organization" of the animal kingdom which has been guessed at and
fancied for many years; but which it has been left to the present time
to be demonstrated by the careful study of development. But is it
possible to go another step further still, and to show that in the same
way the whole of the organic world is reducible to one primitive
condition of form? Is there among the plants the same primitive form of
organization, and is that identical with that of the animal kingdom? The
reply to that question, too, is not uncertain or doubtful. It is now
proved that every plant begins its existence under the same form; that
is to say, in that of a cell--a particle of nitrogenous matter having
substantially the same conditions. So that if you trace back the oak to
its first germ, or a man, or a horse, or lobster, or oyster, or any
other animal you choose to name, you shall find each and all of these
commencing their existence in forms essentially similar to each other:
and, furthermore, that the first processes of growth, and many of the
subsequent modifications, are essentially the same in principle in
almost all.

In conclusion, let me, in a few words, recapitulate the positions which
I have laid down. And you must understand that I have not been talking
mere theory; I have been speaking of matters which are as plainly
demonstrable as the commonest propositions of Euclid--of facts that must
form the basis of all speculations and beliefs in Biological science. We
have gradually traced down all organic forms, or, in other words, we
have analyzed the present condition of animated nature, until we found
that each species took its origin in a form similar to that under which
all the others commence their existence. We have found the whole of the
vast array of living forms, with which we are surrounded, constantly
growing, increasing, decaying and disappearing; the animal constantly
attracting, modifying, and applying to its sustenance the matter of the