The manner in which the eight-armed and ten-armed cephalopods capture their prey is similar in principle and plan, but differs in action in accordance with their mode of life. The ordinary habit of the octopus is either to rest suspended to the side of a rock to which it clings with the suckers of several of its arms, or to remain lurking in some favourite cranny; its body thrust for protection and concealment well back in the interior of the recess; its bright eyes keenly on the watch; three or four of its limbs firmly attached to the walls of its hiding place--the others gently waving, gliding, and feeling about in the water, as if to maintain its vigilance, and keep itself always on the alert, and in readiness to pounce on any unfortunate wayfarer that may pass near its den. To a shore-crab that comes within its reach the slightest contact with one of those lithe arms is fatal. Instantaneously as pull of trigger brings down a bird, or touch of electric wire explodes a torpedo or a mining fuse, the pistons of the series of suckers are simultaneously drawn inward, the air is removed from the pneumatic holders, and a vacuum created in each: the crab tries to escape, but in a second is completely pinioned: not a movement, not a struggle is possible; each leg, each claw is grasped all over by suckers, enfolded in them, stretched out to its fullest extent by them; the back of the carapace is completely covered by the tenacious disks, brought together by the adaptable contractions of the limb, and ranged in close order, shoulder to shoulder, touching each other; and the pressure of the air is so great that nothing can effect the relaxation of their retentive power but the destruction of the air-pump that works them, or the closing of the throttle-valve by which they are connected with it. Meanwhile the abdominal plates of the captive crab are dragged towards the mouth; the black tip of the hard horny beak is seen for a single instant protruding from the circular orifice in the centre of the radiation of the arms; and, the next, has crushed through the shell, and is buried deep in the flesh of the victim. [Illustration: FIG. 2.--THE OCTOPUS (_Octopus vulgaris_).]