154 LIFE AND DEATH. 



When the somatic cells of the first Heteroplastides ceased to be 

 immortal, such a loss would not in any way have precluded them 

 from regaining- this condition. Just as, with the differentiation of 

 the first somatic cells of the lowest Heteroplastides, 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 Metazoa 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 reappeared 

 among the Metazoa. So far the limited duration of Meta- 

 zoan 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 im- 

 mortality has never reappeared, it explains the predominance 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. 



I have endeavoured to show above that it is most advantageous 

 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 conchision 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 

 are here made to coincide. 



This relation of reproduction to death still exists in a great num- 



