PERIODIC REORGANIZATION OF P. CAUDATUM 79 



Thus endomixis has now been demonstrated in each of the four 

 races which we have studied. 



Further, the idea of Hertwig that endomixis occurs only after 

 long cultivation of a race of Paramaecium was shown not to be 

 true in Woodruff's main culture. We stated ('14, II, p. 492) 

 that animals preserved during the first year of its cultivation 

 showed stages of the process, and further we stated that the race 

 from Berlin showed stages of endomixis very early in its history 

 ('14, II, p. 493). Now, with this point in mind, we have found 

 endomixis in each of the new aurelia races within the first thirty 

 days of their life in culture. 



Therefore, we have proved that endomixis is a phenomenon 

 common to all four races of Paramaecium aurelia which we have 

 studied and thus it is highly probable that it occurs in all races 

 of this species. Further, we have proved that endomixis is not 

 a phenomenon which is gradually acquired after long pedigreed 

 culture but is completely developed in animals at the time of 

 isolation from wild cultures, and still further we have proved 

 that endomixis is a potentiality of lines which have the power 

 of conjugation ('14, III, p. 473). 



Having, we believe, disposed of these questions which have 

 been raised in regard to our work on Paramaecium aurelia, we 

 are in a position to return to endomixis in Paramaecium cau- 

 datum. The cytological phenomena of this process have been 

 presented in the previous sections, and we believe that we estab- 

 lished beyond peradventure the truth of our statement ('14, III, 

 p. 475) that endomixis "occurs at least with essentially similar 

 features in Paramaecium caudatum also" and therefore that 

 endomixis is a regular normal periodic process in the life of 

 Paramaecium caudatum (text fig. 6). 



Early work on Woodruff's main culture of Paramaecium aurelia 

 ('09, '11) showed that there are periodic fluctuations (rhythms) 

 in the rate of reproduction which are not the results of environ- 

 mental variation, but which are due to some periodic internal 

 phenomena of unknown character (Woodruff and Baitsell, '11). 

 We have shown ('14) that endomixis is the underlying internal 

 process whose physiological effect had been observed but whose 



