinitely by division under proper environmental con- 

 ditions. In short, his results have given almost the only 

 experimental evidence in support of the view, advocated 

 by Weismann, that protozoa are potentially immortal. 



The importance of this generalization and the deduc- 

 tions from it are self evident, and it is unfortunate that 

 so many should have advanced it before the life history 

 of Paramecium aurelia was fully known. Woodruff is to 

 be congratulated, however, in that he, with Miss Erdmann, 

 has now worked out stages in the life history of this or- 

 ganism which go far in clearing up the discrepancy be- 

 tween his results and those obtained by Maupas and his 

 followers. 



Woodruff has carried on his pedigreed race of Para- 

 mecium aurelia for more than seven years with a fairly 

 uniform division rate, subject, however, to occasional and 

 periodic fluctuations which he calls rhythms. These cor- 

 respond roughly to what I have termed cycles which end 

 in depression periods and, unless stimulated, by death; 

 in rhythms, however, Woodruff maintains, there is no evi- 

 dence of depression. 3 Recently Woodruff finds from a care- 

 ful study of material fixed during the low periods of his 

 division rate rhythms that there takes place a complete 

 nuclear reorganization, after which the organisms continue 

 to live with renewed vitality as shown by the ascending 

 division rate. This process consists in the disintegration 

 and probable absorption in the cytoplasm of the old macro- 

 nucleus, one or more divisions each of the old micronuclei, 

 degeneration of some of the products of these divisions, 

 and the ultimate reformation of functional macronuclei 

 and micronuclei from others. These are, in essence, the 

 important new facts which cytological study has revealed 

 in the life history of Paramecium aurelia, and some evi- 



8 1 would like to suggest to Professor Woodruff that he work out the 



I venture to predict he will find that the death rate rises with the decline of 

 the division rate and during the low sweep of the rhythms. 



