Mucianus relates that he has seen, in the Propontis, another curious resemblance to a ship in full sail. There is a shell-fish, he says, with a keel, just like that of the vessel which we know by the name of acatium, with the stern curving inwards, and a prow with the beak attached. In this shell-fish there lies concealed also an animal known as the nauplius, which bears a strong resemblance to the sæpia, and only adopts the shell-fish as the companion of its pastimes. There are two modes, he says, which it adopts in sailing; when the sea is calm, the voyager hangs down its arms, and strikes the water as with a pair of oars; but if the wind invites, it extends them, employing them by way of a helm, and turning the mouth of the shell to the wind. The pleasure experienced by the shell-fish is that of carrying the other, while the amusement of the nauplius consists in steering; and thus, at the same moment, is an instinctive joy felt by these two creatures, devoid as they are of all sense, unless, a natural antipathy to man—for it is a well-known fact, that to see them thus sailing along, is a bad omen, and that it is portentous of misfortune to those who witness it.[140] The cray-fish, which belongs to the class of bloodless animals, is protected by a brittle crust. This creature, like the crab, keeps itself concealed for five months. But at the beginning of spring both of them, after the manner of snakes, throw off old age, and renew their coverings. While other animals swim on the water, cray-fish float with a kind of action like creeping. They move onwards, if there were nothing to alarm them, in a straight line, extending on each side their horns, which are rounded at the point by a ball peculiar to them; but when alarmed, they straighten these horns, and proceed with a sidelong motion. They use these horns when fighting with each other. The cray-fish is the only animal that has the flesh in a pulpy state, and not firm and solid, unless it is cooked alive in boiling water. The cray-fish frequents rocky places, the crab spots which present a soft surface. In winter they both choose such parts of the shore as are exposed to the heat of the sun, in summer they withdraw to the shady recesses of deep inlets of the sea. All fish of this kind suffer from the cold of winter, but become fat during autumn and spring, particularly during the full moon; for the warmth of that luminary, as it shines in the night, renders the temperature of the weather more moderate.