132 LECTURES ON EVOLUTION in 



predicted from a knowledge of the principles of 

 evolution. And the knowledge we now possess 

 justifies us completely in the anticipation, that 

 when the still lower Eocene deposits, and those 

 which belong to the Cretaceous epoch, have yielded 

 up their remains of ancestral equine animals, we 

 shall find, first, a form with four complete toes and 

 a rudiment of the innermost or first digit in front, 

 with, probably, a rudiment of the fifth digit in the 

 hind foot; 1 while, in still older forms, the series of 

 the digits will be more and more complete, until 

 we come to the five-toed animals, in which, if the 

 doctrine of evolution is well founded, the whole 

 series must have taken its origin. 



That is what I mean by demonstrative evi- 

 dence of evolution. An inductive hypothesis is 

 said to be demonstrated when the facts are 

 shown to be in entire accordance with it. If 

 that is not scientific proof, there are no merely 

 inductive conclusions which can be said to be 

 proved. And the doctrine of evolution, at the 

 present time, rests upon exactly as secure a foun- 

 dation as the Copernican theory of the motions 

 of the heavenly bodies did at the time of its pro- 

 mulgation. Its logical basis is precisely of the 



1 Since this lecture was delivered, Professor Marsh has 

 discovered a new genus of equine mammals (Eohippus) from the 

 lowest Eocene deposits of the West, which corresponds very 

 nearly to this description. American Journal qf Science^ 

 November, 1876. 



