DEATH 287 



Metazoa the power appears to be lost very early by 

 the majority of the cells, and retained only by the 

 reproductive cells. This however does not in any 

 way invalidate the comparison, and is merely an 

 example of that structural and physiological differ- 

 entiatiation which distinguishes Metazoa from 

 colonial Protozoa, and which affords the key to all 

 Metazoon structure. 



Moreover, it is at present entirely unknown to 

 us at what period or to what extent somatic cells of 

 a Metazoon lose their power of conjugating. From 

 this standpoint it would be of the greatest interest 

 to know precisely what happens in cases of intro- 

 duction of cells from without into a living Metazoon; 

 for example, in vaccination or in other methods of 

 inoculation ; or in cases of transfusion of blood on 

 a large scale. Theoretically it seems possible that 

 rejuvenescence of the somatic, as of the reproductive 

 cells of a Metazoon might be effected, and a new 

 lease of life obtained for these cells and their 

 descendants. This however is a matter of mere 

 speculation, and not to be lightly entered upon. 

 The general conclusions to which these recent 

 investigations have led us may be briefly summarised 

 as follows : 



i. Death is not an intrinsic necessity, either 



of life or of organisation, 

 ii. .Natural death first appeared, so far as we 

 know at present, among the higher 

 Protozoa. 



iii. Death is closely associated with the occur- 

 rence of conjugation, and the consequent 



