126 LECTURES ON EVOLUTION in 



upon the doctrine of evolution, it appeared to me 

 that the Anchitherium 9 the Hipparion, and the 

 modern horses, constitute a series in which the 

 modifications of structure coincide with the order 

 of chronological occurrence, in the manner in 

 which they must coincide, if the modern horses 

 really are the result of the gradual metamor- 

 phosis, in the course of the Tertiary epoch, of 

 a less specialised ancestral form. And I found 

 by correspondence with the late eminent French 

 anatomist and palaeontologist, M. Lartet, that he 

 had arrived at the same conclusion from the 

 same data. 



That the Anchitherium type had become meta- 

 morphosed into the Hipparion type, and the 

 latter into the Equine type, in the course of 

 that period of time which is represented by the 

 latter half of the Tertiary deposits, seemed to 

 me to be the only explanation of the facts for 

 which there was even a shadow of probability. 1 



And, hence, I have ever since held that these 

 facts afford evidence of the occurrence of evo- 

 lution, which, in the sense already defined, may 

 be termed demonstrative. 



1 I use the word " type " because it is highly probable that 

 many forms of Anchitherium-like and Hipparion-lik.Q animals 

 existed in the Miocene and Pliocene epochs, just as many species 

 of the horse tribe exist now ; and it is highly improbable that 

 the particular species of Anchitherium or Hipparion, which 

 happen to have been discovered, should be precisely those 

 which have formed part of the direct line of the horse's 

 pedigree. 



