Since his earlier lectures to the public on evolution, the paleontological evidences had been accumulating; the case could be stated without some of the reservations of former days; and he brings forward two telling instances in considerable detail, the one showing how the gulf between two such apparently distinct groups as Birds and Reptiles is bridged over by ancient fossils intermediate in form; the other illustrating from Professor Marsh’s new collections the lineal descent of the specialised Horse from the more general type of quadruped.

The farthest back of these was a creature with four toes on the front limb and three on the hind limb.  Judging from the completeness of the series or forms so far, he ventured to indulge in a prophecy.]

Thus, thanks to these important researches, it has become evident that, so far as our present knowledge extends, the history of the horse-type is exactly and precisely that which could have been 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; 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.

[Seldom has prophecy been sooner fulfilled.  Within two months, Professor Marsh had discovered a new genus of equine mammals, Eohippus, from the lowest Eocene deposits of the West, which corresponds very nearly to the description given above.

He continues:—­]

That is what I mean by demonstrative evidence 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 foundation as the Copernican theory of the motions of the heavenly bodies did at the time of its promulgation.  Its logical basis is of precisely the same character—­the coincidence of the observed facts with theoretical requirements.

[He left New York on September 23.] “I had a very pleasant trip in Yankee-land,” [he writes to Professor Baynes,] “and did not give utterance to a good deal that I am reported to have said there.” [He reached England in good time for the beginning of his autumn lectures, and his ordinary busy life absorbed him again.  He did not fail to give his London audiences the results of the recent discoveries in American paleontology, and on December 4, delivered a lecture at the London Institution, “On Recent Additions to the Knowledge of the Pedigree of the Horse.”  In connection with this he writes to Professor Marsh:—­]