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ing out this view, science has, of course, many diffi- 

 culties to contend with. In the first place, the 

 subject of variation in existing life-forms has not yet 

 received sufficiently exact attention, nor has observa- 

 tion been extended over an adequate amount of time ; 

 and, in the second place, palaeontology is so recent, 

 and has so wide a field before it, that little more than 

 the outline of a plan of ascent from lower to higher 

 in time has been sketched by its cultivators. Under 

 these circumstances some may ascribe too much to 

 the influence of external conditions ; some to the 

 principle of natural selection, by which the weaker 

 and less elastic succumb to change of condition, while 

 the stronger and more elastic endure ; others to the 

 use and disuse of organs by which some members are 

 largely developed, and others gradually disappear ; and 

 others again, while admitting all these, may believe 

 that there are other factors in the law of development, 

 by which the whole scheme of life is kept in the midst 

 of incessant variation, even in consonance with a 

 great pre-ordained plan. But however the advocates 

 of development may difi'er on particulars, or how 

 much they may admit the imperfections of the theory, 

 they seek to establish it as the only comprehensible 

 process by which the Creator has chosen to people 

 this earth, at the several stages of its existence, with 

 newer, higher, and ever- varying life-forms. This is the 



