The carnivorous genera, whether marine (_e.g._ _Conus_, _Murex_, _Buccinum_, _Nassa_) or land (_e.g._ _Testacella_, _Glandina_, _Streptaxis_, _Ennea_), are entirely destitute of jaws, the reason probably being that in all these cases the teeth of the radula are sufficiently powerful to do the work of tearing up the food without the aid of a masticatory organ as well. Jaws are also wanting in the Heteropoda, and in many of the Nudibranchiata and Tectibranchiata. In the Cephalopoda the jaws, or ‘beaks,’ as they are called, are most formidable weapons of attack. In shape they closely resemble the beaks of a parrot, but the hook on the dorsal side of the mouth does not, as in birds, close over the lower hook, but fits under it. Powerful muscles govern these mandibles, which must operate with immense effect upon their prey (Fig. 110). [Illustration: FIG. 110.--Jaws of _Sepia_: =A=, _in situ_ within the buccal mass, several of the arms having been cut away; =B=, removed from the mouth and slightly enlarged.] [Illustration: FIG. 111.--_Patella vulgata_ L., showing the normal position of the radula, which is doubled back in a bow; the shell has been removed, and the whole visceral mass is turned forward, exposing the dorsal surface of the muscular foot: _gr_, longitudinal groove on this surface; _i_, _i_, intestine; _l_, liver; _m_, _m_, mantle edge; _mu_, muscles (cut through) fastening the visceral mass to the upper sides of the foot; _ov_, ovary; _r_, radula; _u.f_, upper or dorsal surface of the foot.] _The Radula._[322]--When the food has passed beyond the operation of the jaw, it comes within the province of the radula, the front part of which perhaps co-operates to a certain extent with the jaw in performing the biting process. The function of the radula as a whole is to tear or scratch, not to bite; the food passes over it and is carded small, the effect being very much the same as if, instead of dragging a harrow over the surface of a field, we were to turn the harrow points upwards, and then drag the field over the harrow. The radula itself is a band or ribbon of varying length and breadth, formed of chitin, generally almost transparent, sometimes beautifully coloured, especially at the front end, with red or yellow.[323] It lies enveloped in a kind of membrane, in the floor of the mouth and throat, being quite flat in the forward part, but usually curving up so as to line the sides of the throat farther back, and in some cases eventually forming almost a tube. The upper surface, _i.e._ the surface over which the food passes, is covered with teeth of the most varied shape, size, number, and disposition, which are almost invariably arranged in symmetrical rows. These teeth are attached to the cartilage on which they work by muscles which serve to erect or depress them; probably also the radula as a whole can be given a forward or backward motion, so as to rasp or card the substances which pass over it.