PERIODIC REORGANIZATION IN PARAMAECIUM 473 



V. THE REORGANIZATION PROCESS IN THIS RACE AFTER 



CONJUGATION AND IN OTHER RACES AND 



SPECIES OF PARAMAECIUM 



So far it is clear that the nuclear reorganization occurred 

 throughout the life of this race bred under conditions which 

 absolutely precluded the occurrence of conjugation, and the ques- 

 tion arises here : Would the process again occur periodically after 

 conjugation had taken place? Animals were accordingly isolated 

 from this race at the 4102d generation and with them a large 

 mass culture was started in a stender dish. Within a few days a 

 number of conjugating pairs were observed and about twenty were 

 isolated. Some of the animals were preserved for details of con- 

 jugation in this race, while the descendants of other ex-conjugants 

 were bred on depression slides by the same isolation culture 

 methods as those used in the main culture from which they were 

 derived at the 4102d generation. A study of the animals pre- 

 served from these ex-conjugant lines demonstrates that the same 

 reorganization process was resuined in all the lines within a rela- 

 tively short time after conjugation. 



More positive evidence could hardly be presented to prove 

 that the process is a fundamental normal periodic phenomenon 

 in the life of this race of Paramaecium aurelia. 



This being established, the question arises: Is this a peculi- 

 arity of this race or does the process occur generally in Paramae- 

 cium aurelia? This we can also answer conclusively. Erdmann 

 on August 11, 1912, isolated a specimen of Paramaecium aurelia 

 from a canal of the river Spree in Berlin and bred its descendants 

 by the daily isolation method on a culture medium of beef ex- 

 tract. Specimens from Erdmann 's race, bred by this method 

 which absolutely prevents conjugation, were preserved from time 

 to time and figure 24 (pi. 2) shows one of these in a characteristic 

 stage of the process under discussion, i.e., the formation of the 

 macronuclear anlagen. Thus it is evident that the same nuclear 

 reorganization which has occurred throughout the life of Wood- 

 ruff's race started with a specimen of Paramaecium aurelia iso- 

 lated at random in America in 1907 also occurred inErdmann's 

 race similarly isolated in Germany in 1912. 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 17, NO. 4 



