REJUVENESCENCE IN UROLEPTUS MOBILIS 137 



of immaturity of the protoplasm. Adopting sixty days as a 

 unit period, it is possible to work out from the daily records the 

 division rates in all series for the first, second, third, and fourth 

 sixty days of each series to date. These are shown in table 4 

 in which the mean division rate of a series per day and its prob- 

 able error have been worked out by Davenport's formulae as 

 shortened by Oampton. For comparison with the preceding 

 tables, these rates are divided by five and multiplied by ten 

 (multiplied by two) to give the number of divisions which each 

 of the five lines of protoplasm of a series is capable of undergoing 

 in ten days. The G series is omitted from this table, as it rep- 

 resented protoplasm which did not come from the original A 

 series. Three other series, I, J, and L, are introduced, although 

 only one period of the last is involved. The mean for the first 

 sixty days of the A series is not included, since this represents 

 the period of experimentation with the culture media at the 

 outset of the work; the standard culture media was first used 

 with this series ten days before the beginning of the second 

 sixty-day period. 



The remarkable uniformity of the division rates during the 

 first sixty days in all series regardless of the source, or calendar 

 period, or age of parent, indicates that every ex-conjugant com- 

 posed of a portion of the original protoplasm derived from A begins 

 its life cycle with a definite optimum division energy indicated by 

 17.1 to 17.9 divisions per line in ten days. This is the average rate 

 for sixty days, and the rate for the first or second ten day period 

 may be lower or higher than the average for sixty days. Refer- 

 ring to table 2, we find a higher rate than the mean for sixty days 

 in the first ten-day periods of series C, H, and I; while it is lower 

 than the mean for the first sixty days, in the first ten-day periods 

 of series D, F, J, and L. These averages for the first ten days 

 may be even less than the averages for the same calendar periods 

 of the parental series, a fact which furnishes the kind of evidence 

 that has been used by some experimenters as an argument against 

 rejuvenescence by conjugation. Thus in the first ten-day period 

 of the C series, the division rate was 18.6 while that of the parental 

 A series in the same period was 20.8. Again the F series, with 



