APPENDIX C 259
alternation
of generations, the worm being the sexual organism or generation which succeeds
and replaces the asexual generation or larva. Although the facts—if none be
ignored or distorted—only admit of this construction, few embryologists are
supporters of it. Although direct development is no explanation whatsoever of
the facts, none the less it is still the creed—nay, the superstition— of the
majority of embryological devotees. The idea of direct development is probably
as old as the intellect of man himself. This “scientific fact “ was naturally
one of the first to arrest his attention, and even to-day can it not be
verified within the space of three weeks in any poultry-yard ? And yet it is a
superstition, and, as such, incapable of proof and impossibly true!
Underlying
the dogma of direct development is a somatic origin of germ-cells. This is not
really avoided by the assumption, made by Waldeyer and von Lenhossek, that the
fertilized egg at its first cleavage separates into two portions, one destined
to form the germ-cells, the other “the embryo.” And as little are the real
facts of the case met by Nussbaum’s aphoristic statement, which has a flavour
of some mythological account of the Creation about it “Es theilt sich das
gefurchte Ei in die somatischen und in die Geschlechtszellen.”* Should these
observers ever attempt to verify their doctrines in the actual facts of
development, even in those already recorded by the writer, they would at once
recognize how untenable their positions were. No instance is known, none is
likely to be, in which the course of events is as suggested by them.
But there
is, fortunately for the seeker after fact, one division of the higher animals
to which, while the phenomena of the life-cycle therein observed are rather
complicated, no one—at all events, nowadays—seeks to apply the doctrine of a
metamorphosis—viz., the Hydrozoa or Hydromedusae (sea-trees). Here, as Weismann
demon
* “The cleaved egg divides into the body cells
and the germ-cells.”