AUTHOR’S ABSTRACT OF THIS PAPER ISSUED 
BY THE BIBLIOGRAPHIC SERVICE, JULY 26 
UROLEPTUS MOBILIS ENGELM. 
Ill. A STUDY IN VITALITY 
GARY N. CALKINS 
ONE CHART AND TWO DIAGRAMS 
In the second of these studies (Calkins, ’19, Uroleptus mobilis. 
II. Renewal of Vitality through Conjugation, Jour. Exper. Zodl., 
vol. 29, no. 2) it was demonstrated that the protoplasm repre- 
sented by a single individual ex-conjugant undergoes a progressive 
decrease in vitality with continued age and division, and ulti- 
mately dies from what Maupas without hesitation designated 
old age. It was also shown that individuals derived from this 
protoplasm, if allowed to conjugate at any time during the life- 
cycle of the series, will regain their lost vitality and repeat the 
cycle. Up to the present time nineteen different series have 
thus completed full life-cycles and have died from exhausted 
vitality, while fourteen other series, descendants of the same 
protoplasm, are now under culture. Seventeen of these ex- 
hausted series started as ex-conjugants and two from cysts. 
Environmental conditions have been maintained as nearly con- 
stant as possible and the same standardized culture medium has 
been used throughout. The daily records for each series have 
been averaged for ten-day periods, and the latter averaged for 
sixty-day periods, thus giving a basis for comparison of vitality 
at different periods of the same cycle. 
During the ordinary routine of recording and transferring from 
day to day it was quite apparent that differences in vitality be- - 
tween different series were characteristic. Some series were 
strong and vigorous, while others were decidedly weak; such 
differences, however, are not always indicated by the division 
rates or by the curves based upon them, and the records must 
be further analyzed to bring them out. In some cases, on the 
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THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 31, No. 2 
