with a sudden rush flings himself upon her, and apparently thrusts the penis into her mantle cavity, when at once the whole arm breaks off from his body and remains attached to her person, retaining its vitality, strange as it may seem, for some considerable time, during which, no doubt, the spermatozoa are slowly making their way out of the spermatophore and along the channel prepared for their reception. That the Cuttle-fish are polyandrous there seems to be little room for doubt, inasmuch as no less than four such detached arms have been found beneath the mantle of one female. With the majority of the Cuttle-fish and Octopus tribe the arm is not detached, but when it is so, and this occurs in all the species belonging to three different genera, a new arm is grown. [Illustration: Plate 41. SOME REMARKABLE METHODS OF “COURTSHIP.” 1. The female Argonaut and her egg-casket. 2 and 3. The male Argonaut and his “hectocotylized” arm. 4. A Cuttle-fish (_Ocyhöe catenulata ♂_), showing the “hectocotylized” arm described in the text, and the “spermatophore” at the base of the long filament. Face page 268.] 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.