all the quadrupeds,
in birds, in fishes, and we may find traces of them as far down as the
turtle, in which they seem still to be sketched out by means of furrows
that are to be found beneath the shell. Let it be remembered that the
foot of the horse, which seems so different from a man's hand, is,
nevertheless, as M. Daubenton has pointed out, composed of the same
bones, and that we have at the end of each of our fingers a nail
corresponding to the hoof of a horse's foot. Judge, then, whether this
hidden resemblance is not more marvellous than any outward
differences--whether this constancy to a single plan of structure which
we may follow from man to the quadrupeds, from the quadrupeds to the
cetacea, from the cetacea to birds, from birds to reptiles, from
reptiles to fishes--in which all such essential parts as heart,
intestines, spine, are invariably found--whether, I say, this does not
seem to indicate that the Creator when He made them would use but a
single main idea, though at the same time varying it in every
conceivable way, so that man might admire equally the magnificence of
the execution and the simplicity of the design.[46]

"If we regard the matter thus, not only the ass and the horse, _but even
man himself, the apes, the quadrupeds, and all animals might be regarded
but as forming members of one and the same family_. But are we to
conclude that within this vast family which the Creator has called into
existence out of nothing, there are other and smaller families,
projected as it were by Nature, and brought forth by her in the natural
course of events and after a long time, of which some contain but two
members, as the ass and the horse, others many members, as the weasel,
martin, stoat, ferret, &c., and that on the same principle there are
families of vegetables, containing ten, twenty, or thirty plants, as the
case may be? If such families had any real existence they could have
been formed only by crossing, by the accumulation of successive
variations (_variation successive_), and by degeneration from an
original type; but if we once admit that there are families of plants
and animals, so that the ass may be of the family of the horse, and
that the one may only differ from the other through degeneration from a
common ancestor, we might be driven to admit that the ape is of the
family of man, that he is but a degenerate man, and that he and man have
had a common ancestor, even as the ass and horse have