Page:The New International Encyclopædia 1st ed. v. 04.djvu/502

CEPHALOPODA. 430 CEPHALOPODA. other mollusks. and is generally fumisliod with t«i) hirge aud pioiiiinent eyes that are very simi- lar in structure to those of vertebrate luiiuials. The nervous system is very well developed, and is more eentrnlized than in other mollusks. The panalia are well eoncentrated in what may he called the lirain. which lies aliove and aroiuid the (esophagus, and is more or less wholly included within the cartilage of the head. Krom this luain nerves go to the various organs and parts of the body. The senses of hearing and smell are regarded as weak, but that of taste seems to be strong. The mouth oinms in the midst of the circlet of arms. It is furnished with a strong, horny beak of two jaws that move vertically like those of a parrot, but the upper jaw is the shorter of the two. In addition t.o the jaws, there is a lingual ribbon covered with minute teeth, like that of the odontophore of the gastropods. The digestive a|)j)aratus is ' very complicated. The gullet swells out into a crop, and there is a gizzard as muscular as that of a bird. The intestine, after a few convolu- tions, terminates in the cavity which contains the gills at the base of the hyponome, by which the water is ejected from the mantle-cavity after having sujjplied air for respiration. There are two gills in most living cephalopods, one on each side, lying close to the body-wall ; the only exceptions to this rule arc in the three species of nautilus which have four gills, a pair on each side. Each gill consists of many mem- branous plates fixed to two sides of a stalk. The heart in the Tetrabranchiata consists of a single ventricle only: but there are fonr auricles, one for each gill: the Dibranchiata have two auricles, one f(U' each gill. In the latter group, moreover, are found two contra<:tile reservoirs (branchial or respiratory hearts), one for each gill, by which the blood is pumped into these organs'. The arms or feet are very numerous in the Tetrabranchiata, and are not ]irovided with suck- ers, bu*. are hollow and furnished with long, re- tractile tentacles. In the Dibranchiata the arms arc cither eight or ten in number, are furnished with suckers (acetabula). and in the ten-armed genera two of the arms are much longer than the others and dilVer from them in form. The suck- ers are niu.scular disks, with cartilaginous rims, capable of exact application to any object, with central cavities the bottoms of which can be re- tracted at will to form a vacumn. and thus ren- der the adhesion of the sucker close and firm after the manner of a cupping-glass. The poulpe or oeto|uis has each of its eight flexible arms crowded with 1'20 p;iirs of such suckers, and as animals of this kind, with arms several feet long, exist commonly in the tropics, they are considered dangerous neighbors. Still more for- midable, however, are the hook-squids of the south seas, the two long arms of which have sinkers furnished in the centres with hooks that enter the flesh of any creature upon which the squid may lay hold. The sexes are distinct in all cephalopods. In most cases the male is smaller than the female, lie differs, moreover, in the asynunclry of his arms, one of which is more or less modified to form a eopulatory organ. In two or three genera this modified arm breaks ofT from the body dur- ing copulation, and finds its way into the mantlc- eavity of the female, where it empties itself of the male spcrm-cclls which it carries. The first zoi'dogist who found such an arm in the mantle- cavity of a female argonaut (q.v. ) mistook it for a parasitic worm and called it "hectocotyhis' (hundred cups), from the numeroi^s suckers which it bears. When its true nature was dis- covered, it was called a 'hectocotilized' arm, and the term is still ised in that connection. The eggs have a horny covering, and after their extrusion from the parent they become aggluti- nated into masses of various forms. The young from the first very much resemble the matAire animals, except in size. All dibranchiates are provided with a peculiar organ of defense, called an "ink-bag,' which is absent in the tetrabranchiates. This ink-bag is filled with a peculiar secretion, capable of being expelled at will through the hyponome to darken the surrounding water and thus facilitate the escape of the cephalopod. (See Sepia.) The tetrabranchiate cephalopods have a chambered shell which is described in further detail below. (See also X.wtilus. ) The dibranchiates have no true external shells — the shell of the female argonaut (q.v.) being scarcely an exception — but they have an internal shell, homologous to the external tetrabranchiate shell, known as cuttlefish - bone. etc.. sometimes merely rudi- mentary, included lietween the fohls of the man- tle and apparently serving to support tlie organs and to give rigidity to the liody while swinnning. The cephalopods are all very voracious; they are carnivorous, feeding on fish, mollusks, cris- taceans, etc. Even a powerful crab is not safe from the attack of a dibranchiate cephalopod little bigger than itself: the arms of the octopus, so abundantly provided with suckers, seize the orab, tranuiiel every movement, and the parrot- like beak is strong enough to break the hard shell. Cephalopods are all marine, and they are found in the temperate and tropical parts of all seas. Nautilus, the single modern genus of the tetral)ranchiates, with three species, lives in the Indian and South Pacific oceans, where it creeps on the bottom, near the shore, in comparatively sliallow water. The dibranchiates are quite abundantly represented at the present time. The members of the two living orders, Sepioidea and Oetopoda. have rather ditl'erent habits and corre- spondingly difi'erent habitats. The Oetopoda, with round, siu-like bodies and eight arms, are essentially creepers on the bottom, like the poulpe or octopus. They live in shallow water along the shore, hiding in cavities during the day and creeping about over the rocks of the bottom by night. They are also capable, when they find themselves in large bodies of water, of swinnning rapidly by means of the hyponome. They are often handsomely colored creatures, but they are generally repulsive objects. The Decapoda have long, slender bodies and ten arms, of which two are nuich longer than the rest. They are found in all seas, often in deep water. Many of them congregate in hordes in the open sea, swimming about with great rapid- ity. Unlike the octopods, they seldom creep on the bottom, the hyponome being the principal organ of locomotion. Their motions are ex- tremely graceful, and they are often beautifully colored. In size the living cephalopods range from a few inches in length (Sepiola) to many feet. The largest inverlebrntc is undoubtedly a giant squid ( Architeuthis) of the Xcwfoundland