PERIODIC REORGANIZATION IN PARAMAECIUM 483 



tune use of artificial stimuli. At the last cycle when all the 

 methods of rejuvenation which were tried proved of no avail 

 Calkins observed that the signs of degeneration were apparent 

 in the micronuclei and, therefore, concluded that at last 'ger- 

 minal death' occurred. 



Some very suggestive nuclear conditions are figured by Calkins 

 ('04) from animals in his depression periods. Calkins' figure 15, 

 plate 2, shows an animal of his B series just before its death in 

 the 502d generation, which had been treated with beef extract. 

 He states ''that the micronucleus has divided three or more 

 times and the daughter nuclei have accumulated at one end." 

 His photograph does not convince us that these are really micro- 

 nuclei. If they are they clearly represent an early "reduction" 

 phase of the process as described by us for Paramaecium aurelia. 

 We are inclined, however, to interpret these 'micronuclei' as 

 chromatin bodies since we have found that in Paramaecium 

 caudatum, as in Paramaecium aurelia, this is the method of 

 dissolution of the macronucleus during the process. This figure 

 of Calkins should be compared with our figure 34 (pi. 3) which 

 shows the chromatin bodies in Paramaecium caudatuvi. Text 

 figure 19 (Calkins' fig. 16, pi. 2) shows an animal from his 



A series in the 602nd generation treated for twenty-five minutes 

 with phosphoric acid. It was transferred to hay infusion and killed 

 twenty-four hours afterwards. The macronucleus is broken into frag- 

 ments; the micronucleus has divided and one part (left center) seems 

 to be forming a new macronucleus. (This individual offers the only 

 evidence obtained of nuclear fragmentation and reconstruction through 

 artificial means.) 



This suggestive comment by Calkins, given merely in his 

 description of plates, apparently hits the mark. We must inter- 

 pret this depression animal of Calkins, which he attempted to 

 'rejuvenate' by phosphoric acid, as at the end of the climax of 

 our process with many chromatin bodies and two macronuclear 

 anlagen. The micronuclear condition is not clear from the photo- 

 graph (compare text figs. 19 and 20, p. 484). 



Maupas' observation that in certain hypotrichous forms the 

 micronuclei in some periods may be increased to a number 



