PERIODIC EEORGANIZATION OF P. CAFDATUM 



71 



went reorganization successfully in the 11th, 91st, 184th, 282d 

 and 398th generations, and Culture M at the 89th generation, 

 that is at intervals of about 90 generations, thus confirming our 

 observation on Culture Y that the reorganization process occurs 

 in Paramaecium caudatum at intervals of from 80 to 100 

 generations. 



The difficulty of securing stages of the climax and of the as- 

 cending phase compelled us, as previously stated, to amplify our 

 material of isolated pedigreed animals with small tube cultures 

 seeded from our pedigreed cultures, just before reorganization 

 was due to take place on the basis of our computation of the 



TABLE 3 

 Showing the occurrence of the reorganization process iji Culture Z 



number of generations since its last occurrence and by the divi- 

 sion rate. The most critical stage for the vitality of the race is 

 when the individuality of the macronucleus is lost and the chro- 

 matin bodies are undergoing degeneration. The results of 

 Calkins' extended experience with Paramaecium caudatum all 

 indicate that the culture of Paramaecium caudatum in isolated 

 lines on depression slides is sooner or later fatal. Woodruff's 

 comparison, ('lie, p. 60,) of pedigreed lines of Paramaecium 

 caudatum with those of his main culture of Paramaecium aurelia 

 showed clearly that it was impossible to breed indefinitely 

 Paramaecium caudatum by the daily isolation method which 

 was so highly favorable for Paramaecium aurelia. 



