66 RHODA ERDMANN AND LORANDE L. WOODRUFF 



only at one point when the cytoplasm itself has nearly completed 

 division('14, III, fig. 7). 



To summarize: The loss of chromatin occurs either by the 

 extrusion of chromatin bodies (Paramaecium caudatum and 

 Paramaecium aurelia) ; by extrusion of small granules from the 

 macronucleus (Paramaecium caudatum) ; by breaking up of the 

 old macronucleus into two or more large pieces (Paramaecium 

 caudatum; Paramaecium aurelia, Hertwig '89, p. 74). The 

 result — the total destruction of the individuality of the macro- 

 nucleus — is the same in each case. 



Extruded chromatin bodies were figured by Calkins '04 (fig. 

 16) in Paramaecium caudatum and these we have compared with 

 certain stages of Paramaecium aurelia at the beginning of the 

 ascending phase of the process of reorganization ('14, III, p. 484, 

 text figs. 20 from our own preparations, and 19, copied from 

 Calkins). Calkins does not mention how the nuclear fragmen- 

 tation has been effected but this probably has occurred in the 

 same way as we have described in our cultures of Paramaecium 

 aurelia (Woodruff's main culture I, and Erdmann's culture B) 

 and in some animals from our culture Y of Paramaecium cauda- 

 tum ('14, III, fig. 34), because the morphological features are 

 identical. Those cultures of Paramaecium caudatum, in which 

 the macronucleus breaks into large pieces, present in the further 

 stages of macronuclear degeneration a different cytological 

 appearance as is shown in an animal from about the 82d gene- 

 ration, culture Y (fig. 8). Here the chromatin is distributed 

 in the cell without first being condensed into spherical chromatin 

 bodies. The macronuclear membrane is torn and its contents 

 are intermingling with the cytoplasm. This general type of 

 fragmentation of the macronucleus has been described with 

 different interpretations by several authors, for example, Kasan- 

 zeff '01, working under R. Hertwig; Popoff '07, figure 18, plate 4; 

 Popoff '09, figure 26, plat-^ 2 ; Calkins '04, figure 8, plate 1 and figure 

 11, right animal, plate 2; and Hertwig '14, p. 568. All these 

 authors considered these changes as depression phenomena which, 

 according to Popoff, have close resemblance to phenomena 

 characteristic of the onset of conjugation. 



