88 REMARKS ON CERTAIN [XI. 



facts of" the case, we see, on the one side, unicellular animals 

 which continually increase by division, and, on the other, multi- 

 cellular animals which are differentiated into somatic and 

 germ-cells, — animals in which the body dies, while the re- 

 productive cells possess the same power of unlimited increase 

 by division that is possessed by unicellular beings. But what 

 leads us to consider that the capacity for continuous reproduction 

 is rendered possible by the fusion of the essential material of 

 one organism with that of another, such as we see in both 

 conjugation and fertilization? Nothing but the unconscious 

 tradition of the inevitability of death. Maupas thinks that he 

 has proved the existence of natural death among the Infusoria, 

 since he has shown by his investigations, — excellent as far as 

 observation is concerned, — that, from time to time, conjugation 

 must make its appearance, or the colony would die out ; but he 

 forgets that as a matter of fact under natural conditions, the 

 possibility of conjugation is granted, and that thus the so- 

 called natural death does not appear more often in nature than 

 in the case of those metazoan ova which fail to meet with a 

 spermatozoon. The Infusorian which has not conjugated 

 gradually disappears, like the animal ^gg which rem.ains un- 

 fertilized; and the so-called ' senile degeneration ' (Maupas) of 

 the former exactly corresponds to the gradual decomposition 

 and dissolution of the latter, a process which was described 

 long ago, in a species of MoJna, in one of my memoirs on the 

 Daphnids. Conjugation, no less than fertilization, is un- 

 doubtedly a process of vast importance ; but I believe that its 

 significance lies in the maintenance and continual intermingling 

 of individual variations, or it may be that some other advan- 

 tage is conferred which acts for the preservation of the species. 

 In any case nature attaches great importance to it, and seeks 

 to ensure it, for each species, to the greatest possible extent. 

 For this purpose she has made provision that the periodical 

 recurrence of the process should affect as many individuals as 

 possible. If however, in spite of every provision, unfavourable 

 circumstances should bring it about that certain individuals have 

 no part in the process of conjugation, is it to be wondered at 

 that nature should care nothing for their preservation ? Or, to 

 speak less figuratively, we must not be surprised to see that 

 means are taken to prevent the unlimited increase of those 



