upon the doctrine of evolution, it
appeared to me that the _Anchitherium_, 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 metamorphosis, 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 metamorphosed 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.[3]

And, hence, I have ever since held that these facts afford evidence of
the occurrence of evolution, which, in the sense already defined, may be
termed demonstrative.

All who have occupied themselves with the structure of _Anchitherium_,
from Cuvier onwards, have acknowledged its many points of likeness to a
well-known genus of extinct Eocene mammals, _Palaeotherium_. Indeed, as
we have seen, Cuvier regarded his remains of _Anchitherium_ as those of
a species of _Palaeotherium_. Hence, in attempting to trace the pedigree
of the horse beyond the Miocene epoch and the Anchitheroid form, I
naturally sought among the various species of Palaeotheroid animals for
its nearest ally, and I was led to conclude that the _Palaeotherium
minus_ (_Plagiolophus_) represented the next step more nearly than any
form then known.

I think that this opinion was fully justifiable; but the progress of
investigation has thrown an unexpected light on the question, and has
brought us much nearer than could have been anticipated to a knowledge
of the true series of the progenitors of the horse.

You are all aware that, when your country was first discovered by
Europeans, there were no traces of the existence of the horse in any
part of the American continent. The accounts of the conquest of Mexico
dwell upon the astonishment of the natives of that country when they
first became acquainted with that astounding phenomenon--a man seated
upon a horse. Nevertheless, the investigations of American geologists
have proved that the remains of horses occ