CHAPTER V.
THE IMMORTALITY OF THE PROTOZOA.
Impossibility of life without evolution—Law of increase and
division—Immortality of the protozoa—Death, a phenomenon
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 succession of ages, of old age, and of death. It must be able indefinitely to maintain itself in a normal régime, 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-
