168 PROTOZOOLOGY 



November 17, 1917, a series of pure-line cultures was established by 

 the daily isolation method. It was found that no series lived longer 

 than a year, but when two of the progeny of a series were allowed to 

 conjugate after the first 75 generations, the exconjugants repeated 

 the history of the parent series, and did not die when the parent 

 series died. In this way, lines of the same organism have lived for 

 more than 12 years, passing through numerous series. In a series, 

 the average division for the first 60 days was 15.4 divisions per 10 

 days, but the rate gradually declined until death. Woodruff and 

 Spencer (1924) also found the isolation cultures of Spathidium 

 spatula (fed on Colpidium colpoda) died after a gradual decline in 

 the division rate, but were inclined to think that improper environ- 

 mental conditions rather than internal factors were responsible for 

 the decline. 



On the other hand. Woodruff (1932) found that 5071 generations 

 produced by binary fission from a single individual of Paramecium 

 aurelia between May 1, 1907 and May 1, 1915, did not manifest 

 any decrease in vitality after eight years of uninterrupted asexual 

 reproduction without conjugation. With a race of P. caudatum, 

 Metalnikov (1924) observed a similar continued asexual reproduc- 

 tion. Dawson (1919) subjected an amicronucleate race of Oxytricha 

 hymenostoma to isolation culture and found that it declined in divi- 

 sion-rate and finally died out; but in mass cultures, the organisms 

 lived indefinitely. He attributed the decline in isolation culture to 

 improper environmental conditions. With Actinophrys sol Belaf 

 (1924) carried on isolation cultures (thus preventing paedogamy (p. 

 164) for 1244 generations for a period of 32 months and noticed no 

 decline in the division rate. Hartmann (1921) made a similar obser- 

 vation on Eudorina elegans. 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. 127) and that this elimination, 

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

 sion to carry on their metabolic functions more actively. 



