XI.] PROBLEMS OF THE DAY. 87 



cling to this view, and Maupas^ has recently claimed to have 

 found a proof of its soundness by showing that it is essential 

 for Infusoria to conjugate (sexual reproduction) from time to 

 time. 



This contention forms a striking example of the difficulty 

 with which even scientifically trained minds can shake off 

 deeply rooted convictions. Although it must be clear to every 

 one that unicellular organisms are immortal, although Maupas 

 has himself produced superabundant proofs that the repro- 

 duction of Infusoria by fission can go on without ceasing, and 

 although he maintains that ' les cycles evolutifs des Cilies 

 peuvent se succeder a I'infini ' (p. 437), nevertheless the 

 power of the old tradition of the necessity of death is so strong 

 in him that he is incapable of recognizing this simple fact. 

 Rather than adopt the views propounded by others, he prefers 

 to accept the hypothesis that unicellular organisms are really 

 mortal and are subject to natural death, but that this is kept 

 in abeyance and postponed by the influence of conjugation. 



If we ask, whence comes this idea of the necessity of death, 

 we receive the answer, — from our experience of man and the 

 higher animals and plants. If we further ask, why has it hitherto 

 been entirely overlooked that among these organisms certain 

 parts of the body (the reproductive cells) are endowed with 

 immortality, the answer is,— because we have only recently 

 come to know and completely appreciate the facts of reproduc- 

 tion, and therefore have only just arrived at a correct estimate 

 of them, and are now for the first time able to recognize in our 

 reproductive cells, the undying parts of our individuality. 



For how long then will reproduction be regarded as a dy- 

 namical process, as a stimulus, as ' the spark in the powder 

 cask,' or in biological language the vitalizing of the Q.%g ? This 

 conception is directly derived from the old vital force of earlier 

 times, and it is the unrecognized reflection of this latter idea 

 which influences many writers, and which, proteus-like, con- 

 tinually appearing in new forms, evokes the belief in a necessity 

 for the rekindling of life. 



If we lay aside preconceived notions and simply review the 



^ E. Maupas, ' Le rajeunissement karyogamique chez les Cilies,' Arch. 

 Zool. exper. et generale, 2 ser., Tom. vii. Nr. i, 2, et 3, 1889. 



