The time has now come to prove, by means of quotations, that I have from the first represented the "principle," or "essence," of physiological selection to consist in selective fertility furnishing a needful condition to specific differentiation, in at least a large proportional number of allied species which afterwards present the reciprocal character of cross-sterility; that I have never represented variations in the way of this selective fertility as necessarily constituting the initial variations, or as always arising "alone, in an otherwise undifferentiated species"; and that, although I have uniformly given it as my opinion that these variations do _in some cases_ thus arise (especially among plants and lower invertebrata), I have as uniformly stated "that it makes no difference to the theory in what proportional number of cases they have done so"--or even if, as Mr. Wallace supposes, they have never done so in any case at all[59]. These statements (all of which are contradictory of the only points of difference alleged) have already been published in my article in the _Monist_ of October, 1890. And although Mr. Wallace, in his reply to that article, ignores my references to the "original paper," it is scarcely necessary to quote the actual words of the paper itself, since the reader who is further interested in this controversy can readily refer to it in the _Journal of the Linnaean Society_ (vol. xix. pp. 337-411). [59] This refers to what I understand Mr. Wallace to say in the _Nature_ correspondence is the supposition on which his own theory of the origin of species by cross-infertility is founded. But in the original statement of that theory itself, it is everywhere "supposed" that when species are originated by cross-infertility, the _initial_ change _is_ the physiological change. In his original statement of that theory, therefore, he literally went further than I had gone in my "original paper," with reference to supposing the physiological change to be the initial change. I do not doubt that this is due to some oversight of expression; but it is curious that, having made it, he should still continue his endeavour to fix exactly the same oversight upon me.