KEJUVENESCENCE IN UROLEPTUS MOBILIS 129 



day period covers almost every stage of a typical life cycle. It 

 includes a late stage of the A series and the initial stage of the I 

 series, while the others are intermediate. 



The five different lines of a series thus give consistent records 

 in number of divisions in the same calendar period, so that an 

 average of all five lines gives a fairly accurate idea of the vitality 

 of the protoplasm of a series for that period. Table 2 is a list of 

 such averages for all series in the same consecutive calendar 

 ten-day periods. 



The averages given in table 2 are based on the actual records 

 of daily divisions in all series, the individuals being isolated daily 

 and fed on the same fresh, standardized culture medium. In 

 some periods, notably in periods 20 and 21, and again in 25, the 

 averages are conspicuously out of proportion with those before 

 and after. These low averages, occurring in all series at exactly 

 the same time, but in different phases of the life cycles, are 

 obviously due to external conditions. The 20th and 21st periods 

 fell on May 28th to June 17th. On the 29th of May the cultures 

 were transferred from New York to Woods Hole, where a dif- 

 ferent natural water was used in making the culture medium, 

 and the temperature also was considerably lower than it had 

 been in New York. This unusual variation in the sequence of 

 averages makes no difference in the life cycle of a given series, 

 but if we wish to compare similar stages in the cycles of all series, 

 some of which include this period of adverse conditions while 

 others do not, it is obvious that a correction of the lower averages 

 is imperative. Such corrctions are made for all series in the 20th 

 and 21st periods by averaging the 18th and the 22nd to obtain 

 the 20th, and the 19th and 23rd to get the 21st. In making such 

 corrections the records of the individual lines are used and the 

 rate for each line is corrected; these corrected line averages are 

 then averaged to obtain the corrected average for the series. 

 The same method is employed for other periods in which cor- 

 rections are necessary. In table 2 such corrected averages are 

 included in brackets, and the corrected averages are used in 

 plotting curves of the life cycles and for comparison of different 

 series in similar phases of the cycle. 



