PERIODIC REORGANIZATION OF P. CATTDATl'M 65 



Calkins and Cull do not describe a 'dumb-bell' formation in the 

 first reduction division in conjugation, but we must interpret our 

 figure as the first 'reduction' division of the reorganization proc- 

 ess because no trace of other micronuclei are in the cell. An 

 animal in the second 'reduction' division is shown in figure 10. 

 Two micronuclei are dividing. In one the equatorial band of 

 chromatin is intact while in the other it is divided. The macro- 

 nucleus, fragmentated into two parts, is rapidly losing its chro- 

 matin. 



The breaking up of the macroiiucleus begins relatively late in 

 Paramaecium caudatum and generally does not extend through 

 several generations as we found to occur in the descending phase 

 of the process in Paramaecium aurelia (Compare '14, III, pi, 1). 

 The expulsion of chromatin bodies (figs. 14, 15 and 1(3) or the 

 breaking of the macronucleus into two or more pieces (figs. 9, 

 10 and 11) seem to be a rapid process in the life of the caudatum 

 cell. Culture Z, 91st generation (fig. 13) does not show the 

 slightest trace of chromatin bodies, but in the 93d generation 

 (fig. 14) there are many of them in the cytoplasm. These chro- 

 matin bodies, however, do not have the definite condensed ap- 

 pearance so characteristic of those in Paramaecium aurelia, but 

 are relatively pale and indistinct and seem to suddenly appear 

 in nearly maximum numbers. This possibly may be accounted 

 for by the fact already mentioned that in Paramaecium caudatum 

 finely divided chromatin material, in certain cases at least, streams 

 from the macronucleus into the cytoplasm. This leaves a pau- 

 city of chromatin for the chromatin bodies and may change the 

 tension within the macronuclear membrane so that the chromatin 

 bodies are formed rapidly and thus appear suddenly. Figure 

 13 gives a good idea of this phenomenon, as does also figure 6 

 in which the macronucleus is partly devoid of chromatin while 

 no chromatin bodies are visible. 



This breaking up of the macronucleus into large pieces was 

 observed in animals from small tube cultures (fig. 10) as well as 

 in isolated animals (figs. 9 and 11) as already described. These 

 animals cannot be dividing specimens because in normal vege- 

 tative divisions the macronucleus is greatly elongated and breaks 



