Chap. IV.] SUMMARY. 163 



living and modified descendants. From the fiist growth 

 of the tree, many a limb and 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 

 favoured and is still alive on its summit, so we occa- 

 sionally see an animal like the Ornithorhynchus or 

 Lepidosiren, which in some small degree connects by its 

 aflBnities two large branches of life, and which has ap- 

 parently been saved from fatal competition 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 raanifications. 



