One of the most formidable of the opponents of the Sexual Selection theory was Wallace. But his arguments were far from convincing, and often inconsistent. He attributed the more frequent occurrence in male animals of brilliant coloration and exaggerations of growth such as give rise to manes, beards, long plumes, and so on, to a “surplus of strength, vitality and growth-power which is able to expend itself in this way without injury,” or, as he sometimes expresses it, to superabundant vitality. He was evidently striving to find words for the faith that was in him, and he was nearer the truth than he knew or than his critics supposed. He was seeking facts which only the physiologist could furnish. And these made their appearance long years after with Professor Starling’s discovery of Hormones. We are far from understanding the origin of these mysterious juices which must be so frequently alluded to in these pages, but they are evidently intimately associated with the expenditure of energy. This may sometimes find an outlet in increased stature, sometimes in pure luxuries of growth. The force of Wallace’s arguments was crushed out by the weight of detail they were made to bear. Mr. J. T. Cunningham a few years ago entered the lists and failed to achieve his purpose no less completely. His was a theory which assumed too much. In the first place it was based on the transmissibility of acquired characters, of the truth of which there is at present no evidence. He contends, for example, that the vivid hues of scarlet, blue, yellow and violet which colour the naked skin of the neck of the cassowaries and of both sexes, and the curious horny casque which surmounts the head, are the outcome of the constant laceration of the skin inflicted by the males during their conflicts for the possession of the females. He assumes that such conflicts take place, and he assumes that such “acquired characters” are transmitted. Now, as a matter of fact, these birds do not fight with their beaks, but with their feet. And to this end the claw of the inner toe is enlarged to form a great spur. But there is no evidence that the skin of the neck is ever damaged in such conflicts as they may engage in. No scars are ever found, at any rate, to lend support to this theory. The casque, which is similarly supposed to be a mark of honourable conflict, is an “ornament” of great frailty, for it is composed of a delicate filigree-work of bone covered with a thin sheath of horn. In like manner, the long plumes which surmount the heads of birds like the Peacock, and many Birds of Paradise, and the wattle which surmounts the beak of the Turkey, are supposed to have had their origin in similar pugilistic encounters in the past. Mr. Cunningham is surely pushing the theory of the transmission of acquired characters a little far. For what has been transmitted in these cases is not a number of scarred surfaces, but a series of hypertrophied structures.