Now, if we are all agreed so far, the only question that remains is whether or not this criterion of Heredity is capable of supplying a basis for the generalization, that all characters which have been ranked as of specific value must necessarily be regarded as presenting also an adaptive, or life-serving, value? I will now endeavour to show that there are certain very good reasons for answering this question in the negative. (A.) In the first place, even if the modifications induced by the direct action of a changed environment are not hereditary, who is to know that they are not? Assuredly not the botanist or zoologist who in a particular area finds what he is fully entitled to regard as a well-marked specific type. Only by experiments in transposition could it be proved that the modifications have been produced by local conditions; and although the researches of many experimentalists have shown how considerable and how constant such modifications may be, where is the systematic botanist who would ever think of transplanting an apparently new species from one distant area to another before he concludes that it is a new species? Or where is the systematic zoologist who would take the trouble to transport what appears to be an obviously endemic species of animal from one country to another before venturing to give it a new specific name? No doubt, both in the case of plants and animals, it is tacitly assumed that constant differences, if sufficient in amount to be regarded as specific differences are hereditary; but there is not one case in a hundred where the validity of this assumption has ever been tested by experiments in transposition. Therefore naturalists are apt to regard it as remarkable when the few experiments which have been made in this direction are found to negative their assumption--for example, that a diagnostic character in species of the genus _Hieratium_ is found by transplantation not to be hereditary, or that the several named species of British trout are similarly proved to be all "local varieties" of one another. But, in point of fact, there ought to be nothing to surprise us in such results--unless, indeed, it is the unwarrantable nature of the assumption that any given differences of size, form, colour, &c., which naturalists may have regarded as of specific value, are, on this account, hereditary. Indeed, so surprising is this assumption in the face of what we know touching both the extent and the constancy of climatic variation, that it seems to me such a naturalist as Kerner, who never considers the criterion of heredity at all, is less assailable than those who profess to constitute this their chief criterion of specific distinction. For it is certain that whatever their professions may have nowadays become, systematic naturalists have never been in the habit of really following this criterion. In theory they have of late years attached more and more weight to definition No.