:;:;i 



BIOLOGY OF THE PROTOZOA 



following synoptic table shows not only these facts but also that 

 for Uroleptus mobilis vitality may be maintained at an optimum 

 by conjugations during youthful periods of consecutive series (see 

 also Fig. 166). Experimental data show that parthenogenesis 

 (endomixis) also brings about a similar restoration to an optimum 

 vitality. 



1. Renewal of Vitality as a Result of Conjugation.— In Chapter VII 

 it w T as shown that the life cycle of an ex-conjugant of Uroleptus 

 mobilis begins with high vitality; this gradually weakens during 

 a period of from nine to twelve months and ends with death of the 



Fig. 166. — Condensed vitality graphs showing the descent of Uroleptus mobilis from 

 November, 1917 to 1926. S = series; G = generation age of parents. 



last individual representing that protoplasm if reorganization by 

 fertilization or parthenogenesis has been prevented. A full pedigree 

 of a late series (12S) is illustrated by the graphs shown in Fig. 

 166. Conjugation between the progeny of an ex-conjugant occurs 

 whenever a conjugation test is made after the series is mature 

 (see p. 271). An ex-conjugant from such a mating has a higher 

 vitality as expressed by the division-rate than the individuals 

 of the parent series which had not conjugated. The test for this 

 is shown by a comparison of the division-rate of the parent proto- 

 plasm which has not conjugated with the division-rate of the 

 protoplasm that had conjugated, both protoplasms running simul- 



