PERIODIC REORGANIZATION IN PARAMAECIUM 495 



1. Paramaecium aurelia can reproduce indefinitely without 

 conjugation under favorable environmental conditions. The so- 

 called life cycle is non-existent. 



2. Minoj periodic fluctuations (rhythms) occur in the rate of 

 reproduction. 



3. The rhythms are the obvious physiological expression of 

 periodic internal phenomena. 



4. The internal nuclear phenomena comprise the formation 

 of a complete new nuclear apparatus of micronuclear origin. 

 This process we term 'endomixis.' 



5. The essential cytological difference between endomixis and 

 conjugation is the absence of the third division which in conju- 

 gation forms the stationary and migratory micronuclei, and of 

 necessity the non-formation of a syncaryon. 



Now it is important to emphasize again that this race of 

 Paramaecium aurelia has existed (so far) for over seven years 

 and through more than 4500 generations in a perfectly normal 

 manner without conjugation, during which time it has undergone 

 endomixis frequently, undoubtedly on the average once each 

 month. Further, conjugation has been successfully consummated 

 by animals from this culture and therefore both endomixis and 

 conjugation are normal phenomena in the life of this same race. 



It seems clear then that this culture offers strong physiological 

 evidence against the interpretation of either of the first two 

 so-called reducing micronuclear divisions as actually being a 

 chromosome reducing division. Since the nuclear changes in en- 

 domixis and conjugation are fundamentally the same except for 

 the absence of the third micronuclear division in the former, it 

 is justifiable to regard this third micronuclear division which 

 occurs in conjugation as the one directly preparatory, from the 

 standpoint of chromosome reduction and sexual phenomena, for 

 the imminent accession of foreign chromatin in the form of the 

 migratory micronucleus of the other conjugant. 



Endomixis, involving as it does the disintegration and absorp^ 

 tion of the old macronuclear and micronuclear material, affords 

 the opportunity for molecular rearrangement and therefore may 

 afford the opportunity for the origin of variations within a pure 





