156 LIFE AND DEATH. [III. 



their duration was limited to that of a single cell-generation, — 

 so it must have been possible for them, at a later period and if 

 the necessity arose, to lengthen their duration over two, three, 

 or more generations. And if my theory of the duration of life 

 in the Mctazoa is well founded, these cells have as a matter 

 of fact increased their duration, to an extent about equal to 

 that of the organism to which they belong. There is no ground 

 whatever for the assumption that it is impossible to fix the 

 number of cell-generations at infinity, — as actually happens in 

 the case of the reproductive cells, — but on the other hand it 

 has already been shown to be obvious that such an extension 

 is opposed to the principle of utility. It could never be to 

 the advantage of a species to produce crippled individuals, and 

 therefore the infinite duration of individuals has never re- 

 appeared among the Metazoa. So far the limited duration of 

 Metazoan life may be attributed to the worthlessness or even 

 the injurious nature of individuals, which although immortal, 

 were nevertheless liable to wear and tear. This fact explains 

 why immortality has never reappeared, it explains the pre- 

 dominance of death, but it was not the single primary cause 

 of this phenomenon. The perishable and vulnerable nature of 

 the soma was the reason why nature made no effort to endow 

 this part of the individual with a life of unlimited length. 



Gotte considers that death is inherent in reproduction, and 

 in a certain sense this is true, but not in the general way 

 supposed by him. 



1 have endeavoured to show above that it is most advanta- 

 geous for the preservation of the species among the lowest 

 Metazoa that the body should consist of a relatively small 

 number of cells, and that the reproductive cells should ripen 

 simultaneously and all escape together. If this conclusion 

 be accepted, the uselessness of a prolonged life to the somatic 

 cells is obvious, and the occurrence of death at the time of the 

 extrusion of the reproductive cells is explained. In this 

 manner death (of the soma) and reproduction arc here made to 

 coincide. 



This relation of reproduction to death still exists in a great 

 number of the higher animals. But such an association, 

 together with the simultaneous ripening of the reproductive 

 cells, has not been maintained continuously in the past. As 



