Respiratory Organs.—These are branehial, and the bronchitis are equal, symmetrical, and protected by the mantle under which they are concealed. The infundibulum, or funnel (entonnoir of the French), is a fleshy pipe or passage in frout of the neck, through which the respiratory currents' pass and the excrements are discharged. The young, as in other classes, respire more quickly than the adult. Dr. Coldstream saw an Eledone, one inch and a half in length, brenthe eighteen times in a minute, while another of the same species, four inches in length, breathed only ten times in a minute.
Circulating Organs.—Tho higher organised Cephalopoda present the remarkable circumstance of having three separate and well organised hearts: one for the circulation of the arterial blood through the body, the other two for the propulsion of the venous blood through each gill or respiratory organ. Only the first of these hearts, or the 'systemic,' is present in the Pearly Nautilus, which is, according to Owen, the typo of the lower order of the class. In both divisions the venous system is characterised by the glandular bodies appended to the branehial divisions of the vena cave, or main trunk.
Sexual Organs.—Separate and developed in distinct individuals. It in not determined whether impregnation is effected before the ova are excluded, during their exclusion, or afterwards. Cuvier was of opinion that fecundation is effected by arrosernent, as in the majority of fishes. The ovary of the female is situated in the bottom of the sac. Two oviducts receive the eggs from the ovary, and carry them out across two large glands, which envelop them with a viscous substance, and unite them together into bunches like grapes.
Brain and Senses.—The brain is included in a cartilaginous cavity in the head, and gives off on each side a nervous cord, which forms in each orbit a large ganglion, whence proceed innumerable optic nervous filaments. The eye is composed of numerous membranes, and covered by the skin, which becomes transparent in front of the organ, and sometimes forms folds which perform the office of eyelids. Owen has observed that the cornea of Russia is defended by a circular fold of integument, which can be completely closed by an orbicular sphincter in front of the eye—a structure which is probably required In this species in order to protect the cornea against the spicule of ice, with which Its native seas abound, especially in the summer or thawing season. In the Calarnary (Loligo) on the other hand, there is no tegumentary fold. The ear is nothing more than a small cavity hollowed out on each side near the brain, without semicircular canals or an external tube, and in this cavity is suspended a membranous sac containing a limpid fluid and a small compact stony substance or otolithe, a sort of osaiculum auditas.
Ink-Bags.—The excretion from these begs is of a deep black, and In those species in which it occurs (for it is not common to tho whole family) It Is produced by a gland appropriated to its secretion, and reserved in a small bag till the exigencies of the animal call for its effusion to cloud the surrounding water in order that it may conceal itself. It has been long considered that the Indian Ink imported from China is manufactured from this secretion, but Culler observes that M. It&musat has found nothing in Chinese authors confirmatory of this opinion. That it makes an excellent pigment even after having been buried for thousands of years in the earth Is proved by Dr. Bnekland's fossil ink, which ho submitted to a celebrated painter, who Immediately inquired from what colourmnn such good sepia might be procured.
The akin of the naked species is changeable, showing spots which brighten and fade with n rapidity superior to the cuticular changes of the chameleon.
Food.—Principally fishes and crustacean ; but there is little doubt that few animal matters come amino to these mollusks, for they are most voracious.
Oeographical Distribution.—Very wide. Hardly any sea is without some species of tho family. Captain Ross discovered a new genus (Rossia, Owen), in the Arctic Ocean, which has since been found in our own seas. Fabriciva describes two species which frequent the coasts of OreenInnd. (' Fauna Orcenlandica,' p. 3G1.) Utility.—The 'kali, especially that of the arms, is astable, and is considered very nutrition& Though neglected in the British Islands, it is brought to table in other countries. The arms, cut into portions and prepared for cookery, are to be frequently seen in the Neapolitan market. The evade-bone is used for erasures, and manufactured into 'pounce' of the shops. The prepared ink is capable of being made into a pigment. That the Naked Cephnlopods formed a favourite dish with the ancients, and were considered not unworthy of the most exquisite cookery, therein no doubt. (See for instance Athentens, Deipnosoph.' lib. i. vi., vol. i., p. 14 : lib. vii. lxxxvii et cxxx., vol. iii., pp. 140 et 199: lib. xiv. xviL, voL v., p. 255, Schweighiiuser's edition.) The natural division of the class is into those Cephalopods which are naked (Cephalopods nada), and those which are protected by an external shell (Cephalopoda testacea). Of the former, Sepia officinalls, the Common Cuttle-Fish, may be taken as an example ; and the following cut will give a general idea of the form of a naked Cephalo pod, but this varies in the different genera. In Sepia officinah's tho soft parts are supported by a firm calcareous bone, the well-known cuttle.bono of the shops, and in all the naked Cephalopods (not including Ocytho!) now existing, it would appear that sonic rudiment at least of a bony, horny, or cartilaginous support is to be found. (SErten.t.] The Nautilus Pompilius affords an example of the thstaceons Cephalopods, or thane which are protected by a shell. [Nat:minx] Professor Owen has however shown the necessity of dividing this order into two groups, which he proposes to call Ddirancltiata and Tetrabranehiata.
The Dibranchiata are characterised by possessing two branehim ; and to this division all the Naked Cepholopcula belong, such as the species of the genera Sepia, to which the Common Cuttle-Fish belongs, Le/igo, Octopus, Russia, and Ommastrepluv.
The Tetrabranchiata possess four branchim ; and to this division the Nautilus [Nat:minx], and the bulk of the fossil species of Cephalo poda known under tho names of Ammonites, Goniatiles, Ceratitea, belong. The extinct animals of this division are by far the most numerous.
None of the Tttraleanclaiala exist in the British seas ; there are however several forms of Dibranchiata, of which the following These are multitudinous, and in the bye-gone ages of the world appear to have been powerful instruments for keeping down the other tribes of ancient Testaceans, Crustaceans, and even Fishes ; for many of them—certain Orthocerata and Ammonites for example— afford evidence of gigantic dimensions. In the periods prior to the Chalk Formation, and at the time of its deposit, they were the agents employed for this purpose, and were succeeded in the Tertiary period by the Fossil Trachclipods, which are either entirely absent or very scarce iu the Secondary and Transitiou series, while the Fossil Cephalopods occur but rarely in the Tertiary beds. The extinct Ammonite [AmmoNrrEs], Baculite, Belemnite, Hamite, Orthoceratite, Turrilite, and Scaphite, will readily occur to the fossil zoologist as some of the ancient class. The Foraminifera, formerly placed by D'Orbigny in this class, are now no longer regarded even as Mailmen.