I don't know whether anyone has ever remarked that the caduceus of Mercury represents two serpents coupled. To describe the caduceus is to describe the love mechanism of ophidians. The bifurcated penis penetrates the vagina, the bodies interlace fold on fold while the two heads rise over the stiffened coils and look fixedly at each other, for a long time, eye gazing into eye.
Certain fish have penial organs; they can then realize true copulation; thus dog-fish, bounce, sharks, sea-hinds (_biches_). The males grip the females and hold them with hooks often formed at the expense of the abdominal fin, by cartilaginous pieces which penetrate the female orifice and serve as slide to the penis. The male skate seizes the female, turns her over, clamps himself to her, belly to belly, holds her with his penial tentacles and finishes the coupling, releasing his seed which flows into the cloaca. The operation is repeated several times; separated by the emission of skatelets who are born alive, it continues until the female has discharged the greater part of her eggs.
[1] Here R. de G. uses the term _marmotte_; up to this the word I have translated marmoset has been ouistiti.
_II. Copulation (continued).--Arthropodes.--Scorpions.--Large aquatic crustaceans.--Small crustaceans.--The hydrachne.--Scutilary.--Cockchafer.--Butterflies.-- Flies, etc.--Variation of animals' sexual habits._
Among insects, batrachians, and mollusks one finds the most curious modes of fecundation and those furthest removed from the usual mechanism of mammals; before coming to that we will give a few examples, toward forming an idea of the sexual habits of various species chosen from the arthropodes. In scorpions, let us say, terrestrial representatives of aquatic crustaceans: the two sexes are identical, genital organs usually invisible, hidden between the abdomen and the cephalothorax, the front part of it where the head without neck is prolonged directly into the thorax. The male is provided with two rigid penes englobed in a sheath--double but forming a single canal; holding the female belly to belly he inserts them in the vulva, one branch bending to the left, the other to the right toward each of the two oviducts. Same mechanism in crustaceans, save in the rare cases when they are hermaphrodite. Lobsters, langousts, écrevisses, crabs, like the scorpion, couple in a manner singularly resembling that of humans. Curious spectacle, that of the hen lobster attacked by the male, turned on her back, patiently permitting him to stretch over her, enlacing her claws and his pincers! Vision of a sabbat which Callot or Doré would only have painted in fear. Perhaps one would consider this before opening the armoured belly of these beasts who have bred their species among algæ, and in holes of the rocks? The genital glands of crustaceans are excellent; people gladly eat those of the sea-anemone; the only good part of these spiny animals. The males of the greater crustaceans have erectile ejectory canals, rising in the form of double prong between the forefeet; the females are correspondingly provided with two vulvæ opening in the third sternal segment, or at the base of the feet corresponding to this segment. Copulation is effected by quick acts, reiterated two or three times, lasting a quarter of an hour. The male of the fresh water prawn who swims leaning on his side, holds his female between his claws and progresses by bounds; she is much smaller than he is. Same mechanism in aselle and talitre or sea-flea.