Interest and practice in embryological research have
been remarkably stimulated during the past thirty
years by this appreciation of phylogenetic methods.
Hundreds of assiduous and able observers are now engaged
in the development of comparative embryology and its
establishment on a basis of evolution, whereas they
numbered only a few dozen not many decades ago.
It would take too long to enumerate even the most
important of the countless valuable works which have
enriched embryological literature since that time.
References to them will be found in the latest manuals
of embryology of Kolliker, Balfour, Hertwig, Kollman,
Korschelt, and Heider.
Kolliker’s Entwickelungsgeschichte des Menschen
und der hoherer Thiere, the first edition of which
appeared forty-two years ago, had the rare merit at
that time of gathering into presentable form the scattered
attainments of the science, and expounding them in
some sort of unity on the basis of the cellular theory
and the theory of germinal layers. Unfortunately,
the distinguished Wurtzburg anatomist, to whom comparative
anatomy, histology, and ontogeny owe so much, is opposed
to the theory of descent generally and to Darwinism
in particular. All the other manuals I have mentioned
take a decided stand on evolution. Francis Balfour
has carefully collected and presented with discrimination,
in his Manual of Comparative Embryology (1880), the
very scattered and extensive literature of the subject;
he has also widened the basis of the gastraea theory
by a comparative description of the rise of the organs
from the germinal layers in all the chief groups of
the animal kingdom, and has given a most thorough
empirical support to the principles I have formulated.
A comparison of his work with the excellent Text-book
of the Embryology of the Vertebrates (1890) [translation
1895] of Korschelt and Heider shows what astonishing
progress has been made in the science in the course
of ten years. I would especially recommend the
manuals of Julius Kollmann and Oscar Hertwig to those
readers who are stimulated to further study by these
chapters on human embryology. Kollmann’s
work is commendable for its clear treatment of the
subject and very fine original illustrations; its
author adheres firmly to the biogenetic law, and uses
it throughout with considerable profit. That is
not the case in Oscar Hertwig’s recent Text-book
of the Embryology of Man and the Mammals [translations
1892 and 1899] (seventh edition 1902). This able
anatomist has of late often been quoted as an opponent
of the biogenetic law, although he himself had demonstrated
its great value thirty years ago. His recent
vacillation is partly due to the timidity which our
“exact” scientists have with regard to
hypotheses; though it is impossible to make any headway
in the explanation of facts without them. However,
the purely descriptive part of embryology in Hertwig’s
Text-book is very thorough and reliable.
