The higher animals display like evidence of the same slow selective action. The courtship of the stickleback, who dances 'mad with delight' around the mate he has allured into the nest he prepares for her, has been observed by dozens of observers both before and since in the domestic aquarium. The gem-like colours of the male dragonet, the butterfly wings of certain gurnards, and the decorated tails of some exotic carps all point in the same direction. Our own larger newt is adorned during the breeding season with a serrated crest edged with orange; while in the smaller kind the colours of the body acquire at the same critical period of love-making a vivid brilliancy. The strange horns and luridly coloured throat-pouches of tropical lizards are familiar to all visitors in equatorial climates, and they are confined exclusively to the male sex. Among birds, the superior beauty of the male plumage is known to everybody; and their greatest glory invariably coincides with the special season for the selection of mates. In the spring, as even our poets have told us, the wanton lapwing gets himself another crest. The law of battle produces the spur of the game-birds and the still stranger wing-spurs of certain species of the plover kind. Æsthetic rivalry is answerable rather for vocal music, and for the plumage of the umbrella-bird, the lyre-bird, the humming-birds, and the cock of the rocks. Among mammals, strength rather than beauty seems to have carried the day; horns, and tusks, and spikes, and antlers are here the special guerdon of the victorious males. Yet even mammals show occasional signs of distinctly æsthetic and artistic preferences, as in the gracefully twisted horns of the koodoo, the scent-glands of the musk-deer or of certain antelopes, the brilliant hues of the male mandrill, and the tufts and moustaches of so many monkeys.