Could the future not complete a work the design of which is so very clearly traced? We ask ourselves this the more readily inasmuch as every appearance encourages the question. Examine under the magnifying-glass the frontal horns of Onthophagus Taurus in the pupa state; then consider as carefully the spear upon the corselet. At first, there is no difference between them, except the general configuration. In both cases, we find the same glassy aspect, the same sheath swollen with a crystalline moisture, the same incipient organ plainly marked. A leg in formation is not more clearly declared than the horn on the corselet or those on the forehead. Can time be lacking for the thoracic growth to organize itself into a stiff and lasting appendage? The evolution of the nymph is swift; the insect is perfect in a few weeks. Could it not be that, though this brief space suffice to promote the maturity of the horns on the forehead, the thoracic horn requires a longer time to ripen? Let us prolong the nymphal period artificially and give the germ time to develop itself. It seems to me that a decrease of temperature, moderated and maintained for some weeks, for months if necessary, should be capable of bringing about this result, by delaying the progress of the evolution. Then, with a gentle slowness, favourable to delicate formations, the promised organ will crystallize, so to speak, and become the spear heralded by appearances. The experiment attracted me. I was unable to undertake it for lack of the means whereby to produce a cold, even and lasting temperature. What should I have obtained if my penury had not made me abandon the enterprise? A retarding of the progress of the metamorphosis, but nothing more, apparently. The horn on the corselet would have persisted in its sterility and, sooner or later, would have disappeared. I have reasons for my conviction. The abode of the Onthophagus while engaged on his metamorphosis is not deep down; variations of temperature are easily felt. On the other hand, the seasons are capricious, especially the spring. Under the skies of Provence, the months of May and June, if the mistral lend a hand, have periods when the thermometer drops in such a way as to suggest a return of winter. To these vicissitudes let us add the influence of a more northerly climate. The Onthophagi occupy a wide zone of latitude. Those of the north, less favoured by the sun than those of the south, can, if changing circumstances assist at the time of the transformation, undergo long weeks of a decreased temperature which spins out the work of evolution and ought therefore to permit the thoracic armour, at long intervals and casually, to consolidate into a horn. Here and there, then, the conditions of a moderate, or even cold temperature, at the time of the nymphosis, are realized without the aid of my artifices.