“As the case stands, the loud voice of the stag during the breeding season does not seem to be of any special service to him, either during his courtship or battles, or in any other way. But may we not believe that the frequent use of the voice, under the strong excitement of love, jealousy, and rage, continued during many generations, may at last have produced an inherited effect on the vocal organs of the stag, as well as of other male animals? This appears to me, in our present state of knowledge, the most probable view.” Here once more we find that Darwin makes use, as a sort of last resort, of the principle of the inheritance of acquired characters. As long as the theory of selection, in any of its forms, appears to offer a satisfactory solution, we find the facts used in support of this theory, but as soon as a difficulty arises the Lamarckian theory is brought to the front. It is this shifting, as we have already more than once pointed out, that shows how little real basis there is for the theory of sexual selection. The male gorilla has a tremendous voice, and he has, as has also the orang, a laryngeal sac. One species of gibbon has the power of producing a correct octave of musical notes. “The vocal organs of the American _Mycetes caraya_ are one-third larger in the male than in the female, and are wonderfully powerful. These monkeys in warm weather make the forests resound at morning and evening with their overwhelming voices. The males begin the dreadful concert, and often continue it during many hours, the females sometimes joining in with their less powerful voices. An excellent observer, Rengger, could not perceive that they were excited to begin by any special cause; he thinks that, like many birds, they delight in their own music, and try to excel each other. Whether most of the foregoing monkeys have acquired their powerful voices in order to beat their rivals and charm the females—or whether the vocal organs have been strengthened and enlarged through the inherited effects of long-continued use without any particular good being thus gained—I will not pretend to say; but the former view, at least in the case of the _Hylobates agilis_, seems the most probable.” The odor of some mammals is confined to, or more developed, in the males; but in some forms, as in the skunk, it is present in both sexes. In the shrew mice, abdominal scent glands are present, but since these mice are rejected by birds of prey, their glands probably serve to protect them; “nevertheless the glands become enlarged in the males during the breeding season.” In many other quadrupeds the scent glands are of the same size in both sexes, and their function is unknown.