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