nert, it is
inadmissible to connect birds with a definite class of reptiles.
Haeckel finds his way out of the difficulty by supplying hypothetical
forms which no one has ever seen, but which his imagination has
admirably depicted as transitional forms. In so doing, however, he
abandons the inductive method of natural science.

It is impossible for us to treat at such length all the remaining
sections of this important book. We may mention in passing that
Fleischmann examines the "roots of the mammal stock," and enters upon a
detailed discussion of "the origin of lung-breathing vertebrates," the
"real phylo-genetic problem of the mollusks," and "the origin of the
echinodermata." It is evident that he boldly takes up the most
important problems connected with the theory of Descent, and does not
confine himself to a one-sided discussion of individual points. As he
did not fear to examine thoroughly the famous, and as it hitherto
appeared, invulnerable, "parade-horse," so neither does he hesitate to
demolish the other reputed proof for the doctrine of Descent, e.g., the
fresh-water snail of Steinheim, the remains of which Hilzendorf and
Neumayr examined and were said to have arranged in lines of descent
that "would actually stagger one." It is important to call especial
attention to this because the adversaries of the book ignore it. He
next shows up the so-called "fundamental principle of biogenesis"
according to which organisms are supposed to repeat during their
individual development the forms of their progenitors (enunciated by
Fritz Mueller and Haeckel). Fleischmann points out the exceptions which
Haeckel attributes to "Cenogenesis," (that is to falsification) and
shows the disagreement among contemporary naturalists regarding this
fundamental principle. Even Haeckel's friend and pupil, O. Hertwig
sounds the retreat.

The 15th chapter deals with the "Collapse of Haeckel's Doctrine," which
is revealed in the fact that "the practical possibility of ascertaining
anything regarding the primitive history of the animal kingdom is
completely exhausted and the hope of so doing forever frustrated."
"Instead of scientists having been able from year to year to produce an
increasing abundance of proof for the correctness of the doctrine of
Descent, the lack of proofs and the impossibility of procuring evidence
is to-day notorious." In the last chapter Fleischmann finally attempts
to prove on logical principles the untenableness