On the 25th of January the ocean was entirely deserted; the _Nautilus_ passed the day on the surface, beating the waves with its powerful screw and making them rebound to a great height. Who under such circumstances would not have taken it for a gigantic cetacean? Three parts of this day I spent on the platform. I watched the sea. Nothing on the horizon, till about four o’clock a steamer running west on our counter. Her masts were visible for an instant, but she could not see the _Nautilus_, being too low in the water. I fancied this steamboat belonged to the P. O. Company, which runs from Ceylon to Sydney, touching at King George’s Point and Melbourne. At five o’clock in the evening, before that fleeting twilight which binds night to day in tropical zones, Conseil and I were astonished by a curious spectacle. It was a shoal of argonauts travelling along on the surface of the ocean. We could count several hundreds. They belonged to the tubercle kind which are peculiar to the Indian seas. These graceful molluscs moved backwards by means of their locomotive tube, through which they propelled the water already drawn in. Of their eight tentacles, six were elongated, and stretched out floating on the water, whilst the other two, rolled up flat, were spread to the wing like a light sail. I saw their spiral-shaped and fluted shells, which Cuvier justly compares to an elegant skiff. A boat indeed! It bears the creature which secretes it without its adhering to it. For nearly an hour the _Nautilus_ floated in the midst of this shoal of molluscs. Then I know not what sudden fright they took. But as if at a signal every sail was furled, the arms folded, the body drawn in, the shells turned over, changing their centre of gravity, and the whole fleet disappeared under the waves. Never did the ships of a squadron manœuvre with more unity. At that moment night fell suddenly, and the reeds, scarcely raised by the breeze, lay peaceably under the sides of the _Nautilus_.