The Perpetuation of Living Beings, Hereditary Transmission and Variation | Page 4

mutual action and interaction of certain
portions of the organisms of usually two distinct individuals,--the male
and the female. The cases of asexual perpetuation are by no means so
common as the cases of sexual perpetuation; and they are by no means
so common in the animal as in the vegetable world. You are all
probably familiar with the fact, as a matter of experience, that you can
propagate plants by means of what are called "cuttings;" for example,
that by taking a cutting from a geranium plant, and rearing it properly,
by supplying it with light and warmth and nourishment from the earth,
it grows up and takes the form of its parent, having all the properties
and peculiarities of the original plant.
Sometimes this process, which the gardener performs artificially, takes
place naturally; that is to say, a little bulb, or portion of the plant,
detaches itself, drops off, and becomes capable of growing as a separate
thing. That is the case with many bulbous plants, which throw off in
this way secondary bulbs, which are lodged in the ground and become
developed into plants. This is an asexual process, and from it results the
repetition or reproduction of the form of the original being from which
the bulb proceeds.
Among animals the same thing takes place. Among the lower forms of
animal life, the infusorial animalculae we have already spoken of throw
off certain portions, or break themselves up in various directions,
sometimes transversely or sometimes longitudinally; or they may give
off buds, which detach themselves and develop into their proper forms.
There is the common fresh-water Polype, for instance, which multiplies
itself in this way. Just in the same way as the gardener is able to
multiply and reproduce the peculiarities and characters of particular
plants by means of cuttings, so can the physiological
experimentalist--as was shown by the Abbe Trembley many years
ago--so can he do the same thing with many of the lower forms of
animal life. M. de Trembley showed that you could take a polype and

cut it into two, or four, or many pieces, mutilating it in all directions,
and the pieces would still grow up and reproduce completely the
original form of the animal. These are all cases of asexual
multiplication, and there are other instances, and still more
extraordinary ones, in which this process takes place naturally, in a
more hidden, a more recondite kind of way. You are all of you familiar
with those little green insects, the 'Aphis' or blight, as it is called. These
little animals, during a very considerable part of their existence,
multiply themselves by means of a kind of internal budding, the buds
being developed into essentially asexual animals, which are neither
male nor female; they become converted into young 'Aphides', which
repeat the process, and their offspring after them, and so on again; you
may go on for nine or ten, or even twenty or more successions; and
there is no very good reason to say how soon it might terminate, or how
long it might not go on if the proper conditions of warmth and
nourishment were kept up.
Sexual reproduction is quite a distinct matter. Here, in all these cases,
what is required is the detachment of two portions of the 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