PERIODIC REORGANIZATION OF P. CAUDATUM / / 



directly prove that the 'reduction' micronuclei in Paramaecium 

 aurelia in the reorganization process have somewhat different 

 morphological characteristics from those of the same species in 

 conjugation. 



The destruction of the macronucleus before the formation of 

 macronucleai' anlagen in Paramaecium aurelia occurs, according 

 to our observations, only by the extrusion of chromatin bodies 

 from the macronucleus. But in Paramaecium caudatum there 

 are clearly two methods of macronuclear dissolution in the de- 

 scending phase of the reorganization process. One of these 

 involves the breaking up of the macronucleus into one or more 

 large pieces which finally degenerate in the cell (figs. 8, 9 and 10) ; 

 the other involves the extrusion of chromatin bodies from the 

 more or less intact macronuclear membrane (figs. 14, 15 and 16). 

 This would seem to indicate that there may be also two distinct 

 methods of accomplishing the ascending phase of the reorganiza- 

 tion process in Paramaecium caudatum. One closely resembles 

 the process in Paramaecium aurelia, being characterized by 

 the presence of chromatin bodies, the absence of the old macro- 

 nucleus in a cell with one micronucleus, this single micronucleus 

 being the one which is to form the new nuclear apparatus. The 

 other method is characterized by the breaking of the macronu- 

 cleus into relatively large pieces and the streaming of chromatin 

 out into the cytoplasm (figs. 10 and 13). Thus when the macro- 

 nuclear destruction takes this form, there are few, if any, chro- 

 matin bodies to be found in the ascending phase. It may be 

 mentioned incidentally that we have some data which suggest 

 that under certain conditions merely a partial reorganization, 

 not involving the formation of macronuclear anlagen, may lead, 

 at least temporarily, to the continuance of the life of the line. 



Our material did not allow us to prove whether the third so- 

 called reduction division occurs or not, but we lean to the view, 

 on the basis of our detailed study of this point in Paramaecium 

 aurelia ('14, III, pp. 446-450 and p. 495) that this division actu- 

 ally is absent in the reorganization process in Paramaecium cauda- 

 tum as in Paramaecium aurelia. Further, we have no indication 



