The cephalopods are scattered in vast numbers over the whole ocean, from the ice-bound shores of Boothia Felix to the open main; they seem, however, to be most abundant in temperate latitudes. Some, like the common poulp, constantly frequent the coasts, creeping among the rocks and stones at the bottom; others, like the Cirroteuthis and Ommastrephes, roam about the high seas at a vast distance from the land.
They are generally nocturnal or vespertine in their habits; they abound towards evening and at night on the surface of the seas, but sink to a greater depth, or retire into the crevices of the rocks, as soon as the sun rises above the horizon. Some are of a recluse disposition, and lead a solitary life in the anfractuosities of the littoral zone; others, of a more social temper, wander in large troops along the shores, or over the vast plains of ocean.
Possessing the organs of sense, and the means of locomotion in a high degree of development, the cephalopods may naturally be expected to be far more active and intelligent than the inferior orders of the molluscs. On moonlight nights, among the islands of the Indian Archipelago, Mr. Adams frequently observed the Sepiæ and Octopi in full predatory activity, and had considerable difficulty and trouble in securing them, so great was their restless vivacity, and so vigorous their endeavours to escape. "They dart from side to side of the pools," says the naturalist in his entertaining and instructive account of his journey to those distant gems of the tropical sea, "or fix themselves so tenaciously to the surface of the stones by means of their suckers that it requires great force and strength to detach them. Even when removed and thrown upon the sand, they progress rapidly, in a sidelong shuffling manner, throwing about their long arms, ejecting their ink-like fluid in sudden violent jets, and staring about with their big shining eyes (which at night appear luminous, like a cat's) in a very grotesque and hideous manner."
At the Cape de Verd islands, Mr. C. Darwin was also much amused by the various arts to escape detection used by a cuttle-fish, which seemed fully aware that he was watching it. Remaining for a time motionless, it would then stealthily advance an inch or two, like a cat after a mouse, and thus proceeded, till, having gained a deeper part, it darted away, leaving a dusky train of ink, to hide the hole into which it had crawled.