THE BEGINNINGS OF LIFE. 



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165 



with the inherent tendencies of the lowest living 

 things, would predispose towards their evolution into 

 unicellular organisms — both animal and vegetable. 

 And similar determining causes might be presumed 

 to be in part operative in the production of those 

 higher organisms which are composed of variously 

 arranged aggregates of such morphological units. But 

 we must not forget, as Mr. Spencer reminds us, that 

 from the Law of Heredity^ considered as extending to 

 the entire succession of large groups of living things 

 on the surface of our globe, during its whole past 

 history, <■ it follows that since the formation of these 

 small simple organisms must have 



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mation of larger 



have preceded the for- 

 and more complex organisms, the 

 larger and more complex organisms must inherit their 

 essential characters. We may anticipate,' Mr. Spencer 

 continues, ' that the multiplication and combination of 

 these minute aggregates or cells will be conspicuous 

 in the early developmental stages of plants and animals j 

 and that throughout all subsequent stages, cell-produc- 

 tion and cell-differentiation will be dominant charac- 

 teristics. The physiological units peculiar to each 

 higher species will, speaking generally, pass through 

 this form of aggregation on their way towards the 

 final arrangement they are to assume- because those 

 primordial physiological units from which they are 

 remotely descended, aggregated into this form. And 

 yet, just as' in other cases we found reason for in- 

 ferring (§ 131) that the traits of ancestral organization 



