Those birds which are known as "apodes"[1] fly the most of all, because they are deprived of the use of their feet. By some persons they are called "cypseli." They are a species of swallow which build their nests in the rocks, and are the same birds that are to be seen everywhere at sea; indeed, however far a ship may go, however long its voyage, and however great the distance from land, the apodes never cease to hover around it. Other birds settle and come to a stand, whereas these know no repose but in the nest; they are always either on the wing or else asleep.