enclosed in the
minutest possible form within the egg, and is thus included in the
parental organism, in miniature indeed, but quite complete. Thus the
problem of the "development of form" or of "heredity" was, so to speak,
ruled out of court; all that was assumed was continuous growth and
self-unfolding.

Opposed to this theory was one of later growth, the theory of epigenesis,
which maintained that the organism developed without preformation from the
still undifferentiated and homogeneous substance of the egg. The
supporters of the first theory considered themselves much more scientific
and exact than those of the second. And not without reason. For the theory
of epigenesis obviously required mysterious formative principles, and
equally mysterious powers of recollection and recapitulation, which
impelled the undifferentiated ovum substance into the final form,
precisely like that of its ancestors. Nor need the preformationists have
greatly feared the reproach, that the parental organism must have been
included within the grand-parental, and so on backwards to the first
parents in Paradise. For this "Chinese box" encapsulement theory only
requires that we should grant the idea of the infinitely little, and that
idea is already an integral part of our thinking.

Modern biologists ridicule the preformation hypothesis as altogether too
artificial. And undoubtedly it founders on the facts of embryology, which
disclose nothing to suggest the unfolding of a pre-existent miniature
model, but show us how the egg-cell divides into two, into four, and so
on, with continued multiplication followed by varied arrangements and
rearrangements of cells--in short, all the complex changes which constitute
development. But a preformation in some sense or other there must be;--some
peculiar material predisposition of the germ, which, as such, supplies the
directing principle for the development, and the sufficient reason for the
repetition of the parental form. This is of such obvious importance from
the mechanical point of view that the speculations of to-day tend to move
along the old preformationist lines. To these modern preformationists are
opposed the modern upholders of epigenesis or gradual differentiation, who
attempt to elaborate a mechanical theory of development. And with the
contrast between these two schools there is necessarily associated the
discussion as to the inheritance or non-inheritance of acquired
characters.

D