and in all 

 - assisted 

 lolecula 



cas: 



s 



^i. 



V 



( 



r 



[ 



by other intei 

 f induced 



xtcrnal conditii 



n, however, wliet 



of the other pi- 



le 



. come into 



! 



of 'orga 



t la^vs 



1 of eflrects is 



|P^ 



similai t 



■ ' matter 

 Present day, 



J-' 



ticp 



1. 1; 



s 



urface 



of 0"^ r 



n s 



uch 



inatt^ 



'J 



g 



units 



w 



the 



wor 



ia'5 



s''', 



r^^ BEGINNINGS OF LIFE. 



639 



1 



must^ in each period, have given rise to innumerable 

 multitudes of what have been called ^ trees of life/ branch- 

 ing out into animal and vegetal forms of almost incon- 



ceivable variety- My 



^ trees/ including 



all their branches and innumerable ramifications, may 

 have wholly died out during the many vicissitudes of 

 the earth's surface and the long lapse of ever-fruitful 

 ao-eSp though the descendants or ultimate ramifications 

 of some of such trees — dating back to quite different 

 and perhaps far-distant epochs — may still survive 



upon 



the earth's surface. How far, however, the 



roots of any of those trees from which the existing 

 higher forms of life are derived, may have extended 

 back into the depths of geologic time, we are utterly 



unable to estimate. 



Throughout all this life -evolving period of the 

 history of our globe, the progress of ^ organization ' 

 seems to have been essentially similar. And that this 

 should be so, seems readily explicable by the 

 sideration that living 



con- 



things, both as regards their 



origin and their subsequent differentiation or deve- 

 lopment, are the immediate products of ever-acting 

 natural laws or material properties which are probably 

 the same now as they have ever been. 



The lower the forms of life — that is the nearer they 

 are to their source— the greater seems to have been 

 the similarity amongst those which have been produced 

 in different ages. On the other hand, the longer any 

 particular tree of life has lived (of which there have been 



> 



I 



