PHYSIOLOGICAL VARIATIONS IN PARAMECIUM 523 



by the division rate (diagram 1), and (b) a greater stability in 

 regard to size as shown by the measurements at different periods 

 (diagram 2). 



6. Records of the conjugation tests show that the maximum con- 

 jugating power of fertile lines is attained from the fifth to the 

 seventh day after seeding the rich cultures and after the second 

 day after transferring from the rich cultures to Syracuse dishes. 



7. These differences in physiological activities of pure lines 

 of Paramecium point to the explanation of the diverse results 

 and conclusions obtained by different observers with Parame- 

 cium in culture. Many pure Unes die out from a 'natural death;' 

 others, notably the conjugating hues, are relatively weak; still 

 others have a high potential of vitaUty. Woodruff's Parame- 

 cium aurelia is evidently a Paramecium Methuselah belonging to 

 a non-conjugating line the life history of which is not known in 

 any case. 



8. The statement that every protozoon is a potential germ 

 cell is not true. The power to conjugate is not possessed by every 

 Paramecium and up to the present it has not been proved that 

 the progeny from every Paramecium will develop the power to 

 conjugate. The evidence from Woodruff's culture, and from our 

 J series, indicates that some Unes apparently lack even the po- 

 tental'of conjugating power, but this is a matter which continued 

 observation alone will decide. 



9. The results of this study show that physiological and mor- 

 phological variations in the progeny of a single ex-con jugant of 

 Paramecium caudatum are fully as extensive as the variations 

 between progenies from different ex-conjugants. The arguments 

 based upon the latter variations to the effect that conjugation 

 is for the purpose of originating ^-ariations cannot therefore be 

 sustained. 



Experiments here re-described show that the vitality of a given 

 race is increased by conjugation. An ex-conjugant from a pure 

 line that had lived for 369 generations in culture, divided 376 

 times after conjugation in nine months, while the pure line con- 

 trol that had not conjugated, and from which the ex-conjugant 

 was obtained, divided only 277 times in the same period. Fur- 



