24 HEREDITY AND SELECTION IN SOCIOLOGY 



nated. Maupas, in his experiments, demonstrated that certain 

 Infusorians, when artificially prevented from conjugating, die 

 out. The death of the colony is slow, but sure, and Maupas 

 had no hesitation in ascribing it to senile decay ; for, when the 

 artificially imposed conditions were removed, and when con- 

 jugation set in again, the degeneration was effectually prevented, 

 and the colony was " rejuvenated." Maupas himself described the 

 phenomenon of conjugation as un rajeunissement haryogamique. 



The experiments of Maupas are not, however, as conclusive 

 as their author supposed them to be. Weismann has suggested 

 that it may very likely have been the unnatural conditions under 

 which Maupas maintained his colony during several months, 

 rather than the lack of conjugation, which caused their ultimate 

 decay and death. Weismann has himseli experimented with a 

 parthenogenetic species of crustacean, Cypris reptans, and 

 during sixteen years he was able to breed over eighty successive 

 generations without any amphimixis. Weismann rightly re- 

 marks that the alleged " rejuvenating " force of some former 

 amphimixis must, in this case, have been an extraordinarily 

 persistent one.^ 



The truth is that amphimixis, in the case of those species 

 which practise it, is an indispensable condition of development 

 and reproduction. Although asexual reproduction may continue 

 for a certain time, sooner or later amphimixis must again inter- 

 vene. But it is essentially a phenomenon sui generis. That it is 

 not universally indispensable to reproduction is proved by several 

 instances. A large number of Algse and Fungi are developed ex- 

 clusively from asexual spores, and the occurrence of partheno- 

 genetic eggs proves that even differentiated female reproductive 

 cells can, under certain circumstances, develop independently 

 of amphimixis. Certain Crustacea reproduce themselves solely 

 by parthenogenesis, and this is the more interesting, since it is 

 known that they formerly exhibited sexual reproduction, for the 

 ^ Weismann, Vortrage iiber Deszendenztheorie, i. 267 . 



