Take, again, another set of very remarkable facts,--the existence of
what are called rudimentary organs, organs for which we can find no
obvious use, in the particular animal economy in which they are found,
and yet which are there.

Such are the splint-like bones in the leg of the horse, which I here
show you, and which correspond with bones which belong to certain toes
and fingers in the human hand and foot. In the horse you see they are
quite rudimentary, and bear neither toes nor fingers; so that the horse
has only one "finger" in his fore-foot and one "toe" in his hind foot.
But it is a very curious thing that the animals closely allied to the
horse show more toes than he; as the rhinoceros, for instance: he has
these extra toes well formed, and anatomical facts show very clearly
that he is very closely related to the horse indeed. So we may say that
animals, in an anatomical sense nearly related to the horse, have those
parts which are rudimentary in him, fully developed.

Again, the sheep and the cow have no cutting-teeth, but only a hard pad
in the upper jaw. That is the common characteristic of ruminants in
general. But the calf has in its upper jaw some rudiments of teeth
which never are developed, and never play the part of teeth at all.
Well, if you go back in time, you find some of the older, now extinct,
allies of the ruminants have well-developed teeth in their upper jaws;
and at the present day the pig (which is in structure closely connected
with ruminants) has well-developed teeth in its upper jaw; so that here
is another instance of organs well-developed and very useful, in one
animal, represented by rudimentary organs, for which we can discover no
purpose whatsoever, in another closely allied animal. The whalebone
whale, again, has horny "whalebone" plates in its mouth, and no teeth;
but the young foetal whale, before it is born, has teeth in its jaws;