PERIODIC REORGANIZATION IN PARAMAECIUM 445 



The posterior animal still contains a piece of the old macronuclear 

 membrane. It is possible that the two micronuclei in this divid- 

 ing animal (fig. 15, pi. 2) are the result of a division of a single 

 'reduction' micronucleus which alone remained in the parent cell. 

 It is also possible that both of these micronuclei are the 'reduction' 

 micronuclei which did not degenerate and which are now, after 

 a long period of passivity, distributed to each of the daughter 

 cells. In this case the formation of a new spindle could not have 

 occurred and the absence of the micronuclear division would be 

 proof that the process is effected in this way. In eight cases of 

 the process the cytological study has shown that a cell division 

 actually does occur. Such cases fall under the heading la and 

 lb in text figure 3. 



The discussion of the micronuclear events preceding the cell 

 division in the climax will be postponed until all the cytological 

 data from the study of the climax have been presented. 



The morphology of the cell after the cell division in the climax 

 was definitely determined from several specimens (see fig. 15, 

 pi. 2, and figs. 41 and 40, pi. 4). Clearly the reorganization of 

 the nuclear apparatus is effected by a single micronucleus in all 

 cases in which a cell division occurs in the climax. Figures 41 

 and 42 (pi. 4) give two cells in the 4436th and 4437th generations 

 respectively. Cell 4436 has one micronucleus and numerous 

 chromatin bodies and is an animal after the cell- division in the 

 climax. Cell 4437, which is a product of the first division of the 

 sister cell of cell 4436 after about forty-eight hours, already has 

 one macronuclear anlage. This proves that, after the discussed 

 cell division in the climax, the one micronucleus forms, by two 

 subsequent divisions, four micronuclei, two of which become 

 macronuclear anlagen which are distributed by the succeeding 

 cell division to each of the two daughter cells. 



In figure 16a (pi. 2) is given a more advanced stage of 

 one of the cells inmiediately after division. This anterior cell • 

 (a) has just emerged from the climax, as is evident from the fact 

 that the formation of the macronuclear anlagen is completed. 

 The sister cell (b) has not undergone the same changes and one 

 micronucleus and several chromatin bodies, of which only five 



