_Aphis_, an egg gives rise to an imperfect female, from
which other imperfect females are born viviparously, grow, and in their
turns bear other imperfect females; and so on for eight, ten, or more
generations, until finally, perfect males and females are viviparously
produced. But now under all these, and many more, modified modes of
multiplication, the physiologist finds complete uniformity. The
starting-point, not only of every higher animal or plant, but of every
clan of organisms which by fission or gemmation have sprung from a
single organism, is always a spore, seed, or ovum. The millions of
infusoria or of aphides which, by sub-division or gemmation, have
proceeded from one individual; the countless plants which have been
successively propagated from one original plant by cuttings or tubers;
are, in common with the highest creature, primarily descended from a
fertilized germ. And in all cases--in the humblest alga as in the oak,
in the protozoon as in the mammal--this fertilized germ results from the
union of the contents of two cells. Whether, as among the lowest forms
of life, these two cells are seemingly identical in nature; or whether,
as among higher forms, they are distinguishable into sperm-cell and
germ-cell; it remains throughout true that from their combination
results the mass out of which is evolved a new organism or new series of
organisms. That this law is without exception we are not prepared to
say; for in the case of the _Aphis_ certain experiments are thought to
imply that under special conditions the descendants of an original
individual may continue multiplying for ever, without further
fecundation. But we know of no case where it _actually is_ so; for
although there are certain plants of which the seeds have never been
seen, it is more probable that our observations are in fault than that
these plants are exceptions. And until we find undoubted exceptions, the
above-stated induction must stand. Here, then, we have another of the
truths of Transcendental Physiology: a truth which, so far as we know,
_transcends_ all distinctions of genus, order, class, kingdom, and
applies to every living thing.

Yet another generalization of like universality expresses the process of
organic development. To the ordinary observer there seems no unity in
this. No obvious parallelism exists between the unfolding of a plant and
the unfolding of an animal. There is no manifest similarity between the
development