XIII THE GEOLOGICAL EVIDENCES OF EVOLUTION 389 



reason for the extinction has yet been given. Besides the 

 characters I have mentioned, there are many others in the 

 skeleton, skull, teeth, and brain of the forty or more inter- 

 mediate species, which show that the transition from the 

 Eocene Eohippus to the modern Equus has taken place in the 

 order indicated " ^ (see Fig. 33). 



Well may Professor Huxley say that this is demonstrative 

 evidence of evolution ; the doctrine resting upon exactly as 

 secure a foundation as did the Copernican theory of the 

 motions of the heavenly bodies at the time of its promulga- 

 tion. Both have the same basis — the coincidence of the 

 observed facts with the theoretical requirements. 



Development of Deer's Horns. 



Another clear and unmistakable proof of evolution is 

 afforded by one of the highest and latest developed tribes of 

 mammals — the true deer. These differ from all other ruminants 

 in jDossessing solid deciduous horns which are always more or 

 less branched. They first appear in the Middle Miocene 

 formation, and continue down to our time ; and their develop- 

 ment has been carefully traced by Professor Boyd Dawkins, 

 who thus summarises his results : — 



"In the middle stage of the Miocene the cervine antler 

 consists merely of a simple forked crown (as in Cervus dicro- 

 ceros), which increases in size in the Upper Miocene, although 

 it still remains small and erect, like that of the roe. In Cervus 

 Matheroni it measures 11 "4 inches, and throws off not more 

 than four tines, all small. The deer living in Auvergne in 

 the succeeding or Pliocene age, present us "vvith another stage 

 in the history of antler development. There, for the first 

 time, Ave see antlers of the Axis and Rusa type, larger and 

 longer, and more branching than any antlers were before, and 

 possessing three or more well-developed tines. Deer of this 

 type abounded in Pliocene Europe. They belong to the 

 Oriental division of the Cervidse, and their presence in Europe 

 confirms the evidence of the flora, brought forward by the 

 Comte de Saporta, that the Pliocene climate was warm. 

 They have probably disappeared from Europe in consequence 



^ Lecture on the Introduction and Succession of Vertebrate Life in America, 

 Nature, vol. xvi. p. 47L 



