Page:Natural History, Mollusca.djvu/71

Rh armed with a pair of horny or calcareous mandibles, which bear a strong resemblance to the bill of a parrot, acting vertically one upon the other. Its situation is the bottom of a subconical cavity, formed by the base of the numerous fleshy tentacular appendages which surround it, and which have been termed arms by some naturalists, and feet by others."

These fleshy flexible feet are characteristic of the Class, and give to it its systematic appellation of Cephalopoda, signifying head-footed. They are instruments of locomotion; the animal being enabled to crawl awkwardly upon this circle of feet, head downwards. But their chief use to the animal is as organs for the seizing and holding of prey; and for this purpose they are eminently qualified. Each arm is furnished with a double row of sucking disks, each of which on being applied to any surface adheres to it at the will of the animal with immense force, so that it is easier to tear away the substance of the limb while the creature maintains its hold, than to release it from its attachment; and even after death, the suckers continue to retain a considerable power of adhesion.

The manner in which these suckers act, will be understood by a reference to the principle of a cupping-glass. Each one consists of a firm fleshy or cartilaginous ring, across which a disk of muscular membrane is stretched, with a circular aperture in the centre. A cone-shaped mass of flesh fills this aperture, like a piston, capable of being drawn backward. The membranous disk itself can also be drawn in. Now, let us suppose that one of the sucking disks of a tentacle touches any object fit for prey, such as a fish, for example,