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Show 306 :MOLLUSCA. CLASS I. CEPHALOPODA( I). Their mantle unites under the body, foJ•ming a muscular sac which envelopes all the viscera. In several, its sides are extend· ed into fleshy fins. The head projects from the opening of the sac ; it is rounded, furnished with two large eyes, and erowned with longer or shorter conical and fleshy arms or feet, ca. pable of being :flexed in every direction, and extremely vigor· ous, the surface of which is armed with suckers or cups, which enable them to adhere with great tenacity to every body they embrace. These feet are their instruments of prehension, natation, and walking. They swim with the head backwards, and crawl in all directions with the head beneath and the body above. A fleshy funnel placed at the opening of the sac, before the neck, affords a passage to the excretions. The Cephalopoda have two branchire within the sac, one on each side, resembling a highly complicated fern leaf; the great vena cava, having arrived between them, divides into two branches, which pour their contents into two fleshy ven· tricles, each of which is placed at the base of the branchire on its own side, and propels the blood into it. The two bran~hial veins communicate with a third ventricle, (1) M. de Blainville has changed this name to that of Cepltalophora. M. de Lamarck at fh-st united my Cepltalopoda and Gaateropoda undet• the coJDo mon name of Cephala, but having subsequently increased the number of classes, he resumed that of Cephalopoda. CEPHALOPODA. 307 situated near the bottom of the sac, which, by means of various arteries, distributes the blood to every part of the body. Respiration is effected by the water which flows into the sac and issues throl1gh the funnel. It appears that it can even penetrate into two cavities of the peritoneum, traversed by the vena cava in their passage to the branchire, and act upon the venous blood by means of a glandular appar!ltus attached to those veins. Between the base of the feet we :find the mouth armed with two stout horny jaws resembling the beak of a parrot. Between the jaws is a tongue bristling with horny points; the resophagus swells into a crop, and then communicates with a gizzard as :fleshy as that of a Bird, to which succeeds a third membranous and spiral stomach, which receives the bile from the two ducts of the very large liver. The intestine is simple and short. The rectum terminates in the funnel. These animals are remarkable for a peculiar and intensely black excretion, with which they darken the surrounding water when they wish to conceal themselves. It is produced by a gland; and held in reserve by a sac, variously situated, according to the species. Their brain, which is contained in a cartilaginous cavity of the head, gives off a cord on each side which produces a large ganglion in each orbit, whence are derived innumerable optic filaments; the eye consists of several membranes, and is covered by the skin which becomes diaphanous in that particular spot, sometimes forming folds which supply the want of eyelids. The ear is merely a slight cavity, on each side near the brain, without semicircular canals or an external Meatus, where a membranous sac is suspended which contains a little stone. The skin of these animals, of the Octopi particularly, changes colour in places, by spots, with a rapidity which greatly surpasses that of the Chameleon( I). The sexes are separated. The ovary of the female is in the (1) See Carus, Nov. Act. Nat. Cur., XII, part I, p. 320, and Sangiovanni, Ann. des Sc. Nat. XVI, p. 308. \ |