PERIODIC REORGANIZATION OF P. CAUDATUM 75 



This is in harmony with the stages in the reorganization process 

 in our races having four anlageii and two micronuclei (figs. 20 

 and 21) which follow without a cell division the stage with four 

 macronuclear anlagen and four micronuclei (fig. 19). 



The reconstruction in the reorganization process of the typical 

 vegetative Paramaecium cell is now effected by two cells divisions. 

 Figure 22 shows an animal which has undergone both of these 

 divisions. The cell has a single well developed anlage which 

 has attained more typical macronuclear characteristics. The 

 chromatin bodies are rapidly degenerating. The reorganized 

 cell at the very beginning of the new rhythmical period is shown 

 in figure 23. 



A critical survey of the ascending phase shows that even in 

 our small tube cultures, which might be compared with Kasan- 

 zeff's culture methods (except that he starved his animals while 

 we attempted to supply ideal conditions), relatively few Para- 

 maecium caudatum were able to accomplish the reorganization 

 process. This is in agreement with Popoff's results because he 

 found, according to our interpretation, only the early stages 

 of the reorganization process. Calkins, though studying care- 

 fully his pedigreed cells, figures but one animal which we would 

 interpret as showing the completion of the reorganization proc- 

 ess ('14, III, text figs. 19 and 20), Hertwig has never observed 

 what he considered a reorganization process in Paramaecium 

 caudatum ('14, pp. 568, 569). We ourselves, using the same 

 methods which proved successful in Paramaecium aurelia and 

 also new ones adapted to the peculiarities of Paramaecium cau- 

 datum in culture, could not work out in such detail the uninter- 

 rupted sequence of endomictic events from pedigreed series of 

 cells as in the case of Paramaecium aurelia. Nevertheless we 

 have proved that the process of reorganization can be success- 

 fully accomplished in certain cases under pedigreed slide con- 

 ditions though it is clear that these artificial slide cultures afford 

 obstacles which the average caudatum cell finds it difficult to 

 overcome when in the critical climax of the reorganization proc- 

 ess or of conjugation. We believe the data presented establish 

 beyond doubt that the reorganization process is a normal periodic 

 event in the life history of Paramaecium caudatum. 



THE JOUBNAL OF EXPERIMENTAL ZOOLOGY, VOL. 20, NO. 2 



