As relates to the internal structure of these conical organs, Eschricht ascertained that they are hollow, and that their cavities communi cate with the common cavity of the head : they have likewise their proper muscles, and each receives a large nerve derived imme diately from the anterior supra-cesophageal ganglion. As to the use of this elaborate apparatus, there is still room for speculation. Captain although he frequently ob served them porrected, while the creature was swimming, never saw them employed as suckers or instruments of prehension ; never theless, it seems impossible to doubt that such is their real office, when we reflect upon their remarkable structure, and further take into account their situation, so completely analo gous to that occupied by the sucking discs of the Cephalopoda, and still more closely re sembling the cephalic appendages of Pneumo derma. It is, therefore, extremely probable that these organs are employed for holding to foreign objects at the bottom of the sea, and that the great number of the sucking discs is in correspondence with the power possessed by the Clio of crawling about upon uneven surfaces.
The mouth of the Clio is a vertical fissure, that is easily displayed by slightly folding back the head-cones (fig. 110. 13, u). Its margins seem to enclose some calcareous substance, which, in specimens preserved in spirit, is of a chalky whiteness. Numerous muscular fasci culi surround this opening, which, when ex panded, has somewhat of a triangular form, so that during life the mouth can be forcibly opened by the radiating muscular fasciculi that surround it.
In the cavity of the mouth there may be observed, on each side, a round fossa, in which can be seen projecting, even with the naked eye, a hard shining substance, first noticed by Pallas and Fabricius, who re garded these bodies as simple teeth. Closer inspection, however, reveals them to have a very curious structure, which is, perhaps, unique, each consisting of a bundle of about thirty gold-coloured, crooked, stiff and sharp hooks (fig. 112. 22, w), derived from a common base (x), and forming a pair of lateral jaws, wherewith the creature seizes its food.
In the middle of the ventral aspect of the cavity of the mouth there is, moreover, a prominent tongue-shaped organ, which, when moderately magnified, may be seen to consist of two lateral bands of a black colour, which are united in the middle line, and which are covered with an immense number of extremely minute teeth, that will be more particularly described hereafter. The pharynx, when ex amined from above, is somewhat lyre-shaped : it is composed of two lateral branches (fig. 111. 19, i), the posterior ends of which are joined by a convex central portion (z). The tube of the cesophagus is not prolonged imme diately from its hinder extremity, but seems to arise from the hinder wall of the pharyngeal cavity (fig. 111. 17 and 21, e).
The nerves of the pharynx arise from two ganglia (fig. 111. 18, 20, y) situated imme diately behind it, in conjunction with the an terior ganglia of the circumcesophageal ring, and which inferiorly are connected together by strong branches of intercommunication and front which nerves radiate laterally to supply the surrounding parts. The thin ducts of the salivary glands (fig. 111. 17, 18, 19, and 20, g) terminate above these ganglia opening into the cavity of the mouth in the immediate vicinity of the tongue.
The pharynx, when viewed with a lens, and still more when examined under the micro scope, resembles, very closely, the gizzard of a gallinaceous bird, the resemblance consisting in the great strength of its muscular parietes.
Each lateral portion (fig. 111. 18, i) is a small curved cylinder, the outer wall of which is entirely muscular. The fasciculi are princi pally arranged in two layers, the fibres crossing each other. On opening one of these muscular capsules, by means of a fine pair of scissors it is found to contain, in its interior, a cylin drical body made up of several parts. At its anterior extremity are situated the lateral teeth above alluded to (fig. 111. 19, and fig.112. 22, v). These are arranged in parallel arches, in such a way that their points all attain the same height, notwithstanding the great difference in their length, the posterior (exterior) tooth (fig. 112. 23, a) being far the longest ; while the an terior (interior) (23, b) is the shortest of the series. The stem upon which these are fixed (22, w) is sloped off in the same pro portion, and has a somewhat triangular shape. When crushed under the microscope, it is found to consist entirely of muscular fibres ar ranged with considerable regularity, and prin cipally disposed in two opposite directions, so that they cross each other ; and doubtless a part of their office is to raise and depress the Individual teeth, implanted upon the common stem. The hinder portion of the cylinders (x) containing this extraordinary dental apparatus, is muscular, and composed of longitudinal fas eiculi, by the aid of which the stems that sup port the teeth are retracted, their protrusion being effected apparently by the construction of the capsules themselves. The manner in which the Clio makes use of these teeth may, therefore, be inferred from their anatomical arrangement. The cylinders wherein they are lodged are so much bent (fig. 111. IS, 19, i), that when the two dental organs of the oppo site sides are protruded the apices of the teeth with which they are armed must meet together outside the mouth, and when in this condition the teeth of each organ are widely separated and spread out, they will fbrm, as it were, a couple of long combs (19, v), and evidently perform the functions of a pair of tenacious jaws.