PERIODIC REORGANIZATION IN PARAMAECIUM 457 



ent paper involves. It is important, however, at this point to 

 emphasize that the process herein described is not a phenomenon 

 pecuHar to the organisms of this culture after the 4020th gen- 

 eration, but that it was in progress throughout the life of the 

 race. For this purpose various specimens from earlier gener- 

 ations are presented in the plates. For example, figure 23 (pi. 

 2) represents an animal from the main culture on May 1, 1910, 

 at the 1755th generation with its nuclear apparatus in a char- 

 acteristic stage of the process, i.e., the formation of the macro- 

 nuclear anlagen. This should be compared with figure 20 (pi. 2) 

 which shows an animal which is a descendant of the former after 

 a lapse of 2329 generations, i.e., it is in the 4084th generation. 

 The similarity of nuclear conditions also is evident in figures 

 21 and 22. Cases such as this could be multiplied but for 

 brevity it will suffice to note that among the preserved material 

 there are specimens in the 426, 910, 1201, 1452, 1498, etc., 

 generations which exhibit reorganization stages in all respects 

 the same as those the animals have shown during the past six 

 months of study. Consequently, when convenient, these have 

 been figured to illustrate the process. 



IV. CYTOLOGICAL DETAILS OF SERIES OF PEDIGREED CELLS IN 

 THE REORGANIZATION PROCESS FROM SUBCULTURE IE 



In the preceding description of the cytological changes in the 

 process the data from all lines were presented together in order 

 to afford a composite picture of the nuclear phenomena as they 

 appeared from tlie entire culture. It is the purpose of the pres- 

 ent section to resolve this picture into its component parts in 

 order to emphasize the exact sequence of events as actually 

 observed in individual pedigreed series of animals from single 

 lines and thus to demonstrate that our description of the process 

 is not derived merely by combining isolated stages found at 

 different times in the different lines, but by combining the data 

 from a large number of series of animals whose genetic relation 

 with each other was exactly known — each series showing a con- 

 siderable part of the process. In combining these series there 



THE JOUBNAL OF BXPEEIMBNTAL ZOOLOGY, VOL. 17, NO. 4 



