parental organisms, which portions we know as the egg and the
spermatozoon. In plants it is the ovule and the pollen-grain, as in the
flowering plants, or the ovule and the antherozooid, as in the
flowerless. Among all forms of animal life, the spermatozoa proceed
from the male sex, and the egg is the product of the female. Now, what
is remarkable about this mode of reproduction is this, that the egg by
itself, or the spermatozoa by themselves, are unable to assume the
parental form; but if they be brought into contact with one another,
the effect of the mixture of organic substances proceeding from two
sources appears to confer an altogether new vigour to the mixed product.
This process is brought about, as we all know, by the sexual
intercourse of the two sexes, and is called the act of impregnation.
The result of this act on the part of the male and female is, that the
formation of a new being is set up in the ovule or egg; this ovule or
egg soon begins to be divided and subdivided, and to be fashioned into
various complex organisms, and eventually to develop into the form of
one of its parents, as I explained in the first lecture. These are the
processes by which the perpetuation of organic beings is secured. Why
there should be the two modes--why this re-invigoration should be
required on the part of the female element we do not know; but it is
most assuredly the fact, and it is presumable, that, however long the
process of asexual multiplication could be continued, I say there is
good reason to believe that it would come to an end if a new
commencement were not obtained by a conjunction of the two sexual
elements.

That character which is common to these two distinct processes is this,
that, whether we consider the reproduction, or perpetuation, or
modification of organic beings as they take place asexually, or as they
may take place sexually,--in either case, I say, the offspring has a