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 vegetable kingdom, which derived its support from the
absorption and conversion of inorganic matter. And so constant and
universal is this absorption, waste, and reproduction, that it may be
said with perfect certainty that there is left in no one of our bodies
at the present moment a millionth part of the matter of which they were
originally formed! We have seen, again, that not only is the living
matter derived from the inorganic world, but that the forces of that
matter are all of them correlative with and convertible into those of
inorganic nature.

This, for our present purposes, is the best view of the present
condition of organic nature which I can lay before you: it gives you
the great outlines of a vast picture, which you must fill up by your
own study.