ENDOMIXIS IN PARAMAECIUM AURELIA 47 



The discussion of these results may best be postponed until 

 further evidence has been presented bearing on the second ques- 

 tion above stated, namely: Is endomixis an evidence of depression 

 or a means of rejuvenation of a depressed race? These two hy- 

 potheses are not necessarily alternate to each other. Endomixis 

 may be both an expression of, and a means of relief from a de- 

 pressed condition. The hypothesis of Hertwig, Popoff and 

 others, according to which nuclear reorganization in Paramae- 

 cium is a parthenogenetic process is based on the generally ac- 

 cepted interpretation of conjugation, with its accompanying 

 nuclear reorganization, as a rejuvenating process. Jennings 

 ('13) however, and more recently Mast ('16) have shown that in 

 Paramaecium and Didinium this interpretation is very doubtful, 

 while Woodruff's well known culture of Paramaecium aurelia 

 has shown that a race of Protozoa may live indefinitely without 

 this process Woodruff and Erdmann ('14, '16) however main- 

 tain that the longevity of their race is due to the constantly 

 recurring nuclear reorganization or endomixis, and suggest that 

 rejuvenation occurs in conjugation also by virtue of the similar 

 process taking place at that time. 



The evidence for this interpretation is the occurrence of low 

 points in the division rate coincident with the reorganization 

 process, following which the division is restored to its normal 

 rate. This evidence however is proof merely of a certain corre- 

 spondence between depression periods and endomixis, and is no 

 more indication of a rejuvenating than of a depressing effect of 

 the latter. 



In my own experiments described and plotted above, I have 

 found that accompanying endomixis there is almost invari- 

 ably a temporary slowing down in the division rate. An excep- 

 tion is however seen in line III, 6/13-6/15 (fig. Ill), where the 

 process is associated with a rising rather than a falling division 

 rate. This is also seen in the exception noted by Woodruff and 

 Erdmann to which I have already referred. 15 



I have further found several instances of temporary reduction 

 in the division rate unaccompanied by endomixis. Cases of 



16 See page 35. 



