26o THE EVOLUTION OF SEX. 



by observation ; a priori reasoning is here futile. The most 

 serious criticism of Weismann's view is due to Maupas. 

 Already we have noted his important result, that conjugation is 

 essential to the youth of the species. Without this incipient 

 sexual reproduction, the individuals in the course of numerous 

 successive asexual generations grow old. The nucleus degen- 

 erates, the size diminishes, the entire energy wanes, the senility 

 ends in death. Maupas believes that all organisms are fated to 

 suffer decay and death, and protests strongly against Weis- 

 mann's theory that death begins with the Metazoa. 



It must be noted, however, that in natural conditions the 

 conjugation, prohibited in Maupas's experiments, occurs when 

 it is wanted, and the life flows on. Furthermore, conjugation 

 has not been shown to occur in many Protozoa. It seems 

 therefore more warrantable to insert jMaupas's result as a saving 

 clause to Weismann's doctrine, than to regard it as contra- 

 dictory. The conclusion at present justifiable, is that Protozoa 

 not too highly differentiated, living in natural conditions 

 where conjugation is possible, have a freedom from natural 

 death. To this must then be added the demonstrated saving 

 clause, that in ciliated infusorians, conjugation, which here 

 means an exchange of nuclear elements, is the necessary con- 

 dition of eternal youth and immortality. 



Accepting then, with an emphasised proviso, the general 

 conclusion that most, if not all, unicellular organisms enjoy 

 immortality, that in being without the bondage of a " body " 

 they are necessarily freed from death, we pass to consider the 

 second question. What does the death of the higher and multi- 

 cellular organisms really involve? 



If death do not naturally occur in the Protozoa, it is evident 

 that it cannot be an inherent characteristic of living matter. 

 Yet it is universal among the multicellular animals. Death, 

 we may thus say, is the price paid for a body, the penalty its 

 attainment and possession sooner or later incurs. Now, by a 

 body is meant a complex colony of cells, in which there is 

 more or less division of labour, where the component units are 

 no longer, like the Protozoa, in possession of all their faculties, 

 but through division of labour have only restricted functions 

 and limited powers of self-recuperation. Like Maupas's isolated 

 family of infusorians, the cells of the body do not conjugate 

 with one another ; and though they divide and redivide for a 

 season, the life eventually runs itself out. 



