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.
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