Among the most remarkable curiosities is the animal which has the name[1] of nautilus, or, as some people call it, the pompilos. Lying with the head upwards, it rises to the surface of the water, raising itself little by little, while, by means of a certain conduit in its body, it discharges all the water, and this being got rid of like so much bilge-water as it were, it finds no difficulty in sailing along. Then, extending backwards its two front arms, it stretches out between them a membrane[2] of marvellous thinness, which acts as a sail spread out to the wind, while with the rest of its arms it paddles along below, steering itself with its tail in the middle, which acts as a rudder. Thus does it make its way along the deep, mimicking the appearance of a light Liburnian[3] bark; while, if anything chances to cause it alarm, in an instant it draws in the water, and sinks to the bottom.[4]