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T/Ii; BEGINNINGS OF LIFE, 



607 



may 



regard them as 



more or less recent products of 



Archebiosis and Heterogenesis. 



We do not pretend to fix the limits of ephem^ro- 

 morphism and to say, on all sides, .where true 



we may expect that much 



though 



species begin 



Hght will be thrown upon this subject by subsequent 



workers. It is only natural, however, to suppose 



that the transitions from 



heterogenesis and 



meta- 



morphism to homogenesis and specific fixity should 

 be more or less 



gradual ; 



so that many forms will 

 have to remain, as it were, upon the border-land. 

 Ascending development amongst the ephemeromorphs 

 tends to lead to the production of more complex and 

 less variable forms. But even long after the fir-st rudi- 

 ments of a sexual generation have been arrived at, and 

 the origin of ^species' has commenced, we might ex- 

 pect that the comparatively unspecialized matter of 



which 



such organisms are 



composed, and the com- 

 parative weakness of the internal conservative prin- 

 ciple (essentially based, as it is, upon heredity and 

 complexity of organization), would permit of their under- 

 going marked variations from time to time, either under 

 the influence of changed external conditions or by virtue 

 of ^ spontaneously ' initiated internal changes ^ 



^ Mr. Darwin's view is directly opposed to this ; for instance, after 

 speaking of fresh-water productions, and the fact that many of them are 

 low in the scale of nature, he adds (loc. cit., p. 467) :- ' We have reason 

 to believe that such low beings change or become inodlfied less quickly than 

 the high,' And to show that this is no mere casual expression of 

 opinion^ we find Mr. Darwin saying in the last page but one of his 



