Regarding the cessation of selection, the motive that prompted my question to you was not the paltry one of claiming priority in the enunciation of an exceedingly obvious idea. My motive was to assure myself that this idea is exactly the same as Weismann's Panmixia; for, although I could see no difference, I thought perhaps he and you did (from absence of allusion to my paper, while priority is acknowledged as regards a later one); and, if this were so, I wanted to know where the difference lay. And the reason I wanted to know this was because when my paper was published, and Darwin accepted the idea with enthusiasm, I put it to him in conversation whether this idea might not supersede Lamarckian principles altogether. (By carefully reading between the lines of the paper itself, you will see how much this question was occupying my mind at the time, though I did not dare to challenge Lamarck's principles _in toto_ without much more full inquiry.) Then it was that Darwin dissuaded me from going on to this point, on the ground that there was abundant evidence of Lamarck's principles apart from use and disuse of structures--_e.g._ instincts--and also on the ground of his theory of Pangenesis. Therefore I abandoned the matter, and still retain what may thus be now a prejudice against exactly the same line of thought as Darwin talked me out of in 1873. Weismann, of course, has greatly elaborated this line of thought; but what may be called the scientific axis of it (viz. possible non-inheritance of acquired characters) is identical, and all the more metaphysical part of it about the immortality, immutability, &c., of a hypothetical germ-plasm is the weakest part in my estimation. Now, the point I am working up to is this. If there be no difference between Panmixia and Cessation of Selection, from what I have briefly sketched about it, it follows that, had Darwin lived till now, he would almost certainly have been opposed to Weismann. This is not a thing I should like to say in public, but one that I should like to feel practically assured about in my own mind. Regarding the numerical calculations, I have not got a copy of the 'Nature' paper here, but, so far as I remember (and I think I am right), the idea was that 'Economy of Growth' would go on assisting Cessation of Selection till the degenerating organ became 'rudimentary.' In other words, _reversal_ of selection would co-operate with _cessation_ of it.