APPENDIX C
257
mythology
occurred when Jupiter turned himself into a bull. A construction of this nature
is not scientific, and no explanation of this kind, given of a developmental
process—embryology teems with such accounts of phenomena—will bear the
analysis of the microtome and microscope. A juggler may succeed in every
attempt to deceive his audience into the sure belief that he has converted an
old hat into a live rabbit, but the method and details of the “metamorphosis”
will not permit of a closer inspection. Surely, notwithstanding the circumstance
that writers of textbooks may state the metamorphosis of the trochophore into
the annelid as a proved fact, there is to-day no practical embryologist
prepared to maintain it ? Neither as a whole nor as to the parts of its body,
neither as an organism nor as a series of organs, does the larva, or asexual
generation, become changed into the worm, or sexual generation.
In
1886 the late Professor N. Kleinenberg set up the doctrine of “ development by
substitution of organs.” His conclusions were based on this very instance of
the developmental facts relating to the trochophore and the annelid
worm. He had found that the trochophore possessed a nervous system quite
distinct from that of the future worm, not homologous with this, and such a one
that the future central nervous system of the worm did not arise from it, but,
on the contrary, the larval one degenerated. From these and other facts, at the
close of a fine and laborious investigation, he came to the conclusion that
for any given organ—for example, the nervous system—in the course of the
ancestral history the original structure had become insufficient, and had been
replaced by a new organ arising from a different source. The old organ appeared
in the development, because the stimulus it produced was needed for the
production of the replacing organ. Applying this principle generally to all the
organs, he concluded, finally, that in development there was a substitution of
organs corresponding to that which had occurred in the history of the race.