The French naturalist _Fabre_ has described these phenomena, relying on conclusive experiments, and my own observations and those of other naturalists confirm them fully. Among the ants, all the males die also, soon after an aërial nuptial flight, in which copulation is generally polyandrous, one male hardly waiting for the preceding one to discharge his semen before taking his place. Here the female possesses a receptacle for semen which often contains the sperm of many males, and which allows it to fecundate the eggs one after another for several years as she lays them, and thus to act as the mother of an ant's nest during a period which may extend to eleven or twelve years, or even more. In the lower organisms, love consists only in sexual instinct or appetite. As soon as the function is accomplished love disappears. It is only in the higher animals that we see a more or less durable sympathy develop between the two sexes. However, here also and even in man the sexual passion intoxicates for the moment all the senses. In his sexual rut even man is dominated as by a magic influence, and for the time he sees the world only under the aspect inspired by this influence. The object loved appears to him under celestial colors, which veil all the defects and miseries of reality. Each moment of his amorous feeling inspires sentiments which it seems to him should last eternally. He swears impossible things and believes in immortal happiness. A reciprocal illusion transforms life momentarily into mirages of paradise. The most common things, and even certain things which usually disgust him, are then the object of the most violent desire. But, as soon as the orgasm is ended and the appetite satisfied the feeling of satiety appears. A curtain falls on the scene, and, at least for the moment, repose and reality reappear. Such are, in a few words, the general phenomena of the normal sexual appetite among sexual organisms in the whole of living nature. I am not speaking here of degenerations, such as onanism and prostitution. Let us now analyze this appetite further. The natural appetites are inherited instincts the roots of which lie far back in the phylogenetic history of our ancestors. Hunger forms the basis for the preservation of the individual, the sexual appetite that for the preservation of the species, as soon as reproduction takes place by separate sexes. All appetite belongs to the motor side of nervous activity; there is something internal which urges us to an act, but, on the other hand, one or more sensations may exist at the base of this something to put it in action. I have proved, for example, that the egg-laying instinct in the corpse fly (_Lucilia cæsar_) is only produced by the odor of putrefaction. As soon as the antennæ, which contain the organ of smell, are removed from these flies they cease to lay, while other more severe operations, or removal of one antenna only does not produce this result.