Any other mode of interference by a directive teleological power in the processes of the universe than by the appointment of the forces producing them, is however, at least to the naturalist, inadmissible. We are still far removed from completely understanding the mechanism by means of which the organic world is evoked--we still find ourselves at the very beginning of knowledge. We are, however, already convinced that both the organic and the inorganic worlds are dependent only upon mechanical forces, for to this conclusion we are led, not only by the results of investigators who have restricted themselves to limited provinces, but also by the most general considerations. But although the force of these arguments may not be acknowledged, and although one might maintain that the inductional proofs against the existence of a “phyletic vital force” have been directed only against points of detail, or have never been completely demonstrated, _i.e._ for all points, it must nevertheless be conceded, that for the naturalist the mechanical conception of Nature is the only one possible--that he is not at all justified in abandoning this view so long as the interference of teleological forces _in the course_ of the processes of organic development has not been demonstrated to him. Thus, it will not be immaterial whether a conception of Nature which to many seems inevitable is consistent with the idea of universal design, or a final directive universal principle, since the value which we may attach to our own lives and aims, essentially depends thereon. The final and main result of this essay will thus be found in the attempted demonstration that the mechanical conception of Nature very well admits of being united with a teleological conception of the Universe. THE END. FOOTNOTES [171] [The slight variability in the colour of this pupa, opens up the interesting question of the photographic sensitiveness of this and other species, which is stated to cause them to assimilate in colour to the surface on which the larva undergoes its final ecdysis. Some experiments upon this subject have been recorded by Mr. T. W. Wood, Proc. Ent. Soc. 1867, p. xcix, but the field is still almost unexplored. R.M.] [172] “Über den Einfluss der Isolirung auf die Artbildung.” Leipzig, 1872, p. 20. [173] In some instances _Deilephila Lineata_ has also been seen by day hovering over flowers. [174] It is true that I only reared one brood, but from this fifty specimens were obtained. It would be interesting to know whether this variety of the caterpillar is distributed over the whole of Southern Europe.