In a well-known mystic book occurs an aphorism which has become celebrated--“Love is strong as death.” The expression is not exaggerated; we may even say that love is stronger than death, since it makes us despise it. This is perhaps truer with animals than with man, and is all the more evident in proportion as the rational will is weaker, and prudential calculations furnish no check to the impetuosity of desire. For the majority of insects to love and to die are almost synonymous, and yet they make no effort to resist the amorous frenzy which urges them on. But however short may be their sexual career, one fact has been so generally observed in regard to many of them, that it may be considered as the expression of a law--_the law of coquetry_. With the greater number of species that are slightly intelligent, the female refuses at first to yield to amorous caresses. This useful practice may well have arisen from selection, for its result has invariably been to excite the desire of the male, and arouse in him latent or sleeping faculties. However brief, for example, may be the life of butterflies, their pairing is not accomplished without preliminaries; the males court the females during entire hours, and for a butterfly hours are years. We can easily imagine that the coquetry of females is more common amongst vertebrates. When the season of love arrives, many male fishes, who are then adorned with extremely brilliant colours, make the most of their transient beauty by spreading out their fins, and by executing leaps, darts, and seductive manœuvres around the females. Among fishes we begin already to observe another sexual law, at least as general as the law of coquetry, which Darwin has called the _law of battle_. The males dispute with each other for the females, and must triumph over their rivals before obtaining them. Thus, whilst the female sticklebacks are very pacific, their males are of warlike humour, and engage in furious combats in their honour. In the same way the male salmon, whose lower jaw lengthens into a crook during the breeding season, are constantly fighting amongst each other.[3] The higher we ascend in the animal kingdom the more frequent and more violent become two desires in the males--the desire of appearing beautiful, and that of driving away rivals. In South America, the males of the _Analis cristellatus_, a fissilingual saurian, have terrible battles in the breeding season, the vanquished habitually losing his tail, which is bitten off by the victor. An old observer also describes the amorous male alligator as “swollen to bursting, the head and tail raised, spinning round on the surface of the water, and appearing to assume the manner of an Indian chief relating his exploits.”[4]