PERIODIC REORGANIZATION IN PARAMAECIUM 449 



Figure 40 (pi. 4) shows an actual cell to illustrate these state- 

 ments. The animal has many chromatin bodies and two micro- 

 nuclei which have just divided. Only because the fate of the cell 

 (Vlh, 4355th generation) is known, is it certain that these two 

 micronuclei are the two micronuclei which, by another micro- 

 nuclear division, form four micronuclei, two of which become 

 macronuclear anlagen. If the cytology of the cells related to 

 this cell were not known, its two micronuclei could be interpreted 

 as the products of the discussed third division, which, if it occurs, 

 should take place before the cell division in the climax. We have 

 in our pedigreed lines no indication of its occurrence. 



Only on the assumption that this important division in the 

 climax has different morphological structures from the other 

 divisions of the reorganization process would it be possible to 

 recognize it. However since we have only seen small elongated 

 spindles during the ascending phase there is no reliable morpho- 

 logical criterion to determine the presence of the third micro- 

 nuclear division. One might expect that the condition of the 

 chromatin bodies would give some indication of the extent to 

 which the process has advanced and therefore of the number of 

 micronuclear divisions which has occurred. But this is not a 

 positive criterion because the disintegration of the chromatin 

 bodies does not progress with equal rapidity in all cells. 



We are certain, from the combined evidence from our cytolog- 

 ical study and from physiological data which will be presented 

 later, that the micronuclear division which would be comparable 

 to that which forms the stationary and migratory micronuclei 

 in conjugating animals is absent in the reorganization process. 

 In conjugation the reorganization of the nuclear apparatus is 

 consummated by the syncaryon. In the reorganization process 

 the so-called reduction micronuclei or their descendants give 

 rise to the new nuclear apparatus. This significant feature is 

 obviously of great importance from the standpoint of the theo- 

 retical interpretation of the reorganization process which we 

 describe. 



A brief survey of all the stages from the climax which we have 

 figured in the plates substantiate, we believe, the cytological 



