As far as I am aware, the only occasion on which Professor Huxley has alluded to the subject in question, is in his obituary notice of Darwin in the _Proceedings of the Royal Society_, Vol. XLIV, No. 269, p. xviii. The allusion is to my paper on _Physiological Selection_, in the _Journal of the Linnæan Society_, Zool. Vol. XIX, pp. 337-411. But it will be observed that the criticism has no reference to the theory which it is the object of that paper to set forth. It refers only to my definition of the theory of natural selection as primarily a theory of the origin, or cumulative development, of adaptations. This criticism, together with my answer thereto at the time, is conveyed in the following words. "Every variety which is selected into a species is favoured and preserved in consequence of being, in some one or more respects, better adapted to its surroundings than its rivals. In other words, every species which exists, exists in virtue of adaptation, and whatever accounts for that adaptation accounts for the existence of the species. To say that Darwin has put forward a theory of the adaptation of species, but not of their origin, is therefore to misunderstand the first principles of the theory. For, as has been pointed out, it is a necessary consequence of the theory of selection that every species must have some one or more structural or functional peculiarities, in virtue of the advantage conferred by which it has fought through the crowd of its competitors, and achieved a certain duration. In this sense, it is true that every species has been 'originated' by selection." Now, in the first place, I have nowhere said that "Darwin has put forward a theory of the adaptation of species, but not of their origin." I said, and continue to say, that he has put forward a theory of _adaptations in general_, and that where such adaptations appertain to species only (i.e. are peculiar to particular species), the theory becomes "_also_ a theory of the origin of the species which present them." The only possible misunderstanding, therefore, which can here be alleged against me is, that I fail to perceive it as a "necessary consequence of the theory of selection that _every_ species _must_ have some one or more structural or functional _peculiarities_" of an adaptive or utilitarian kind. Now, if this is a misunderstanding, I must confess to not having had it removed by Mr. Huxley's exposition.