You will see what I mean by 'secondary variations' by looking at page 366 of my paper. It is merely a short-hand expression for all other specific differences save the sexual difference of sterility. My view is that these secondary differences are always sure to arise sooner or later in some direction or another wherever a portion of a species is separated from the rest, whether by geographical or physiological isolation, which, indeed, as regards the former, is no more than you (following Weismann, &c.) acknowledge. Now, to me it seems obvious that Weismann's 'variations' (_i.e._ slight changes in the form of shells) cannot possibly be themselves my 'physiological sports,' although they may very well be the consequences of such a sport leading to physiological isolation, and so to independent variation in two or three directions simultaneously, till afterwards blended by intercrossing. And my reason for thinking this is that 'Weismann's variations' always arose in crops at enormously long intervals of time. On the mere doctrine of chances it therefore becomes impossible to suppose that each of these variations was due to a separate physiological sport, although it is easy to see how each crop of them might have been so. For, if not, why should they always have arisen in crops, each member of which was demonstrably fertile with the other members of that crop, while no less demonstrably sterile with the original parent form? Therefore, what I see in these facts is precisely what, upon my theory, I should expect to see, viz. first, a 'primary variation,' or 'physiological sport,' arising at long intervals; secondly, closely following upon this, a crop of 'secondary variations' in the way of slight morphological changes affecting two or three different 'strains' simultaneously; and thirdly, an eventual blending of these strains by intercrossing with one another without being able to intercross with the surrounding and (at first) very much more numerous parent form. But I can now quite understand why you thought these facts were 'dead against' me; you thought that every single slight change of morphology must (on my theory) have had a separate 'physiological sport' to account for it. This, however, most emphatically is not my theory. Physiological isolation I regard as having morphological consequences precisely analogous to those of geographical isolation; and you would not think of arguing that there must be a separate geographical isolation for every slight change of structure--for example, that a peculiar species of plant growing on a mountain top must have had one isolation to explain its change of form, and another isolation to explain its change of colour.