ff, and, later on, others, had
strenuously opposed such a view, it held its own, not only to the close of
the century, but far on into the next. It was not until a quarter of the
nineteenth century had been added to the past that Von Baer made known the
results of researches which once and for all swept away the old view. He
and others working after him made it clear that each individual puts on
its final form and structure, not by an unfolding of preexisting hidden
features, but by the formation of new parts through the continued
differentiation of a primitively simple material. It was also made clear
that the successive changes which the embryo undergoes in its progress
from the ovum to maturity are the expression of morphologic laws; that the
progress is one from the general to the special; and that the shifting
scenes of embryonic life are hints and tokens of lives lived by ancestors
in times long past.

If we wish to measure how far off in biologic thought the end of the
eighteenth century stands, not only from the end, but even from the middle
of the nineteenth, we may imagine Darwin striving to write the "Origin of
Species" in 1799. We may fancy his being told by philosophers how one
group of living beings differed from another group because all its members
and all their ancestors came into existence at one stroke, when the
first-born progenitor of the race, within which all the rest were folded
up, stood forth as the result of a creative act. We may fancy him
listening to a debate between the philosopher who maintained that all the
fossils strewn in the earth were the remains of animals or plants churned
up in the turmoil of a violent universal flood, and dropped in their
places as the waters went away, and him who argued that such were not
really the "spoils of living creatures," but the products of some playful
plastic power which, out of the superabundance of its energy, fashioned
here and there the lifeless earth into forms which imitated, but only
imitated, those of living things. Could he amid such surroundings, by any
flight of genius, have beaten his way to the conception for which his name
will ever be known?

* * * * *

Here I may well turn away from the past. It is not my purpose, nor, as I
have said, am I fitted, nor is this perhaps the place, to tell even in
outline the tale of the work of science in the nineteenth century. I am
content to have pointed out that the t