In relation to the Sexual Selection theory these excrescences are of quite exceptional interest, for they throw a strong light on the meaning of ornament, such as obtains among birds, which seem to show a consciousness of its existence and effectiveness. Darwin argued from the birds to the Beetles. Convinced that the gorgeous crests and trains and vivid colours were appreciated by the females of the former, he was impelled to believe that the ornaments of the latter had developed in like case by the fostering influences of the females. Similarly, from the evidence as to the use of horns in the case of mammals, and spurs in the case of birds, he was induced to believe that the horn-like outgrowths of Beetles had been attained by like influences. But in both kinds of cases, he could only infer their action, for he could discover no really decisive instances of conquest either by display or by battle, such as he was able to produce in the case of the higher animals. Had chance directed his attention in the beginning either to the Warblers among the birds, or the beetles among the insects, his interpretation of the action of sexual selection, it is more than probable, would have been materially different from that developed in the “Descent of Man.” No additions of any importance have been added to the facts he so laboriously collected. As touching the “horns” it should be remarked that these may arise either from the head or from the thorax, or from both, and sometimes even from the under surface of the body. One of the most remarkable instances of these singular outgrowths is that of the Hercules Beetle (_Dynastes hercules_) of the West Indies and tropical America. Herein the roof of the head is prolonged into a great upturned beam bearing tooth-like prominences, and the top of this is opposed to a still more massive beam, whose base covers the whole roof of the thorax, and whose tip extends far beyond that projecting from the head. A pair of “teeth” point downwards from the middle of this beam, whose under surface is thickly covered with short chestnut-coloured hairs forming a brush-like surface. In another, _Copris isidis_, the head bears two short, rhinoceros-like horns, and the thorax a short, triangular overhanging ledge: in _Phanœus jaunus_ there is a single horn on the head, and the thorax bears two short, forwardly-projecting blades, one on each side; while in _Onthophagus rangifer_—the Reindeer Beetle—the head bears a pair of horns curiously like the antlers of a deer. One might cite many such instances, all varying in detail, but these will suffice.