21 AMPHIMIXIS OR ESSENTIA I MEANING OF [XII. 



which may remain unanswered— it is enough that it was un- 

 necessary. 



In Protozoa unending life was an inevitable necessity for the 

 maintenance of the species. 



Potential immortality is found from the very lowest organ- 

 isms to the higher Protozoa and to the germ-cells of Metazoa 

 and Metaphyta ; but in the latter cases certain conditions are 

 imposed upon it, and these include not only the ordinary 

 conditions of nourishment, and of surrounding circumstance, 

 but, as a rule, the further condition of amphimixis. 



The Appearance of Amphimixis in the Organic World. 



If we are unable to discover any effect of amphimixis which 

 can render its prevalence intelligible, nothing remains but to 

 accept the rejuvenescence theory. For not only is amphimixis 

 found throughout the whole organic world so far as we know it, 

 but the entire form of the latter has been controlled in a most 

 fundamental manner, and, without amphimixis, would have been 

 utterly different. 



It has been shown above that the occurrence of an ontogeny 

 in the Metazoa essentially depends upon the necessity for 

 amphimixis ; since this presupposes the concentration of the 

 collective hereditary tendencies of a species in the nucleus of 

 a single cell. But this is not only true of all the varied kinds of 

 direct ontogeny: the complex and changing forms of alternation 

 of generation in animals and plants are also, mainly and in the 

 most important respects, dependent on the necessity for making 

 amphimixis possible. I say ' necessity,' because I hold that 

 everything real is also necessary, and that this is true even 

 of the things we generally call useful ; for I beHeve that in 

 nature the really useful — viz. that which is useful when con- 

 sidered in relation with the whole of its consequences and not 

 by itself alone — is also invariably necessary. The useful becomes 

 necessary as soon as it is possible. In this sense we may regard 

 amphimixis as necessary because it obviously involves a deep 

 and essential use. 



Its unusually elastic powers of adaptation show how far it 

 is from being necessary, viz. essential to life, in the usual sense 

 of the word. 



If amphimixis is truly rejuvenescence, i.e. the hindering of an 



