apid within the limited space of the mother-cell.
This is known as spore formation. The cells become detached, and do
not further develop until they have escaped from the parent. They then
increase by division and growth to form independent individuals. This
spore reproduction is found among certain types of vegetation; it also
occurs in the _protozoa_.

It is probable that these three stages of asexual reproduction are not
all the steps actually taken by Nature in the development of the early
life-process. There must have been intermediate steps, perhaps many
such, but the forms in which they occur either have not persisted, or
have not yet been studied.[11] The feature common to all ordinary
forms of asexual multiplication is that the reproductive process is
independent of sex; what starts the new life is the half, or a
liberated portion of the single parent cell. It will be readily seen
that by this process the offspring are identical with the parent. Life
continues, but it continues unchanged. Thus the power of growth is
restricted within extremely narrow limits. Any further development
required a new process. With the life-force pushing in all directions
every possible process would be tried. We are often met with striking
phenomena of adjustments to new conditions, which in some cases, when
found to be advantageous to the organism, persist. There is, in fact,
abundant evidence that Nature in these early days of life was making
experiments. In pursuance of this policy it naturally came about that
any process by which the organism gained increased power of growth had
the greater likelihood of survival. The number of devices in the way
of modification of form and habit to secure advantage is practically
infinite; but there was one principle that was eagerly seized upon at
a very early stage, and, persisting by this law of advantage, was
utilised by all progressive types as an accessory of success. This was
the principle of fertilisation, which arose in this way from what
would almost seem the chance union of two cells, at first alike, but
afterwards more and more highly differentiated, and from whose
primordial mating have proceeded by a natural series of ascending
steps all the developed forms of sex.

The ways in which this was brought about we have now to see. But even
at this point it becomes evident that the true office of sex was not
the first need of securing reproduction--that had been done
already--rather