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SUMMARY. 



sizes may represent those whole orders, families, and genera 

 which have now no living representatives, and which are 

 known to ns only in a fossil state. As we here and there 

 see a thin, straggling branch springing from a fork low down 

 in a tree, and which by some chance has been favored and is 

 still alive on its summit, so we occasionally see an animal 

 like the Ornithorhynchus or Lepidosiren, which in some 

 small degree connects by its affinities two large branches of 

 life, and which has apparently been saved from fatal compe- 

 tition by having inhabited a protected station. As buds give 

 rise by growth to fresh buds, and these, if vigorous, branch 

 out and overtop on all sides many a feebler branch, so by 

 generation I believe it has been with the great Tree of Life, 

 which fills with its dead and broken branches the crust of 

 the earth, and covers the surface with its ever-branching and 

 beautiful ramifications. • 



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