SO-CALLED CONJUGATING AND NON-CONJUGATING 

 RACES OF PARAMAECIUM 



LORANDE LOSS WOODRUFF 

 Osborn Zoological Laboratory, Yale University 



ONE FIGURE 



An interesting characteristic of the pedigreed race of Para- 

 maecium aureHa,i which I have had under daily observation for 

 the past six years and eight months, has been the apparent abey- 

 ance of the tendency to conjugate during the first seventy-nine 

 months of its existence. Although the possibility of conjugation 

 has been prevented in the main lines of the race, a large series of 

 experiments have been made from time to time to induce conju- 

 gation in mass cultures started with individuals left over from the 

 daily isolations from the main lines. These experiments appar- 

 ently failed to afford just the proper environmental conditions 

 to initiate conjugation^ for not a single pair had been observed 

 before the experiment to be described below. 



On December 1, 1913, a large jarful of water and decaying 

 plants from an old laboratory amoeba culture was thoroughly 

 boiled for half-an-hour and a part of this material was then put 

 into a large, sterilized stender dish with ground-on cover, while 

 the rest was left in the container in which it was boiled. The 

 following day the contents of the stender dish was inoculated 

 with a considerable number of paramaecia left over from the 

 isolations that day (4102d generation). ^ At the end of five days 

 there was a heavy pure growth of paramaecia in the stender dish 

 but no protozoa of any kind in the uninoculated culture material. 



^ For details of the race, cf. L. L. Woodruff: Archiv fiir Protistenkunde, Bd. 

 21, 1911; Biochemical Bulletin, vol. 1, 1912. 



^ E.g., Baitsell (Jour. Exp. Zool., vol. 13, 1912, p. 73) from his experiments on 

 the life history of Stylonychia shows "that conjugation is induced by external 

 conditions affecting the organism." 



^ Cf. figure 1. 



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THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 2 



