quainted with, it is really an egg.
After a time this minute particle of matter, which may only be a
small fraction of a grain in weight, undergoes a series of
changes,--wonderful, complex changes. Finally, upon its surface there
is fashioned a little elevation, which afterwards becomes divided and
marked by a groove. The lateral boundaries of the groove extend upwards
and downwards, and at length give rise to a double tube. In the upper
smaller tube the spinal marrow and brain are fashioned; in the lower,
the alimentary canal and heart; and at length two pairs of buds shoot
out at the sides of the body, which are the rudiments of the limbs. In
fact a true drawing of a section of the embryo in this state would in
all essential respects resemble that diagram of a horse reduced to its
simplest expression, which I first placed before you (Fig. 1).

Slowly and gradually these changes take place. The whole of the body,
at first, can be broken up into "cells," which become in one place
metamorphosed into muscle,--in another place into gristle and bone,--in
another place into fibrous tissue,--and in another into hair; every part
becoming gradually and slowly fashioned, as if there were an artificer
at work in each of these complex structures that we have mentioned. This
embryo, as it is called, then passes into other conditions. I should
tell you that there is a time when the embryos of neither dog, nor
horse, nor porpoise, nor monkey, nor man, can be distinguished by any
essential feature one from the other; there is a time when they each and
all of them resemble this one of the Dog. But as development advances,
all the parts acquire their speciality, till at length you have the
embryo converted into the form of the parent from which it started. So
that you see, this living animal, this horse, begins its existence as
a minute particle of nitrogenous matter, which, being supplied with
nutriment (derived, as I have shown, from the inorganic world), grows up
according to the special type and construction of its parents, works
and undergoes a constant waste, and that waste is made good by nutriment
derived from the inorganic world; the waste given off in this way being
directly added to the inorganic world; and eventually the animal itself
dies, and, by the process of decomposition, its whole body is returned
to those conditions of inorganic matter in which its substance
originated.

This, then, is that which is true of every li