Page:Natural History, Mollusca.djvu/72

60 gliding by. The instant that the Cuttle feels the contact, instinctively, and with the speed of lightning, it retracts the fleshy piston; a vacuum is thus created, and the edges of the disk are pressed against the surface of the victim, with a force equal to the weight of the water that is above it, added to the weight of the atmosphere. If need be, as when the victim makes strenuous efforts to escape, the vacuum, and consequently the adhesion, is increased by the withdrawal of the membranous disk.

STRUCTURE OF SUCKER.

This apparatus, powerful as it is, is but one out of a thousand instruments of the same kind with which the animal is furnished. Our common Poulpe (Octopus vulgaris) has eight tentacular arms, and every one of these carries one hundred and