All this is, as need hardly be said, an unsatisfying conclusion. To those permanently engaged in systematics it may well bring despair. The best course for them is once for all to recognise that whether or no specific distinction may prove hereafter to have any actual physiological meaning, it is impossible for the systematist with the means at his disposal to form a judgment of value in any given case. Their business is purely that of the cataloguer, and beyond that they cannot go. They will serve science best by giving names freely and by describing everything to which their successors may possibly want to refer, and generally by subdividing their material into as many species as they can induce any responsible society or journal to publish. Between Jordan with his 200 odd species for _Erophila_, and Grenier and Godron with one, there is no hesitation possible. Jordan's view, as he again and again declares with vehemence, is at least a view of natural facts, whereas the collective species is a mere abstraction, convenient indeed for librarians and beginners, but an insidious misrepresentation of natural truth, perhaps more than any other the source of the plausible fallacies regarding evolution that have so long obstructed progress. Nevertheless though we have been compelled to retreat from the speculative position to which scientific opinion had rashly advanced, the prospect of permanent progress is greatly better than it was. With the development of genetic research clear conceptions have at length been formed of the kind of knowledge required and of the methods by which it is to be attained. If we no longer see how varieties give rise to species, we may feel confident that a minute study of genetic physiology of varieties and species is the necessary beginning of any critical perception of their inter-relations. It is little more than a century since no valid distinction between a mechanical mixture and a chemical combination could be perceived, and in regard to the forms of life we may well be in a somewhat similar confusion. As yet the genetic behaviour of animals and plants has only been sampled. When the work has been done on a scale so large as to provide generalisations, we may be in a position to declare whether specific difference is or is not a physiological reality. FOOTNOTES: [1] Buffon, _Hist. Nat._, Oiseaux, 1780, VII, p. 3. [2] Ibid., VIII, p. 115. [3] Keeble, _Jour. Gen._, 1912, II, p. 173. [4] _Animals and Plants_, ed. 1, 1868, II, pp. 180-5. [5] _Animals and Plants_, ed. 1, 1868, II, p. 165. [6] _Species and Varieties_, 1905, p. 471. [7] Correns, _Festschr. med.-nat. Ges. zur 84 Versamml. Deutsch. Naturf. u. Aertze. Münster i. W._, 1912.