There appears to be one example in the Dibranchiate Order where the liver is divided. into four lobes, as in the Nautilus ; this occurs, according to Dr. Grant, in the Loligopsis guttata ; but in the figure which is given of this structure the lobes are each distinct from the rest, and divided at the middle line ; vvhile in the Nautilus the four lobes are united together. Rathke, on the contrary, who has given an elaborate account of the Anatomy of Loligopsis under the name of Perothis,* describes and delineates the liver, in the two species of that genus dissected by him, as a simple undivided viscus, of an ellip soid figure, situated in the middle line of the body (12,fig. 223). In Onychoteuthis Banksii the liver is a single elongated laterally com pressed lobe, obtuse and undivided at both extremities. In the Sagittated Calamary it is single, elongated, and cylindrical. In Sepia and Rossia it is divided into two lateral lobes, both of which are notched at the upper extre mity. In the Argonaut the two lobes are united for a considerable extent along the mesial line, but are greatly produced laterally, and advance forw ards, narrowing towards a point, so as partially to enclose the alimentary canal. In Octopus the liver is a single oval mass, flattened anteriorly. In Eledone it pre sents a spherical form, corresponding to the ventricose form of the visceral sac. In the two latter genera the ink-bag is enclosed within the capsule of the liver, but in the Argonaut and in all the Decapodous genera this is not the case.
The proper capsule of the liver is very delicate, and apparently nothing more than the outer ter mination of the cellular tissue which connects the lobules of its parenchyma. When this is inflated from the biliary ducts, it is seen to be composed of cells, formed by the ulti mate ramifications of the duct, with very thin parietes, and re latively larger than those of the liver of the Snail. This is the structure observable in the liver of the Octopus, according to Muller,* and Rathke observed the same structure in the terminal cceca of the hepatic duct in Loligopsis.
In the Octopo dous Dibranchiates, which have a large.
crop, and the lower pair of salivary glands of corres pondingly large di mensions, the two biliary ducts are simple canals, which are continued from the lower end of the liver, embracing the origin of the intes tine, and uniting be low - it to terminate . by a common orifice in the pyloric ap pendage. But in the Decapodous tribe they continue to send off branches, which subdivide and form clusters of ccecal appendages, through a greater or less proportion of their entire course. The follicles thus appended to the biliary ducts are larger than those vvhich form the liver ; they are figured by Monro in the Loligo sagittata as the ovary, but were considered by Mr. Hunter to represent the pancreas in the Cuttle fish, from which species he took the preparation of these parts in his collection.t These folli cles are described with much care and detail by Ratlike in the genus Loligopsis, and, ac cording to him, in one species (10, fig. 223), ( Lol. Eschscholtzii,) they terminate, not in the hepatic duct, but separately and directly in the pyloric appendage. We have found these cystic follicles appended to the hepatic duct in Sepiola, Onychoteuthis, Sepioteuthis, and in the genus Rossia, in vvhich they present the largest proportional development hitherto ob served in the class. Here the biliary ducts, as
soon a:s they emerge from the liver, branch out into an arborescent mass of larger and more elongated follicles than those constituting the hepatic parenchyma; these ramifications extend full half an inch from the hepatic duct, and conceal the upper halves of both the stomach and pyloric appendage.
Organs of Circulation.— Prior to the dis section of the Nautilus Pompilius the Ce phalopods were regarded as having three dis tinct hearts, a. peculiarity which is not found in the circulating system of any other class of animals. In the Nautilus, however, there is but one ventricle, which is systemic, as in the inferior Mollusks; and the three hearts are, therefore, characteristic only of the Dibran chiate or higher order of Cephalopods.
These differences in the circulating system of the two orders are accompanied with equally well marked modifications of the respiratory organs; and hence the primary divisions of the class are each distinguished by characters of equal value, and derived from modifications of those organs which afford the most natural indica tions of the corresponding groups in the other classes of the Molluscous division of Inverte brate animals.
In the Nautilus the veins vvhich return the blood from the labial and digital tentacles and adjacent parts of the head and mouth, termi nate in the sinus excavated in the substance of the cephalic cartilage. From this sinus the great anterior vena cava (a, fig. 224) is continued, running in the interspace of the shell-muscles on the ventral aspect of the abdominal cavity, and terminating in a sinus (b) just within the pericardium, where it receives the venous trunks of the viscera. (These are indicated by bristles in the figure.) The structure of the vena cava is very remark able ; it is of a flattened form, being included be tween a strong membrane on the lower or ventral aspect, and a layer of transverse muscular fibres, which decussate each other on the upper or dorsal aspect; both the membrane and the muscle pass across from the inferior margin of one shell-muscle to the other ; they consequently increase in breadth as those muscles diverge, and complete the parietes of the abdomen on the ventral aspect. The vein, however, main tains a more uniform calibre by its proper internal coat, leaving a space on either side between the membrane and muscle. The ad hesion of the proper membrane to the muscular fibres is very strong, and these, though ex trinsic to the vessel, form part of its parietes on the dorsal aspect. There are several small intervals left between the muscular fibres and corresponding round apertures (a') in the mem brane of the vein and contiguous peritoneum, by which the latter membrane becomes continuous with the lining membrane of the vein : from this structure it would seem that the blood might floi,v into the peritoneal cavity, or the fluid contents of that cavity be absorbed into the vein.* In the structure of the other veins of the Nautilus nothing uncommon is observed : their principal termination is in the sinus above-mentioned, where the greater or systemic circulation ceases, if we are to consider the lesser circulation to commence where the blood again begins to move from trunks to branches.