DEATH 285 



which reproduce both by fission and by a sexual 

 process of conjugation there are definite limits to 

 the number of generations which can be produced 

 asexually; (ii.) that conjugation only occurs be- 

 tween individuals which are not nearly related to 

 each other ; (iii.) that if conjugation with unrelated 

 forms be prevented, senescence, and finally death 

 occur. 



These results are of the utmost interest in connec- 

 tion with Weismann's views regarding the nature 

 and origin of death. They show that Weismann 

 was wrong in supposing that death occurred first 

 amongst Metazoa. Natural death occurs among 

 Protozoa ; and the tendency to it and inability to 

 escape from it, are probably inherited by Metazoa 

 from their Protozoon ancestors. On the other hand, 

 Maupas' results confirm in the fullest manner Weis- 

 mann's bold suggestions, (i.) that the original 

 occurrence of death is intimately connected with 

 sexual reproduction, if not indeed an actual conse- 

 quence of it; (ii.) that the number of generations 

 of somatic cells which can succeed one another in 

 the course of a single life may be strictly limited. 

 Maupas' experiments seem to me to afford the very 

 evidence of which Weismann was in search. They 

 prove that amongst Infusoria asexual reproduction 

 by cell division cannot be continued indefinitely, but 

 that it leads in time to senescence and ultimately to 

 death. 



If we apply these results to Metazoa the conclu- 

 sions become very striking. In Metazoa, as in 

 Infusoria, there is alternation of sexual and asexual 



