Dr. Roget, in his _Bridgewater Treatise_, under the head of “_Cephalopoda_,” states that “we now arrive at a highly interesting family of mollusca, denominated _Cephalopoda_, and distinguished above all the preceding orders by being endowed with a much more elaborate organization and a far wider range of faculties. The _Cephalopoda_ have been so named from the position of certain organs of progressive motion which are situated on the head, and, like the tentacula of the polypus, surround the opening of the mouth. These feet, or arms, or tentacula, if we choose to call them so, are long, slender, and flexible processes, exceedingly irritable and contractile in every part, and provided with numerous muscles, which are capable of moving or twisting them in all directions with extraordinary quickness and precision. They are thus capable of being employed as instruments not only of progressive motion, but also of prehension. For this purpose they are, in many species, peculiarly well adapted, because, being perfectly flexible as well as highly muscular, they twine with ease round any object of any shape, and grasp it with prodigious force. In addition to these properties, they derive a remarkable power of adhesion to the surfaces of bodies from their being furnished with numerous suckers all along their inner sides. Each of these suckers is usually supported on a narrow neck or pedicle, and strengthened at its circumference by a ring of cartilage. Their internal mechanism is more artificial than the simple construction already described; for when the surface of the disk is fully expanded, it is formed of a great number of small, slender pieces, resembling teeth, closely set together, and extending from the inner margin of the cartilaginous rings in the form of converging radii to within a short distance of the centre, where they leave a certain aperture. “In the flattened state of the sucker, this aperture is filled by the projecting part of a softer substance, which forms an interior portion, capable of being detached from the flat circle of the teeth when the sucker is in action, and of leaving an intervening cavity. It is evident that by this mechanism, which combines the properties of an accurate valve with an extensive cavity for producing rarefaction, or the tendency to vacuum, the power of adhesion is considerably augmented. So great is the force with which the tentacula of the cuttle-fish adhere to bodies by means of this apparatus, that, while their muscular fibres continue contracted, it is easier to tear away the substance of the limb than to release it from its attachment. Even in the dead animal we have found that the suckers retain considerable powers of adhesion to any smooth surface to which they may be applied.