Chap. IV. SUMMARY. 129 



ranked in a single file, but seem rather to be clustered 

 round points, and these round other points, and so on 

 in almost endless cycles. On the view that each spe- 

 cies has been independently created, I can see no 

 explanation of this great fact in the classification of all 

 organic beings ; but, to the best of my judgment, it is 

 explained through inheritance and the complex action 

 of natural selection, entailing extinction and divergence 

 of character, as we have seen illustrated in the diagram. 

 The affinities of all the beings of the same class have 

 sometimes been represented by a great tree. I believe 

 this simile largely speaks the truth. The green and 

 budding twigs may represent existing species ; and those 

 produced during each former year may represent the 

 long succession of extinct species. At each period of 

 growth all the growing twigs have tried to branch out 

 on all sides, and to overtop and kill the surrounding 

 twigs and branches, in the same manner as species and 

 groups of species have tried to overmaster other species 

 in the great battle for life. The limbs divided into 

 great branches, and these into lesser and lesser branches, 

 were themselves once, when the tree was small, budding 

 twigs ; and this connexion of the former and present 

 buds by ramifying branches may well represent the 

 classification of all extinct and living species in groups 

 subordinate to groups. Of the many twigs which flou- 

 rished when the tree was a mere bush, only two or 

 three, now grown into great branches, yet survive and 

 bear all the other branches ; so with the species which 

 lived during long-past geological periods, very few now 

 have living and modified descendants. From the first 

 growth of the tree, many a limb and branch has decayed 

 and dropped off; and these lost branches of various 

 sizes may represent those whole orders, families, and 

 genera which have now no living representatives, and 



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