some of the invertebrates. Wilhelm Roux, in particular, has made
extensive experiments, and based on them a special "mechanical
embryology," which has given rise to a good deal of discussion and
controversy. Roux has published a special journal for these subjects
since 1895, the Archiv fur Entwickelungsmechanik. The contributions to
it are very varied in value. Many of them are valuable papers on the
physiology and pathology of the embryo. Pathological experiments--the
placing of the embryo in abnormal conditions--have yielded many
interesting results; just as the physiology of the normal body has for
a long time derived assistance from the pathology of the diseased
organism. Other of these mechanical-embryological articles return to
the erroneous methods of His, and are only misleading. This must be
said of the many contributions of mechanical embryology which take up
a position of hostility to the theory of descent and its chief
embryological foundation--the biogenetic law. This law, however, when
rightly understood, is not opposed to, but is the best and most solid
support of, a sound mechanical embryology. Impartial reflection and a
due attention to paleontology and comparative anatomy should convince
these one-sided mechanicists that the facts they have discovered--and,
indeed, the whole embryological process--cannot be fully understood
without the theory of descent and the biogenetic law.


CHAPTER 1.4. THE OLDER PHYLOGENY.

The embryology of man and the animals, the history of which we have
reviewed in the last two chapters, was mainly a descriptive science
forty years ago. The earlier investigations in this province were
chiefly directed to the discovery, by careful observation, of the
wonderful facts of the embryonic development of the animal body from