xcept that their skin had a curious bluish
tinge not now to be seen.

But surprising as were the changes in the size, consistency, and
appearance of man's body during this period, the alterations in the
process of reproduction are still more astounding. A reference to the
systems which now obtain among the lower kingdoms of nature may help
us in the consideration of the subject.

[Sidenote: Processes of Reproduction.]

After instancing the simplest processes of propagation by self-division,
and by the formation of buds (Gemmatio), Haeckel proceeds, "A third mode
of non-sexual propagation, that of the formation of germ-buds
(Polysporogonia) is intimately connected with the formation of buds. In
the case of the lower, imperfect organisms, among animals, especially in
the case of the plant-like animals and worms, we very frequently find
that in the interior of an individual composed of many cells, a small
group of cells separates itself from those surrounding it, and that this
small isolated group gradually develops itself into an individual, which
becomes like the parent and sooner or later comes out of it.... The
formation of germ buds is evidently but little different from real
budding. But, on the other hand, it is connected with a fourth kind of
non-sexual propagation, which almost forms a transition to sexual
reproduction, namely, the formation of germ cells (Monosporogonia). In
this case it is no longer a group of cells but a single cell, which
separates itself from the surrounding cells in the interior of the
producing organism, and which becomes further developed after it has
come out of its parent.... Sexual or amphigonic propagation
(Amphigonia) is the usual method of propagation among all higher animals
and plants. It is evident that it has only developed at a very late
period of the earth's history, from non-sexual propagation, and
apparently in the first instance from the method of propagation by
germ-cells.... In all the chief forms of non-sexual propagation
mentioned above--in fission, in the formation of buds, germ-buds, and
germ-cells--the separated cell or group of cells was able by itself to
develop into a new individual, but in the case of sexual propagation,
the cell must first be fructified by another generative substance. The
fructifying sperm must first mix with the germ-cell (the egg) before the
latter can develop into a new individual. These two generative
substances, the sperm and the egg, ar