(1763). Cuvier justly observes that, whatever opinions may be entertained relative to the use of the air-bladder, it is difficult to explain how so considerable an organ has been refused to so many fishes - not only to those which ordinarily remain quiet at the bottom of the water, as Skates and Plat-fishes, but to many others that apparently yield to none either in the rapidity or facility of their movements, such as the Mackerel for instance; yet even while the common Mackerel (Scomber scomber) has no air-bladder, a very nearly allied species (Scomber pneu-matophorus) is provided with one; and of this many other instances might be adduced.

(1764). From the circumstances under which fishes seize and swallow their prey, it must be evident that they are incapable of enjoying any very refined sense of taste. Those species which are carnivorous are of necessity compelled to catch with their teeth, and thus retain a firm hold of the active and slippery food they are destined to devour. To divide or masticate theuvaliment would be impracticable; and even were they permitted so to do, the water which perpetually washes through the interior of their mouths would obviously preclude the possibility of appreciating savours. In the construction of the mouth of a fish we therefore find, generally speaking, that every part has been made subservient to prehension: teeth, sometimes in the form of delicate spines, or else presenting the appearance of sharp recurved hooks, have been fixed in every possible situation where they could be made available as prehensile organs: not only are the jaws densely studded with these penetrating points, but they are occasionally placed on every bone which surrounds the oral cavity or supports the entrance of the pharynx.

The intermaxillary, the maxillary, and the palatine bones, the vomer, the branchial arches, the pharyngeal bones, and even the tongue itself, may all support a dental apparatus, either of the same description or composed of teeth of different shapes; generally, however, some of these bones are unarmed, and occasionally teeth of any kind are altogether wanting.

(1765). But if such is the most usual arrangement of the dental apparatus in fishes, we must be prepared to find, in a class so extensive as that we are now investigating, various modifications both in the form and arrangement of the teeth, adapting them to the diverse habits and necessities of individual species; and a few of these we must not omit to notice in this place.

* "Sull' analisi dell' aria contenuta nella vescica natatoria dei Pesci." Pavia, 1809, 4to.

(1766). The Myxine, or Hag-fish, one of the lowest of the entire class, possesses no osseous framework to which teeth could he attached; and yet, from the parasitical life which this creature leads, it has need of dental organs of considerable efficiency. The Myxine, feeble and helpless as the casual observer might suppose it, is in reality one of the most formidable assailants with which the larger fishes have to contend, since neither strength nor activity avail aught in defending them against a foe apparently so despicable. Fixing its mouth firmly to the skin of its comparatively gigantic victim, the Myxine bores its way into its flesh by means of a dental apparatus of a very extraordinary description. A single fang-like tooth is fixed to the median line of the palate, and the tongue is armed on each side with two horny plates deeply serrated: thus provided, the Myxine, when it attacks its prey, plunges its palatine hook into its flesh; and thus securing a firm hold, the lingual saws, aided by the suctorial action of the mouth, tear their way to its very vitals*.

(1767). In the Lamprey the whole interior of the mouth is studded with horny teeth, not merely fixed to the palate and tongue, but to the cartilaginous representative of the inferior maxilla and to the inner surface of the lips.

(1768). In the Carp tribe (Cyprinidce) the jaws are destitute of teeth; but in the throat there is a singular apparatus serving for the mastication of their food. The basilar bone at the base of the skull supports a broad three-sided dental plate, which might be compared to an anvil; while the two inferior pharyngeal bones are each armed with four or five large teeth, so disposed that, by working upon the piece first mentioned, they bruise and triturate the aliment before it is permitted to pass into the digestive cavity.

(1769). In Skates (Raidae) the internal surface both of the upper and lower jaws is so covered with teeth, that they have the appearance of a tessellated pavement: these teeth are sometimes flat and smooth, so as to be merely useful in crushing prey; but in many species they are prolonged into sharp hooks adapted to prehension.

(1770). In Sharks a beautiful provision is met with. Several rows of teeth placed one behind the other are found laid flat, and concealed behind the jaw. One row only, composed of triangular cutting teeth, stands erect and ready for use; but when these fall off, blunted and unfit for service, the next row rises to take their place; and thus a succession of efficient weapons are given to these terrific monsters of the ocean.

* Professor Owen,' Odontography; or a Treatise on the Comparative Anatomy of the Teeth, their Physiological Relations, Mode of Development, and Microscopic Structure,' etc. 4to. Bailliere, 1840.

(1771). We will not enlarge further upon this portion of our subject; enough has been said for our present purpose, and the reader will find elsewhere abundant information*.

(1772). The teeth of osseous fishes are generally firmly anchylosed to the bones that support them, although in a few instances they are found fixed in sockets, as in the rostral teeth of the Saw-fish (Pristis), and in the mouth of Sphyrcena, Acanthurus, Dictyodus, etc.1 But there are other modes of attachment only met with among fishes, some of which are not a little curious; and Professor Owen, in his truly splendid work above referred to, thus describes the most important: -