If we look at nature we see everywhere the same desire and the same attraction of the sexes for each other; the bird which warbles, the mammal which ruts, the insect which hums while pursuing the female with implacable tenacity, at the risk of their own life, employing sometimes cunning, sometimes dexterity, and sometimes force to attain their object. The ardor of the female is not always much less, but she uses coquetry, pretending to resist, and simulates repulsion. The more eager the male, the more coquettish is the female. If we observe the amorous sport of butterflies and birds, we see what efforts it costs the male to attain his object. On the other hand when the male is clumsy and slow the female often comes toward him or at any rate does not resist him, for instance in certain ants the males of which are wingless while the females have wings. The final act always consists in intimate union at the moment of copulation.
In some animals Nature is prodigal in the means she employs to pursue her great object, reproduction, by aid of the sexual appetite. The apiary raises hundreds of male bees. As soon as the single queen-bee takes wing for its nuptial flight all the males follow, but a single male only, the strongest and most nimble, succeeds in reaching her. In the intoxication of copulation he abandons all his genital organs to the body of the queen and dies. The other males, now useless, are all massacred in autumn by the working bees.
Sexual connection among butterflies of the Bombyx family is no less marvelous. They live for months as caterpillars and sometimes for two years as chrysalids, hibernating in a cocoon in some corner of the earth or in the bark of trees. Finally the butterfly, brilliantly colored, emerges from the cocoon and spreads its wings. It only possesses, however, a rudimentary intestinal canal for the short life which remains, for it does not require much nourishment and is only devoted to sexual connection. The female remains quiet and waits. The male, furnished with large antennæ which perceive the odor of the female at a distance of several kilometers, commences an infatuated flight through the woods and fields, as soon as his wings are sufficiently strong. His sole object is to reach the female. Here again there are numerous competitors. The one who arrives first possesses the female, but expires shortly afterward. His competitors die also, exhausted by their long flight and by starvation, but without having attained their object. After copulation, the female searches for the green plants which will ensure a long caterpillar life for her offspring. There she deposits her fecundated eggs in considerable numbers and then expires in her turn, like a faded flower which has fulfilled the object of its existence and falls after leaving the fruit in its place.
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.
The mechanism of appetites is thus a lower mechanism and has its seat in the primitive nervous centers. As Yersin has proved, a cricket deprived of its brain may copulate so long as the sensory irritations can reach the sexual nervous centers.
We can thus say that the mechanism of appetites belongs to automatic actions deeply inherited by phylogeny. Although complicated and composed of coördinated reflex movements which follow one another in regular succession, it has no actual power of modifying the so-called voluntary acts, which depend entirely on the cerebral hemispheres, and of which we men only have a conscious feeling. The appetites are not capable of adapting themselves to new circumstances and cease to be produced when the chain is interrupted. We are obliged to admit that the instincts or appetites are accompanied by a sub-conscious introspection which, as such, can hardly enter into direct relation with our higher consciousness, that is, with our ordinary consciousness in the waking state.
In spite of this, when their intensity increases, the appetites overcoming the central nervous resistances, reach the cerebral hemispheres, and consequently our introspection or higher consciousness, under a synthetic or unified appearance, and influence in a high degree the cerebral activities, which are reflected in association with all the elements of what we call our mind in the proper sense of the term, that is to say, our intellect, sentiments and will. It is from this point of view that sexual appetite must be considered in order to make it comprehensible. Love, with all that appertains to it, belongs as such to our mind, that is, to the activity of our cerebral hemispheres, but it is produced there by a secondary irradiation from the sexual appetite, which alone concerns us at present. We may also remark that sexual ideas when once awakened in the cerebral hemispheres by sexual appetite, are worked up there by the attention, that is to say by concentrated cerebral activity, then associated with other ideas, which on their side react strongly on the sexual appetite, developing or paralyzing it, attracting or repelling it, or finally transforming its attributes and objects.