378 H. S. JENNINGS 



Our main results may then be summed up as follows : So far as 

 physiological effects are concerned, conjugation does not produce 

 rejuvenescence, for after conjugation most of the animals are less 

 vigorous than before. What conjugation does is to bring about 

 new combinations of germ plasm, just as is done in the sexual repro- 

 duction of higher animals. One result of this is to produce biparental 

 inheritance; another is to give origin to many variations, in the sense 

 of inherited differentiations between different strains. Some of the 

 new combinations are better adapted to the existing conditions than 

 others; these survive while the others die out. 



LITERATURE CITED 



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Calkins, G. N. 1902. Studies on the life-history of Protozoa. I. The life- 

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1906. The protozoan life-cycle. Biol. Bui., vol. 11, pp. 229-244. 

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