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.”