owed by a
period of quiescent "encystation"; after which the contents of the cyst
escape in the form of a number of minute particles, or "spores," and
these severally develope into the parent type. Obviously this process of
conjugation, when it is thus a preliminary to multiplication, appears to
be in its essence the same as fertilization. And if it be objected that
encystation and spore-formation in the Protozoa are not always preceded
by conjugation, the answer would be that neither is oviparous
propagation in the Metazoa invariably preceded by fertilization.

Nevertheless, that there are great distinctions between true sexual
propagation and this foreshadowing of it in conjugation I do not deny.
The question, however, is whether they be so great as to justify any
argument against an historical continuity between them. What, then, are
these remaining distinctions? Briefly, as we have seen, they are the
extrusion from egg-cells of polar bodies, and the occurrence, both in
egg-cells and their products (tissue-cells), of the process of
karyokinesis. But, as regards the polar bodies, it is surely not
difficult to suppose that, whatever their significance may be, it is
probably in some way or another connected with the high specialization
of the functions which an egg-cell has to discharge. Nor is there any
difficulty in further supposing that, whatever purpose is served by
getting rid of polar bodies, the process whereby they are got rid of was
originally one of utilitarian development--i. e. a process which at its
commencement did not betoken any difference of kind, or breach of
continuity, between egg-cells and cells of simpler constitution.

Lastly, with respect to karyokinesis, although it is true that the
microscope has in comparatively recent years displayed this apparently
important distinction between unicellular and multicellular organisms,
two considerations have here to be supplied. The first is, that in some
of the Protozoa processes very much resembling those of karyokinesis
have already been observed taking place in the nucleus preparatory to
its division. And although such processes do not present quite the same
appearances as are to be met with in egg-cells, neither do the
karyokinetic processes in tissue-cells, which in their sundry kinds
exhibit great variations in this respect. Moreover, even if such were
not the case, the bare fact that nuclear division is not invariably of
the simple or direct charac