NATURAL SELECTION 107 



branch has decayed and dropped off; and these fallen branches 

 of various sizes may represent those whole orders, families, and 

 genera which have now no living representatives, and which are 

 known to us 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 af- 

 finities two large branches of life, and which has apparently been 

 saved from fatal competition by having inhabited a protected sta- 

 tion. As buds give rise by growth to fresh buds, and these, if vig- 

 orous, 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 rami- 

 fications. 



