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GARY N. CALKINS 



vitality and a progressively waning vigor leading to death, 

 while other series, obtained from these by conjugation, fed at the 

 same times on the same standardized culture medium, are now liv- 

 ing actively. Counting from the day on which the first division 

 of the ex-con jugant occurred to the day on which the last division 

 occurred, the protoplasm of the A series divided during 267 days; 

 that of the C series during 294 days; the D series, 215 days; the 

 F series, 256 days; the G series, 253 days, and the H series, 245 

 days. The total number of divisions and the average division 

 rate per individual in each series are shown in table 3. 



The C series had the greatest vitality in regard to endurance, 

 while the F series had the greatest vitality in regard to division 



energy. In the latter case the individuals in each line divided 

 on the average 12.38 times in ten days, while in the C series the 

 average was 11.87, and in the H series it fell to 10.93. The dif- 

 ference between F and C is too slight for comment, but that 

 between F and H or between D and H may have some signifi- 

 cance in connection with the problem as to whether the offspring 

 vary in vitality according to the age of the parents at the time 

 of conjugation. I have not enough data at present to throw 

 much light on this problem, but the data from which table 3 

 was derived may be further analyzed to show how the differences 

 between the different series are distributed in the life cycles. 



It is shown above that the first conjugations in a series occur, 

 as a rule, from fifty to seventy days after the first division of the 

 ex-conjugant which gives rise to the series. Sixty days, therefore, 

 may be chosen as approximately the period elapsing before the 

 first conjugation in a series, and a period representing the stage 



