18 DARWimANA. 



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 afiinities of all the beings of the same class have some- 

 times' 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 spe- 

 cies. At each period of growth all the growing twigs have 

 tried to branch out on all sides, and overtop and kill the sur- 

 rounding 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 connection 

 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 flour- 

 ished 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 de- 

 scendants. From the first growth of the tree, many a limb and 

 branch has decayed and dropped ofi"; and these lost 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 from having been found 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 afiinities 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, Ijranch out 



