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



lected have the greatest importance on the extent of \dtality in 

 organisms under culture. This was hinted by Simpson (p. 410, 

 '01) when he spoke of the 'individuality' of different Pa'ramecia, 

 and by Woodruff ('05) ''My cultures lead me to believe with 

 Simpson, that the personal equation, if I may use that term, of 

 the individual selected to start a culture, has the most influence 

 in determining the number of generations attained before the 

 'initial potential of vitality' is exhausted" (p. 604) and again by 

 Gregory ('09) "Each individual of the same species as well as 

 of different species, has its own peculiar protoplasm reactions" 

 (p. 414). Finally, Woodruff ('09) re-states the point as follows: 

 "Again, it is possible that the different races of Paramecium 

 which Jennings has been able to isolate may have a physiological 

 as well as a morphological basis of distinction" (p. 303). 



It is on the basis of these individual differences that an ex- 

 planation is to be sought of the long-continued vitality of Wood- 

 ruff's cultures. The results of our present investigation show 

 convincingly that a single ex-conjugant gives rise to varied progeny 

 in the form of pure lines, each line remaining true to its type for 

 many months at least. Some of these are conjugating lines (all 

 the progeny of one quadrant in the J series) , while others are non- 

 conjugating or weak-conjugating lines. The old tradition, clearly 

 formulated by Weismann, that every protozoan is a potential 

 geim cell, must therefore be modified. Now, Woodruff's P. au- 

 relia is a non-conjugating pure line. He has repeatedly tried to 

 induce conjugation, using every device that has proved success- 

 ful in other cases, but to no avail. "Up to the present time, 

 however, there has been no tendency to conjugate among the 

 Paramecia of this culture and a large series of experiments, which 

 have been made with the individuals left over from the four lines 

 of the culture after the daily isolations have, so far, yielded not 

 a single pair of conjugants" ('11, p. 264). Jenning's cultures of 

 P. aurelia on the other hand conjugate regularly: "It is thus 

 clear that the race k (aurelia) has a remarkable tendency to con- 

 jugate readily, even though the progeny of only one individual 

 are involved ('10, p. 285). 



