to reptiles on the other.

The only instance in which an approach towards a series of nearly related
forms has been obtained is the existing horse, its predecessor Hipparion
and other extinct forms. But even here there is no proof whatever of
modification by minute and infinitesimal steps; _a fortiori_ no approach to
a proof of modification by "Natural Selection," acting upon indefinite
fortuitous variations. On the contrary, the series is an admirable example
of successive modification in one special direction along one beneficial
line, and the teleologist must here be allowed to consider that one {134}
motive of this modification (among probably an indefinite number of motives
inconceivable to us) was the relationship in which the horse was to stand
to the human inhabitants of this planet. These extinct forms, as Professor
Owen, remarks,[129] "differ from each other in a greater degree than do the
horse, zebra, and ass," which are not only good _zoological_ species as to
form, but are species _physiologically_, _i.e._ they cannot produce a race
of hybrids fertile _inter se_.

As to the mere action of surrounding conditions, the same Professor
remarks:[130] "Any modification affecting the density of the soil might so
far relate to the changes of limb-structure, as that a foot with a pair of
small hoofs dangling by the sides of the large one, like those behind the
cloven hoof of the ox, would cause the foot of Hipparion, _e.g._, and _a
fortiori_ the broader based three-hoofed foot of the Palaeothere, to sink
less deeply into swampy soil, and be more easily withdrawn than the more
concentratively simplified and specialized foot of the horse. Rhinoceroses
and zebras, however, tread together the arid plains of Africa in the
present day; and the horse has multiplied in that half of America where two
or more kinds of tapir still exist. That the continents of the Eocene or
Miocene periods were less diversified in respect of swamp and sward, pampas
or desert, than those of the Pliocene period, has no support from
observation or analogy."

Not only, however, do we fail to find any traces of the incipient stages of
numerous very peculiar groups of animals, but it is undeniable that there
are instances which appeared at first to indicate a _gradual transition_,
yet which instances have been shown by further investigation and discovery
not to indicate truly anything of the kind. Thus at one time the remains of
Labyrinthodonts,