en to the same genus. If we go still further back in time, we
discover, in the oldest rocks of all, the remains of animals, constructed
on the same general plan as the lobster, and belonging to the same great
group of _Crustacea_; but for the most part totally different from the
lobster, and indeed from any other living form of crustacean; and thus we
gain a notion of that successive change of the animal population of the
globe, in past ages, which is the most striking fact revealed by geology.

Consider, now, where our inquiries have led us. We studied our type
morphologically, when we determined its anatomy and its development, and
when comparing it, in these respects, with other animals, we made out its
place in a system of classification. If we were to examine every animal
in a similar manner, we should establish a complete body of zoological
morphology.

Again, we investigated the distribution of our type in space and in time,
and, if the like had been done with every animal, the sciences of
geographical and geological distribution would have attained their limit.

But you will observe one remarkable circumstance, that, up to this point,
the question of the life of these organisms has not come under
consideration. Morphology and distribution might be studied almost as
well, if animals and plants were a peculiar kind of crystals, and
possessed none of those functions which distinguish living beings so
remarkably. But the facts of morphology and distribution have to be
accounted for, and the science, the aim of which it is to account for
them, is Physiology.

Let us return to our lobster once more. If we watched the creature in its
native element, we should see it climbing actively the submerged rocks,
among which it delights to live, by means of its strong legs; or swimming
by powerful strokes of its great tail, the appendages of the sixth joint
of which are spread out into a broad fan-like Propeller: seize it, and it
will show you that its great claws are no mean weapons of offence;
suspend a piece of carrion among its haunts, and it will greedily devour
it, tearing and crushing the flesh by means of its multitudinous jaws.

Suppose that we had known nothing of the lobster but as an inert mass, an
organic crystal, if I may use the phrase, and that we could suddenly see
it exerting all these powers, what wonderful new ideas and new questions
would arise in our minds! The great new question would be, "How does all