100 DOCTRINE OF EVOLUTION 



bodies of evidence that they exemphfy, we learn how 

 surely the testimony of the rocks estabhshes evolution 

 in its own way, how it confirms the law of recapitulation 

 demonstrated by comparative embryology, and how 

 it proves that the greater and smaller divisions of 

 animals have followed the identical order in their 

 evolution that the comparative study of the present 

 day animals has independently described. 



The facts of geographical distribution constitute 

 the fifth division of zoology, and an independent 

 class of evidences proving the occurrence of evolution. 

 This department of zoology assumed its rightful status 

 only after the other divisions had attained considerable 

 growth. Many naturalists before Darwin and Wallace 

 and Wagner had noticed that animals and plants 

 were by no means evenly distributed over the surface 

 of the globe, but until the doctrine of evolution cleared 

 their vision they did not see the meaning of these facts. 

 As in the case of all the other departments of zoology 

 the immediate data themselves are familiar, but because 

 they are so obvious the mind does not look for their 

 interpretation but accepts the facts at their face value. 

 While the phenomena of distribution are no less fascinat- 

 ing to the naturalist, and no less effective in their dem- 

 onstration of evolution, their comprehensive treatment 

 would demand more space than the whole purpose of the 

 present description of organic evolution would justify. 

 Thus a brief outline only can be given of the saUent 

 principles of this subject in order that their bearing 

 upon the problem of species may be indicated. 



