AN OCTOPUS ON ITS BACK AT BAY, LEFT HIGH AND DRY BY THE RETREATING TIDE.
In this attitude the octopus can use its many-suckered tentacles and its formidable parrot-like beak as defensive weapons.
Having no jointed limbs, molluscs are dependent upon some other mechanical adaptation for their powers of locomotion. This, in the majority of species, is represented by a modification of the lower surface of the animal's body, which is so richly supplied with muscular tissues as to constitute an effective creeping-base. As a locomotive organ this muscular area is usually known as the "foot."
Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.
OCTOPODS.
A blue-spotted West Australian species.
Of living molluscs some 50,000 distinct species have been recorded. The great majority of these organisms are, as is well known, marine. A very considerable number, however, are inhabitants of fresh-water; while a yet smaller proportion, like the Slugs and Snails and their allies, are especially adapted for a terrestrial existence. Excepting two relatively small and inconspicuous groups, the great natural division or sub-kingdom of Molluscs is separated by systematic zoologists into three main sections or classes. The particular modification of the locomotive organ, or foot, serves, on the one hand, to readily distinguish the first or most highly organised group from the second or central class; while the third or lowest one is as clearly separated from the second and first by the character of the shell. The first and most highly developed section includes such species as the Octopus, the Cuttle-fish, the Squid, and the several varieties of Nautiluses; to the second or central group are referred all the marine and terrestrial Slugs and Snails with their innumerable modifications; while the third and lowest group comprises all the double-shelled or bivalve forms, such as Oysters and Mussels.
Photo by W. Saville-Kent, F.Z.S.] [Milford-on-Sea.