[24] Thus Kirchenoff has said (_Prorectoratsrede_, Heidelberg, 1865), “The highest object at which the natural sciences are constrained to aim is the reduction of all the phenomena of nature to mechanics;” and Helmholtz has declared (_Populaer Wissenschaft liche Vorträge_, 1869), “The aim of the natural sciences is to resolve themselves into mechanics.” Wundt observes (_Lehrbuch der Physiologie des Menschen_), “The problem of physiology is a reduction of vital phenomena to general physical laws, and ultimately to the fundamental laws of mechanics;” while Haëckel tells us (_Freie Wissenschaft und freie Lehre_) that “all natural phenomena without exception, from the motions of the celestial bodies to the growth of plants and the consciousness of men ... are ultimately to be reduced to atomic mechanics.” Evidently the last-mentioned conception was necessary to render the mechanical theory complete. As long as men believed in the action of any mysterious intelligence hidden in nature, and working through it in specific evolution towards foreseen and intended ends, a mechanical conception of nature was obviously impossible. But no less impossible was the acceptance of such a mechanical hypothesis as long as any belief remained in the existence, in individual animals, of an innate and mysterious _instinctive_ power directing their actions in ways beneficial to them or to their race, yet unintended and unforeseen by the creatures which performed those actions. A denial of the existence of any true “instinct,” as well as of any unmechanical action in specific evolution, was then necessary for the maintenance of the mechanical theory, and accordingly such denials have been confidently made, as we have already seen. While, however, this current of thought has been gaining in volume and velocity, another contrary current has no less made itself manifest, and amongst its exponents Edward Von Hartmann[25] is an eloquent advocate of the manifest action of intelligence in nature, and of what may thus be called an “intellectual” as opposed to a “mechanical” conception of the universe. He lays much stress upon instinct, and is as earnest in asserting its distinct existence and nature, as are the mechanicians in denying its existence. [25] In his work on _The Unconscious_, a translation of which has been lately published by Messrs. Trübner & Co. As was said at the beginning of the former article, the great interest just now of the study of instinct, lies in its bearings on the Darwinian hypothesis, or rather on the philosophy therewith connected. Let us then proceed to examine whether or not the analogies before pointed out between instinct and other forms of vital activity can be carried further. Let us especially examine whether the consideration of instinct in the widest sense of that term, throws any glimmerings of light upon that most recondite and still most mysterious process, _the genesis of new species_.