OCTOBER 6, 1899. ] 
ture 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 illus- 
_ trious 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 cen- 
tury Friedrich Casper Wolff 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 present 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 con- 
tinued differentiation of a primitively sim- 
ple material. It was also made clear that 
the successive changes which the embryv 
undergoes in its progress from the ovum to 
maturity are the expression of morphologic 
laws, that the progress is one from the gen- 
eral to the special, and that the shifting 
scenes of embryonic life are hints and to- 
kens of lives lived by ancestors in times 
long past. 
SCIENCE. 473: 
If we wish to measure how far off in 
biologic thought the end of the last century 
stands, not only from the end, but even 
from the middle of this one, we may imag- 
ine Darwin striving to write the ‘ Origin of 
Species’ in 1799. We may fancy him 
being told by philosophers explaining how 
one group of living beings differed from an- 
other 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 de- 
bate between the philosopher who main- 
tained that all the fossils strewn in the 
earth were the remains of animals or plants 
churned up in the turmoil of a violent uni- 
versal flood, and dropped in their places as 
the waters went away, and him who argued 
that such were not really the ‘spoils of liv- 
ing creatures,’ but the products of some 
playful plastic power which out of the su- 
perabundance 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 sur- 
roundings by any flight of genius have beat 
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 two 
great sciences of chemistry and geology 
took their birth, or at least began to stand 
alone, at the close of the last century, and 
have grown to be what we know them now 
within about a hundred years, and that the 
study of living beings has within the same 
time been so transformed as to be to-day 
something wholly different from what it was 
in 1799. And, indeed, to say more would 
