The horns of stags are used by them in their conflicts with each other; the tusks of the elephant make this animal the most dangerous in the world, when in must. The horns of bulls, the canine teeth of many mammals, the tusks of the walrus, are further examples of organs which have been, according to Darwin, acquired through the competitions of the males with each other. The voices of mammals are used for various purposes, “as a signal of danger, as a call from one member of the troup to another, and from the mother to her lost offspring, or from the latter for protection.” “Almost all male animals use their voices much more during the rutting season than at any other time; and some, as the giraffe and porcupine, are said to be completely mute excepting at this season. As the throats (_i.e._ the larynx and thyroid bodies) of stags periodically become enlarged at the beginning of the breeding season, it might be thought that their powerful voices must be somehow of high importance to them; but this is very doubtful. From information given to me by two experienced observers, Mr. McNeill and Sir P. Egerton, it seems that young stags under three years old do not roar or bellow; and that the old ones begin bellowing at the commencement of the breeding season, at first only occasionally and moderately, whilst they restlessly wander about in search of the females. Their battles are prefaced by loud and prolonged bellowing, but during the actual conflict they are silent. Animals of all kinds which habitually use their voices utter various noises under any strong emotion, as when enraged and preparing to fight; but this may merely be the result of nervous excitement, which leads to the spasmodic contraction of almost all the muscles of the body, as when a man grinds his teeth and clenches his fists in rage or agony. No doubt stags challenge each other to mortal combat by bellowing; but those with the more powerful voices, unless at the same time the stronger, better-armed, and more courageous, would not gain any advantage over their rivals.” “Some writers suggest that the bellowing serves as a call to the female; but the experienced observers above quoted inform me that female deer do not search for the male, though the males search eagerly for the females, as indeed might be expected from what we know of the habits of other male quadrupeds. The voice of the female, on the other hand, quickly brings to her one or more stags, as is well known to the hunters who in wild countries imitate her cry.