on of our modern evolution-hypothesis
is easier to explain in Virchow's case than in Von Baer's, for this
reason: morphological knowledge was greatly lacking to Virchow, while
Von Baer possessed it in the highest degree. Now morphology is
precisely that very department of inquiry in which our theory of
descent has its deepest and strongest roots, and has matured the most
glorious fruits of knowledge. The study of organic forms, or
morphology, is thus, more than any other science, interested in the
doctrine of descent, because through this doctrine it first obtained a
practical knowledge of effective causes, and was able to raise itself
from the humble rank of a descriptive study of _forms_ to the high
position of an analytical science of _form_. It is true that by the
beginning of this century the most comprehensive branch of
morphology--_i.e._, comparative anatomy--which was founded by Cuvier
and splendidly developed by Johannes Mueller, had laid the foundations
on which to build a truly philosophical science of form. The enormous
mass of various empirical material, which had been accumulated by
descriptive systematists and by the dissections of zootomists since
the time of Linnaeus and Pallas, had already been abundantly matured
and utilised in many ways for philosophic purposes by the synthetic
principles of comparative anatomy. But even the most important
universal laws of organisation--of which the old system of comparative
anatomy was one--had to take refuge in mystical ideas of a plan of
structure and of creative final causes (_causae finales_); they were
incapable of arriving at a true and clear perception of effective
mechanical causes (_causae efficientes_). This last, most difficult,
and grandest problem, Charles Darwin was the first to solve in 1859,
by setting Lamarck's theory of descent, which was already fifty years
old, on a firm footing by his own theory of selection. By this
hypothesis it was first made possible to fit together the rich
materials which had been previously amassed, into the splendid
edifice of the mechanical science of form. (See my "General
Morphology," vol. i. chap. iv.)

The immeasurable step which Darwin thus made in organic morphology can
be adequately appreciated only by those who, like myself, were brought
up in the school of the old teleological morphology, and whose eyes
were suddenly opened by the theory of selection to a comprehension of
that greatest of all biological riddl