CONJUGATION OF PARAMAECIUM 239 



Eight depression slides were each filled with about five drops of 

 this culture of Paramaecium and placed in a moist chamber at 

 room temperature. The following morning (December 7, 1913) 

 a couple of conjugating pairs were discovered on each slide. At 

 this time material from the stender dish was again distributed on 

 depression slides and the next day again a couple of pairs were 

 isolated from several of these slides. About twenty pairs were 

 thus secured, some of which have been preserved at various 

 stages for cytological study and others as exconjugants initiated 

 lines which are now being bred by the same pedigreed culture 

 methods employed for the race from which they were originally 

 derived. Details of this work will be presented in a later paper. 



During the more than six and one-half years of the life of this 

 race a considerable amount of evidence has been accumulated 

 by different observers tending to show that the conditions de- 

 termining conjugation vary greatly in different races and in 

 different lines within the same race of Paramaecium aurelia and 

 Paramaecium caudatum. Jennings'* writes: ''Some races conju- 

 gate frequently, and under conditions readily supplied in experi- 

 mentation. Others, under the same conditions, conjugate very 

 rarely or not at all." Calkins^ finds that ''Some lines will con- 

 jugate whenever the conditions favorable for conjugation are pre- 

 pared; other lines have never conjugated under such conditions." 



These variations in the tendency to conjugate which are ex- 

 hibited by pure races and lines of Paramaecium apparently have 

 led Calkins to believe that "The traditional view that each Para- 

 maecium is a potential germ cell is not true,"^ and that herein 

 lies the clue to the directly opposite results derived from his 

 races and from mine:" 



* H. S. Jennings, Jour. Exp. Zool., vol. 9, 1910, p. 298. 



5 G. N. Calkins and L. H. Gregory, Jour. Exp. Zool., vol. 15, 1913, p. 509. 



« G. N. Calkins, Proc. Soc. for Exp. Biol, and Med,, vol. 10, 1913, p. 67. 



^Calkins (loc. cit.): "The life history of conjugating lines has shown that 

 if conjugation is prevented, the race dies out." Woodruff (loc. cit.): "I be- 

 lieve this culture shows clearly that Paramaecium aurelia when subjected to 

 suitable culture conditions, has the power of unlimited reproduction by division 

 without conjugation or artificial stimulation." 



