EEJUVENESCENCE IN UROLEPTUS MOBILIS 127 



generation, and is still living in the 254th generation. The L 

 series, or first F4 series, started as an ex-conjugant on November 

 3, 1918, from the I series in the 199th generation (the grand- 

 parent F series was in the 294th generation, the great-grand- 

 parent C series was in the 347th generation, and the great-great- 

 grandparent A series was dead). This series, also, is active, and 

 in the 196th generation. The M series started from a cyst of 

 the F series which had encysted on April 27th while in the 45th 

 generation, remained dry for more than six months, and was 

 recovered from the cyst on November 18, 1918. The N series 

 was started on December 12, 1918, as an ex-conjugant from the J 

 series in the 188th generation. The series was started as an 

 ex-conjugant on January 10, 1919, from the M series in the 105th 

 generation. The P series was started on January 12, 1919, as an 

 ex-conjugant of the L series in its 115th generation. The Q 

 series was started on January 19, 1919, as an ex-conjugant of the 

 I series in its 316th generation. Finally, the R series was 

 started as an ex-conjugant on January 19, 1919, from the J series 

 in its 245th generation. 



In addition to these fourteen series representing one proto- 

 plasm, two other series, representing a different initial proto- 

 plasm, have been followed throughout the life history. Of these 

 the B series started from an encysted 'wild' Uroleptus mobilis. 

 This individual encysted on November 9, 1917, remained dry 

 from December 1st until January 24th, when it was recovered 

 from the cyst. A filial series, the G series, started as an ex- 

 conjugant from the B series in the 115th generation on March 

 23rd, and died out on January 5th, 1919, in the 291st generation. 



In computing the division rate of a series for a given period, 

 e.g., ten days, the number of divisions in all five lines for the ten 

 days are added and the sum divided by five. The value of such 

 an average depends somewhat on the extent of variation in 

 number of divisions in each of the five lines. In table 1 the indi- 

 vidual line records for six consecutive ten-day periods from June 

 27th to August 25th and for all the series under observation 

 during this sixty-day period are given. Since the different series 

 were started from ex-conjugants at different times, this sixty- 



