We have here, then, a series of generic types; for the true relations of which to each other we are indebted to the insight of such workers as Huxley and Marsh and Lartet, and others. They do not afford us illustrations of the minute and scarcely observable modifications which the law of the origin of species involves; they present us rather with a series of family groups; but the relation between them is such as to leave the mind accustomed to biological investigations convinced, that, could we see all the forms that occurred between them, there could be no question as to the origin of these forms, from _eohippus_ of the oldest eocene beds to _equus_ of to-day. Unlike as in a general sense they are, they are progressive modifications, with higher and higher specializations, until, in the extant horse, the highest special modification is attained. It will harmonize with no dogma of theology, and no doctrine of science, to assume that these equine forms, separated by such enormous epochs of time, were specially created: all accurate knowledge forbids the supposition; while varieties sufficiently marked, such as the race-horse, the giant and powerful dray-horse, the Shetland and the Norman ponies, known to be derived from a common parentage, give the clearest sanction to the inference, that what we now know of the geological history of the horse proves it to be a product of the Darwinian law of evolution; that there has been no total destruction of equine (or any other) life in the great past; but that there has been a continuity of it, borne from region to region, and modified continuously by a thousand changing circumstances. Consequently we find, in the rocky records of the past, that organic types become simpler, and liker to each other, as we trace them through the incomplete geological record to a dim and far off age. Here, then, we have a series of such generalized types, plainly related to each other in time, leading us down from the horse of historic times to less and less specialized forms of it, as the epoch grows more remote; until in the upper mesozoic or lower eocene beds, we find the progenitor of the line of the equine types we know, to be an animal with a splay foot of five toes, adapted to slow movement in a boggy soil. The slow specialization adapted it to increasing rapidity and ease of movement, and modified states of soil; acting, without doubt, as an increasing protection against its enemies, and providing it with an ever surer means of obtaining abundant and suitable food. And beneficial variation continued to act until the noble horse, beautiful in form, exquisitely graceful in action, and swift as the wind, had been thus created.