optical analysis at our command, assert with confidence that in structure,
using that word in its ordinary sense, it is in all cases absolutely
simple. It is equally well known that the features of form which supply
the characters of a grown-up living being, all the many and varied
features of even the most complex organism, are reached as the goal of a
road, at times a long road, of successive changes; that the life of every
being, from the ovum to its full estate, is a series of shifting scenes,
which come and go, sometimes changing abruptly, sometimes melting the one
into the other, like dissolving views--all so ordained that often the
final shape with which the creature seems to begin, or is said to begin,
its life in the world is the outcome of many shapes, clothed with which it
in turn has lived many lives before its seeming birth.

All, or nearly all, the exact knowledge of the labored way in which each
living creature puts on its proper shape and structure is the heritage of
the present century. Although the way in which the chick is moulded in the
egg was not wholly unknown even to the ancients, and in later years had
been told, first in the sixteenth century by Fabricius, then in the
seventeenth century, in a more clear and striking manner, by the great
Italian naturalist, Malpighi, the teaching thus offered had been neglected
or misinterpreted. At the close of the eighteenth century the dominant
view was that in the making of a creature out of the egg there was no
putting on of wholly new parts, no epigenesis. It was taught that the
entire creature lay hidden in the egg, hidden by reason of the very
transparency of its substance; lay ready-made, but folded up, as it were;
and that the process of development within the egg or within the womb was
a mere unfolding, a simple evolution. Nor did men shrink from accepting
the logical outcome of such a view--namely, that within the unborn
creature itself lay in like manner, hidden and folded up, its offspring
also, and within that, again, its offspring in turn, after the fashion of
a cluster of ivory balls carved by Chinese hands, one within the other.

This was no fantastic view, put forward by an imaginative dreamer; it was
seriously held by sober men, even by men like the illustrious Haller, in
spite of their recognizing that, as the chick grew in the egg, some
changes of form took place. Though so early as the middle of the
eighteenth century Friedrich Casper Wol