Here, then, we have actual proof of “hereditary individual variations” among a-sexually propagating organisms, sufficient in amount to have given origin, not merely to “individual differences,” but to innumerable species, and even genera. Consequently Weismann allows that the criticism abolishes this line of evidence in favour of the absolute stability of germ-plasm[26]. Consquently, also, we must now add, in whatever measure the alleged fact would have corroborated the theory had it been proved to be a fact, in that measure is the theory discredited by proof that it is not a fact. For, if the theory were sound, this particular fact would certainly have admitted of demonstration: therefore the proof that it is not a fact—but the reverse of a fact—amounts at the same time to a disproof of the theory[27]. The only other line of evidence to be adduced in favour of the absolute stability of germ-plasm is that which is furnished by the high antiquity of some specific types, by the facts of atavism, and by the persistency of vestigial organs. But this line of evidence is as futile as the other. Nobody has ever questioned that hereditary characters are persistently stable as long as they are persistently maintained by natural selection; and this, according to Weismann himself, must have been the case with all long-enduring species: these, therefore, fail to furnish any evidence of the _inherent_ stability of germ-plasm, which is the only point in question. Again, as regards the facts of atavism, nobody is disputing these facts. What we are disputing is whether the _degree_ of inherent stability which they unquestionably prove can be rationally regarded as such that it may endure, not merely for such a comparatively small number of generations as these facts imply, but actually for any number of generations, or through the practically infinite series of generations that now intervene between the higher metazoa and their primeval parentage in the protozoa. Clearly, the ratio between these two things is such that no argument derived from the facts of atavism can be of any avail for the purposes of this Weismannian doctrine. Lastly, as regards vestigial organs, the consideration that, surprisingly persistent as they unquestionably are, nevertheless they do eventually disappear, seems to prove that the power of heredity does in time become exhausted, even in cases most favourable to its continuance. That it should thus become finally exhausted is no more than Darwin’s theory of perishable gemmules, or Galton’s theory of a not absolutely stable stirp, would expect. But the fact is irreconcilable with Weismann’s theory of an absolutely stable germ-plasm.