The Courtship of Animals

by W. P. Pycraft

As a rule, among these animals the males are smaller than the females. In the case of the Argonaut there is a yet more striking difference, for the female possesses a very beautiful shell in which she carries her eggs. This remarkable cradle, translucent and beautifully sculptured, she attaches to her person by means of a pair of arms which are expanded to form great lobes, almost but not quite completely covering the shell. The earlier naturalists believed that this shell served as a boat, and that the lobated arms were spread as sails! This supposed fact naturally caught the fancy of the poets, who seized upon it to point a moral and adorn a tale. Byron celebrated these imaginary feats of seamanship in the familiar lines:

The tender Nautilus who steers his prow,

The sea-born sailor of his shell-canoe.

and Pope bids us:

Learn of the little Nautilus to sail,

Spread the thin oar, and catch the driving gale.

Sir Richard Owen years ago, however, dispelled these pretty fancies, though the facts are surely as wonderful as the fables they have replaced. They afford, too, one of the most striking secondary sexual characters to be met with among the Mollusca; nowhere else, indeed, among the members of this group is so strange a cradle to be met with.

But little, unfortunately, is known of the behaviour of these animals, which are by far the most active of the Mollusca, and which also display no small degree of intelligence. Their eyes, which are of great size and complex structure, are undoubtedly far more effective organs of vision than are possessed by any other Molluscs. It is possible, therefore, that the sexes discover one another by sight; and it is certain that something in the nature of a “Courtship” takes place. The majority of the species, also, possess the most extraordinary powers of changing their coloration, especially during moments of great excitement. The magnificence of the hues which succeed one another, like a series of variegated blushes suffusing the whole body, may be one of the weapons in the armoury of Cuttle-fish love-making. In how far the “courtship” of the Cuttle-fish resembles that of terrestrial animals, however, is a matter on which at present nothing is really known. That even the comparatively sedentary species, like the Octopus, seize upon and hold territory is very improbable, for there is no need of such landed estates, inasmuch as the offspring are not tended and fed by the parents—this would indeed be a laborious task in the case of some of the “Squids” which lay between thirty thousand and forty thousand eggs! Having regard to the fact that the records of the reproductive habits of the Octopus tribe date back to the time of Aristotle, more than two thousand two hundred years ago—for he first drew attention to the hectocotylized arm—it is curious that so little has been gleaned during this vast space of time.

There are facts in regard to the sexual relationships of some of the Snails that are in nowise less remarkable than those just related of the Octopus tribe. Unlike the Octopuses, the Snails are hermaphrodite, nevertheless sexual congress takes place as with unisexual species: the eggs of the one being fertilized by the spermatozoa of the other. During this process the orgasm of the sexual act appears to be brought about by stabbing one another by means of a little dart formed of carbonate of lime, the dart burying itself in the flesh and apparently promoting a pleasurable, tingling sensation in the course of its journey. Speedily, no doubt, it becomes absorbed, the material being then available for the formation of a new dart.

This remarkable instrument, which is known as a “Love-dart,” or Spiculum amoris, assumes a different form in each species in which it occurs. In some the shaft is ridged like a bayonet, as in the case of the Garden Snail, in others the form assumed is that of an awl. These darts are formed within a special receptacle, or “dart-sac,” but so far no explanation as to the origin of these remarkable structures has even been hinted at. They do not seem to have been derived by the modification of some pre-existing organ serving a different function, as wings, for example, are derived from walking limbs, or as lungs are derived from air-sacs. Their origin is as mysterious as their use: for they are not found in all Snails, though they occur in one or two Slugs—which are degenerate Snails. But no other Molluscs save the Snails and one or two of their immediate allies are so armed.