PERIODIC REORGANIZATION IN PARAMAECIUM 487 



data secured by Popoff in his study of the Ufe history of Sty- 

 lonychia mytilus shows that ''if the curve of Stylonychia is 

 plotted from average records of five and ten-day periods, it will 

 be found to correspond to the curves for Paramaecium, Oxy- 

 tricha and Tillina, each showing the rhythmic periods of high 

 and low vitality." We reproduce here (text fig. 22) Gregory's 

 curve plotted from Popoff's data, with the depression periods 

 indicated. This curve is obviously strikingly similar to the ones 

 which we give in the present paper to show the relation between 

 the process and the rhythms. It is to be noted that at the low 

 points between Popoff's 'rhythms,' just as at the low points 

 between our rhythms, nuclear changes occurred. This agree- 

 ment, taken in conjunction with the fact that Popoff's animals 

 show evidence of the process we describe, probably makes it 

 now safe to state that Popoff's small depression periods are 

 rhythms. Such being the case, we are in a position to identify 

 with more certainty the minor depressiori periods of Hertwig and 

 Calkins as rhythms also. 



When one considers the diverse culture methods used by the 

 various authors and that merely cells selected at relatively long 

 intervals and practically at random were studied by them, it 

 is remarkable that so many indications of the process may be 

 gleaned from their data. This affords additional evidence of 

 the general occurrence of this phenomenon in Infusoria. We 

 do not desire, however, to deny that abnoniial cytoplasmic and 

 nuclear conditions can and do occur in infusorian cultures, or 

 to seem to attempt to interpret as stages of the process all the 

 so-called degeneration stages figured by various authors. Now 

 and then an animal in the culture of Paramaecium under con- 

 sideration has failed to divide for several days and has finally 

 died without signs of the process. A study of such animals has 

 shown what ate certainly abnormal conditions of cytoplasm and 

 nucleus. The cytoplasm appears "diluted" and vacuolated, the 

 pellicle has a characteristic glistening effect, and the cell-contents 

 show more acidity than normal. The nucleus may assume vari- 

 ous atypical forms. Such a condition may arise in various ways, 

 but the usual one is the contamination of the medium with a 



