Owing to the flexibility of the tail, the movements of the tail-fin, or "flukes," which sometimes measures eighteen feet across, are exceedingly extensive, whilst its power may be estimated by the gigantic bundles of round tendons, which pass on either side the loins, to be inserted into its base. Whether wielded in sportive mood or in anger, its action is marked by rapidity and ease, and when struck forcibly on the surface of the ocean, produces a report which may be heard at a considerable distance. In progression, the action of this organ is precisely the reverse of that of the tail of the lobster, for whilst the latter animal swims backward by striking the water with its tail from behind forwards, the cachalot and other cetaceans swim forward by striking with their flukes in the contrary direction, the fin being brought beneath the body by an oblique and unresisting movement; while the act of springing it back and straightening the tail propels the animal ahead with an undulating or leaping gait. When employed offensively the tail is curved in a direction contrary to that of the object aimed at, and the blow is inflicted by the force of the recoil. The lower jaw appears diminutive, slender, and not unlike the lower mandible of a bird. When the mouth is closed it is received within the soft parts pendent from the border of the upper jaw, and is nearly concealed by them. True and serviceable teeth are situated only in the lower jaw, and are received into corresponding sockets in the upper jaw. In aged males they are of great solidity and size, attaining a weight of from two to four pounds each; their entire structure is ivory. This powerful armament shows us at once that the food of the cachalot must be very different from that of the whalebone cetaceans; it generally consists of cuttle-fish, many kinds of which are ejected from its stomach when it is attacked by the boats, as well as after death. Owing to the great projection of the snout beyond the lower jaw, it may be requisite for this whale to turn on its side or back to seize its more bulky prey; a supposition strengthened by the fact that, when the animal attacks a boat with its mouth, it invariably assumes a reversed posture, carrying the lower jaw above the object it is attempting to bite. As long as it continues on the surface of the sea, the cachalot casts from its nostril a constant succession of spouts, at intervals of ten or fifteen seconds. As in all whales, the jets are not, as frequently imagined, water-columns, but a thick white mist ejected by one continual effort to the height of six or eight feet, and rushing forth with a sound resembling a moderate surf upon a smooth beach. The peculiar fat or sperm which renders the cachalot so valuable, is chiefly situated in the head. _Junk_ is the name given by the fishermen to a solid mass of soft, yellow, and oily fat, weighing between two and three tons, based on the upper jaw, and forming the front and lower part of