CHAPTER V. 



THE IMMORTALITY OF THE PROTOZOA. 



Impossibility of life without evolution Law of increase and 

 division Immortality of the protozoa Death, a pheno- 

 menon of adaptation which has appeared in the course of 

 the ages The infusoria The death of the infusoria Two 

 kinds of reproduction The caryogamic rejuvenescence of 

 Maupas Calkins on rejuvenescence Causes of senescence 

 Impossibility of life without evolution. 



WE take into account, a priori, the conditions that 

 must be fulfilled by the monocellular being in order 

 to escape the inevitability of evolution, of the succes- 

 sion of ages, of old age, and of death. It must be 

 able indefinitely to maintain itself in a normal regime, 

 without changing, without increasing, maintaining its 

 constant morphological and chemical composition, in 

 an environment vast enough for it to be unaltered by 

 the borrowings or the spendings resulting from its 

 nutrition i.e., it must remain constant in the presence 

 of the constant being. We might conceive of a 

 nutrition perfect enough, of exchanges exact enough, 

 and regular enough, for the state of things to be 

 indefinitely maintained. This would be absolute 

 permanence realized in the vital mobility. 



The Law of Growth and Division. This model of 

 a perfect and invariable machine does not exist in 

 nature. Life is incompatible with the absolute per- 

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