210 PROTOZOOLOGY 



Hartmann (1921) made a similar observation on Eudorina 



It would appear that in these forms, the life continues indefinitely 



without apparent decrease in vital activity. 



As has been noted in the beginning part of the chapter, the 

 macronucleus in the ciliates undergoes, at the time of binary fission 

 a reorganization process before dividing into two parts and undoubt- 

 edly, there occurs at the same time extensive cytoplasmic reorgani- 

 zation as judged by the degeneration and absorption of the old, and 

 formation of the new, organellae. It is reasonable to suppose that 

 this reorganization of the whole body structure at the time of divi- 

 sion is an elimination process of waste material accumulated by the 

 organism during the various phases of vital activities as was con- 

 sidered by Kidder and others (p. 150) and that this elimination, 

 though not complete, enables the protoplasm of the products of divi- 

 sion to carry on their metabolic functions more actively. 



As the generations are multiplied, the general decline in vitality 

 is manifest not only in the decreased division-rate, slow growth, 

 abnormal form and function of certain organellae, etc., but also in 

 inability to complete the process involved in conjugation. Jennings 

 (1944) distinguished four successive periods in various clone cultures 

 of Paramecium bursaria; namely, (1) a period of sexual immaturity 

 during which neither sexual reaction nor conjugation occurs; (2) a 

 period of transition during which weak sexual reactions appear in a 

 few individuals; (3) a period of maturity in which conjugation takes 

 place readily when proper mating types are brought together; and 

 (4) a period of decline, ending in death. The length of the first two 

 periods depends on the cultural conditions. Exconjugant clones that 

 are kept in condition under which the animals multiply rapidly, 

 reach maturity in three to five months, while those subjected to de- 

 pressing condition require 10 to 14 months to reach maturity. The 

 third period lasts for several years and is followed by the fourth 

 period during which fission becomes slower, abnormalities appear, 

 many individuals die and the clones die out completely. 



Does conjugation affect the longevity of clones in Paramecium 

 busaria? A comparative study of the fate of exconjugants and non- 

 conjugants led Jennings (1944a) to conclude that (1) conjugation 

 results in production of one of the following four types: (a) excon- 

 jugants perish without division, (b) exconjugants divide one to four 

 times and then die, (c) exconjugants produce weak abnormal clones 

 which may become numerous, and (d) exconjugants multiply vigor- 

 ously and later undergo conjugation again; at times the latter are 



