Even in the hermaphroditic slugs (Limax maximus) the process of courtship is slow and elaborate. It has been described by James Bladon ("The Loves of the Slug [Limax cinereus]," Zoölogist, vol. xv, 1857, p. 6272). It begins toward midnight on sultry summer nights, one slug slowly following another, resting its mouth on what may be called the tail of the first, and following its every movement. Finally they stop and begin crawling around each other, emitting large quantities of mucus. When this has constituted a mass of sufficient size and consistence they suspend themselves from it by a cord of mucus from nine to fifteen inches in length, continuing to turn round each other till their bodies form a cone. Then the organs of generation are protruded from their orifice near the mouth and, hanging down a short distance, touch each other. They also then begin again the same spiral motion, twisting around each other, like a two-strand cord, assuming various and beautiful forms, sometimes like an inverted agaric, or a foliated murex, or a leaf of curled parsley, the light falling on the ever-varying surface of the generative organs sometimes producing iridescence. It is not until after a considerable time that the organs untwist and are withdrawn and the bodies separate, to crawl up the suspending cord and depart.
Some snails have a special organ for creating sexual excitement. A remarkable part of the reproductive system in many of the true Helicidæ is the so-called dart, Liebespfeil, or telum Veneris. It consists of a straight or curved, sometimes slightly twisted, tubular shaft of carbonate of lime, tapering to a fine point above, and enlarging gradually, more often somewhat abruptly, to the base. The sides of the shaft are sometimes furnished with two or more blades; these are apparently not for cutting purposes, but simply to brace the stem. The dart is contained in a dart-sac, which is attached as a sort of pocket to the vagina, at no great distance from its orifice. In Helix aspersa the dart is about five-sixteenths of an inch in length, and one-eighth of an inch in breadth at its base. It appears most probable that the dart is employed as an adjunct for the sexual act. Besides the fact of the position of the dart-sac anatomically, we find that the darts are extended and become imbedded in the flesh, just before or during the act of copulation. It may be regarded, then, as an organ whose functions induce excitement preparatory to sexual union. It only occurs in well-grown specimens. (Rev. L. H. Cooke, "Molluscs," Cambridge Natural History, vol. iii, p. 143.)
Racovitza has shown that in the octopus (Octopus vulgaris) courtship is carried on with considerable delicacy, and not brutally, as had previously been supposed. The male gently stretches out his third arm on the right and caresses the female with its extremity, eventually passing it into the chamber formed by the mantle. The female contracts spasmodically, but does not attempt to move. They remain thus about an hour or more, and during this time the male shifts the arm from one oviduct to the other. Finally he withdraws his arm, caresses her with it for a few moments, and then replaces it with his other arm. (E. G. Racovitza, in Archives de Zoölogie Expérimentale, quoted in Natural Science, November, 1894.)
The phenomena of courtship are very well illustrated by spiders. Peckham, who has carefully studied them, tells us of Saitis pulex: "On May 24th we found a mature female, and placed her in one of the larger boxes, and the next day we put a male in with her. He saw her as she stood perfectly still, twelve inches away; the glance seemed to excite him, and he at once moved toward her; when some four inches from her he stood still, and then began the most remarkable performances that an amorous male could offer to an admiring female. She eyed him eagerly, changing her position from time to time so that he might be always in view. He, raising his whole body on one side by straightening out the legs, and lowering it on the other by folding the first two pairs of legs up and under, leaned so far over as to be in danger of losing his balance, which he only maintained by sliding rapidly toward the lowered side. The palpus, too, on this side was turned back to correspond to the direction of the legs nearest it. He moved in a semicircle for about two inches, and then instantly reversed the position of the legs and circled in the opposite direction, gradually approaching nearer and nearer to the female. Now she dashes toward him, while he, raising his first pair of legs, extends them upward and forward as if to hold her off, but withal slowly retreats. Again and again he circles from side to side, she gazing toward him in a softer mood, evidently admiring the grace of his antics. This is repeated until we have counted one hundred and eleven circles made by the ardent little male. Now he approaches nearer and nearer, and when almost within reach whirls madly around and around her, she joining and whirling with him in a giddy maze. Again he falls back and resumes his semicircular motions, with his body tilted over; she, all excitement, lowers her head and raises her body so that it is almost vertical; both draw nearer; she moves slowly under him, he crawling over her head, and the mating is accomplished."
The same author thus describes the courtship of Dendryphantes elegans: "While from three to five inches distant from her, he begins to wave his plumy first legs in a way that reminds one of a windmill. She eyes him fiercely, and he keeps at a proper distance for a long time. If he comes close she dashes at him, and he quickly retreats. Sometimes he becomes bolder, and when within an inch, pauses, with the first legs outstretched before him, not raised as is common in other species; the palpi also are held stiffly out in front with the points together. Again she drives him off, and so the play continues. Now the male grows excited as he approaches her, and while still several inches away, whirls completely around and around; pausing, he runs closer and begins to make his abdomen quiver as he stands on tiptoe in front of her. Prancing from side to side, he grows bolder and bolder, while she seems less fierce, and yielding to the excitement, lifts up her magnificently iridescent abdomen, holding it at one time vertical, and at another sideways to him. She no longer rushes at him, but retreats a little as he approaches. At last he comes close to her, lying flat, with his first legs stretched out and quivering. With the tips of his front legs he gently pats her; this seems to arouse the old demon of resistance, and she drives him back. Again and again he pats her with a caressing movement, gradually creeping nearer and nearer, which she now permits without resistance, until he crawls over her head to her abdomen, far enough to reach the epigynum with his palpus." (G. W. Peckham, "Sexual Selection of Spiders," Occasional Papers of the Natural History Society of Wisconsin, 1889, quoted in Nature, August 21, 1890.)
The courtship of another spider, the Agelena labyrinthica, has been studied by Lécaillon ("Les Instincts et les Psychismes des Araignées," Revue Scientifique, Sept. 15, 1906.) The male enters the female's web and may be found there about the middle of July. When courtship has begun it is not interrupted by the closest observation, even under the magnifying glass. At first it is the male which seeks to couple and he pursues the female over her web till she consents. The pursuit may last some hours, the male agitating his abdomen in a peculiar way, while the female simply retreats a short distance without allowing herself to be approached. At last the female holds herself completely motionless, and then the male approaches, seizes her, places her on her side, sometimes carrying her to a more suitable part of the web. Then one of his copulative apparatus is applied to the female genital opening, and copulation begins. When completed (on an average in about two hours) the male withdraws his copulatory palpus and turns over the female, who is still inert, on to her other side, then brings his second copulatory apparatus to the female opening and starts afresh. When the process is definitely completed the male leaves the female, suddenly retiring to a little distance. The female, who had remained completely motionless for four hours, suddenly runs after the male. But she only pursues him for a short distance, and the two spiders remain together without any danger to either. Lécaillon disbelieves the statement of Romanes (in his Animal Intelligence) that the female eats the male after copulation. But this certainly seems to occur sometimes among insects, as illustrated by the following instance described by so careful an observer of insects as Fabre.
The Mantis religiosa is described by Fabre as contemplating the female for a long time in an attitude of ecstasy. She remains still and seems indifferent. He is small and she is large. At last he approaches; spreads his wings, which tremble convulsively; leaps on her back, and fixes himself there. The preludes are long and the coupling itself sometimes occupies five or six hours. Then they separate. But the same day or the following day she seizes him and eats him up in small mouthfuls. She will permit a whole series of males to have intercourse with her, always eating them up directly afterward. Fabre has even seen her eating the male while still on her back, his head and neck gone, but his body still firmly attached. (J. H. Fabre, Souvenirs Entomologiques, fifth series, p. 307.) Fabre also describes in great detail (ibid., ninth series, chs. xxi-xxii) the sexual parades of the Languedoc scorpion (Scorpio occitanus), an arachnid. These parades are in public; for their subsequent intercourse the couple seek complete seclusion, and the female finally eats the male.
An insect (a species of Empis) has been described which excites the female by manipulating a large balloon. "This is of elliptical shape, about seven millimeters long (nearly twice as long as the fly), hollow, and composed entirely of a single layer of minute bubbles, nearly uniform in size, arranged in regular circles concentric with the axis of the structure. The beautiful, glistening whiteness of the object when the sun shines upon it makes it very conspicuous. The bubbles were slightly viscid, and in nearly every case there was a small fly pressed into the front end of the balloon, apparently as food for the Empis. In all cases they were dead. The balloon appears to be made while the insect is flying in the air. Those flying highest had the smallest balloons. The bubbles are probably produced by some modification of the anal organs. It is possible that the captured fly serves as a nucleus to begin the balloon on. One case of a captured fly but no balloon was observed. After commencing, it is probable that the rest of the structure is made by revolving the completed part between the hind legs and adding more bubbles somewhat spirally. The posterior end of the balloon is left more or less open. The purpose of this structure is to attract the female. When numerous males were flying up and down the road, it happened several times that a female was seen to approach them from some choke-cherry blossoms near by. The males immediately gathered in her path, and she with little hesitation selected for a mate the one with the largest balloon, taking a position upon his back. After copulation had begun, the pair would settle down toward the ground, select a quiet spot, and the female would alight by placing her front legs across a horizontal grass blade, her head resting against the blade so as to brace the body in position. Here she would continue to hold the male beneath her for a little time, until the process was finished. The male, meanwhile, would be rolling the balloon about in a variety of positions, juggling with it, one might almost say. After the male and female parted company, the male immediately dropped the balloon upon the ground, and it was greedily seized by ants. No illustration could properly show the beauty of the balloon." (Aldrich and Turley, "A Balloon-making Fly," American Naturalist, October, 1899.)
"In many species of moths the males 'assemble' around the freshly emerged female, but no special advantage appears to attend on early arrival. The female sits apparently motionless, while the little crowd of suitors buzz around her for several minutes. Suddenly, and, as far as one can see, without any sign from the female, one of the males pairs with her and all the others immediately disappear. In these cases the males do not fight or struggle in any way, and as one watches the ceremony the wonder arises as to how the moment is determined, and why the pairing did not take place before. Proximity does not decide the point, for long beforehand the males often alight close to the female and brush against her with fluttering wings. I have watched the process exactly as I have described it in a common Northern Noctua, the antler moth (Charæax graminis), and I have seen the same thing among beetles." (E. B. Poulton, The Colors of Animals, 1890, p. 391.) This author mentions that among some butterflies the females take the active part. The example here quoted of courtship among moths illustrates how phenomena which are with difficulty explicable by the theory of sexual selection in its original form become at once intelligible when we realize the importance of tumescence in courtship.
Of the Argentine cow-bird (Molothrus bonariensis) Hudson says (Argentine Ornithology, vol. i, p. 73): "The song of the male, particularly when making love, is accompanied with gestures and actions somewhat like those of the domestic pigeon. He swells himself out, beating the ground with his wings, and uttering a series of deep internal notes, followed by others loud and clear; and occasionally, when uttering them, he suddenly takes wing and flies directly away from the female to a distance of fifty yards, and performs a wide circuit about her in the air, singing all the time. The homely object of his passion always appears utterly indifferent to this curious and pretty performance; yet she must be even more impressionable than most female birds, since she continues scattering about her parasitical and often wasted eggs during four months in every year."