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