504 G. N. CALKINS AND L. H. GREGORY 



ond and third. After eight days the same is true. After ten 

 or fourteen days conjugations appear chiefly after two or three 

 days subsequent to transference. We have seen (table 5) that 

 the period of maximum maturity is reached on the seventh day 

 of rich feeding, and from this present table the conclusion maj'- 

 be drawn that the response to the changed environment is more 

 rapid and more intense the nearer the period of maturity is ap- 

 proached. Or, the results may be summarized in another way 

 as follows: of 8464 pairs observed in the Syracuse dishes 540 

 appeared on the first day after transferring; 5109 pairs appeared 

 on the second day; 2270 on the third day; 545 on the fourth 

 day and none at all on the subsequent days. The maximum con- 

 jugation power therefore is found on the second day after trans- 

 ference to Syracuse dishes of Parameciuln which have been for 

 seven days in a rich culture. 



8. DISCUSSION 



These experiments demonstrated clearly that there are well 

 marked physiological variations in different 'pure lines' of Par- 

 amecium caudatum all derived from the same ancestral ex-con- 

 jugant, and in the light of 'these results it is necessary to re-open 

 some of the old questions in general biology. These questions 

 are: 



A. Is there a limited potential of vitality common to the fer- 

 tilized metazoan egg, and the ex-conjugant Paramecium? 



B. Are all protozoa potential germ cells? 



C. Do some protozoa die a natural death from old age? 



D. Are variations which arise through amphimixis different 

 from those which arise by differentiation of any ex-conjugant? 



E. Is rejuvenescence or is amphimixis the most important 

 effect of conjugation? 



A. The potential of vitality 



The experiments and observations of Maupas ('88), Joukowsky 

 ('98) and Simpson ('01) all indicated a limited metabolic activ- 

 ity for Paramecium and allied forms in cultures, the general 

 result being that the race dies after some three months under 

 these conditions. Calkins' experiments ('02-'04) were made with 



