DIGESTIVE SYSTEM.—The animals which we have thus seen to be endowed. with so various and formidable means for seizing and over coming the struggles of a living prey are pro vided with adequate weapons for completing its destruction, and preparing it for deglutition. These consist of a pair of strong, sharp, hooked mandibles, which are of a horny texture in the Dibranchiate Cephalopod, (a, b, .fig. 218,) where they are fitted for cutting and tearing the softer animals which they are enabled to catch ; but are strengthened by a dense calcareous sub stance in the Nautilus, (a, b, fig. 217,) which, from its more limited sphere of action, is pro bably restricted in reg,ard to food to such crus taceous and testaceous animals as it may sur prise by stealth, and whose defensive armour it is thus enabled to break up.* The mandibles, which are hollow sheaths, like the horny covering of the beak of a Bird or Tortoise, are fixed upon a firm fleshy sub stance, (c, c, .fig. 2170 which resembles the animal part of bone after the earth has been removed by means of an acid. At the base of the mandibles the fibrous structure of this part becomes apparent, and a strong stratum, (g, .fig. 217,) passing between the bases of the mandibles, serves for their divarication ; their closure is effected by fasciculi of muscular fibres, which surround them externally near the reflection of the circular lip. When the mouth is closed, the lower mandible (b) over laps the upper (a).
The oral aperture is in the centre of the base of the feet, and appears in the form of a small circular orifice, formed by the contracted fleshy lip which surrounds and more or less conceals the mandibles.
In the Nautilus the margin of the lip (c) is beset with several rows of elongated papillw, irregularly disposed ; external to which are the labial processes with their tentacles : these, in the specimen we dissected, com pletely overlapped and concealed the oral ap paratus.
In the Calamaries the jaws are surrounded, external to the fringed circular lip, by a thin membrane, which is produced into short pyra midal processes, corresponding in number to the eight feet, and supporting minute rudimen tal suckers ; - thus imitating the external feet, as the labial processes of the Nautilus repeat the structure of the digital processes. In the genus Sepioteuthis the circular lip immediate!y surrounding the jaws is tumid and plicated, but not papillose ; external to it are two cir cular ridges of membrane, then a thin mem brane with jagged margins, and lastly a mem brane with its margin produced into eight angular processes, which are not, however, free, as in Loligo, but are tied down in the interspaces of the eight legs ; small rudimental suckers may be observed on these processes.
In Onychoteuthis the inner lip (d, fig. 218) is tumid, and merely subplicated ; the angles of the external labial membrane are extended along the middle of each foot for a short dis tance. In Sepia the inner lip is fringed, as in Nautilus. The outer lip is tied down by mus cular bands to the bases of the arms, but sends forward eight short, conical, unarmed processes. In Loligopsis and Cranchia the outer-lip sends off a muscular band to the base of each arm, but has no free processes. In Octopus the suckers commence immediately round the mar gin of the oral aperture, which is so con tracted that the mandibles can seldom be seen without dissection : the inner-lip is fimbriated, as in Sepia. In Ocytha it is tumid and entire, but pli cated both circularly and transversely.
The tongue is a large and complicated organ, and is constructed on the same plan in both orders of Cephalopods. In the Nau tilus it is supported by an oblong horny transversely striated substance, which appears to represent the body of an os hyoides (a, fig. 236.) The posterior ex tremity of this substance is free, or connected only by a few filaments with the parts above, but its anterior extremity is embraced by a pair of retractor muscles (b), vvhich originate from the posterior margins of the lower mandible. The fleshy substance of the tongue, thus supported, is produced ante riorly, and forms three caruncles (c), very soft in texture, and beset with numerous papillT, having all the characters of a perfect organ of taste. The anterior or terminal caruncle is the largest, and four delicate retractor or depressor muscles (d) are inserted into it. Behind the caruncles the dorsum of the tongue is encased with a thin layer of horny matter, about five lines in length, from which arise four longitu dinal rows of slender prickles (e), which are from one to two lines in length, and are in curvated backwards. The number of these prickles is twelve in each row, singularly cor responding with the number of tentacles given off from the labial processes.