An introduction to the study of fishes

by Albert C. L. G. Günther

Fig. 56.—Siphonal Stomach and Pyloric Appendages of a Female Salmon, 3⅓ feet long. a a a, Pyloric appendages; ch, ductus choledochus; oe, œsophagus; st, lower end of stomach; p, pyloric region; i, ascending; and í’, descending portion of intestine.

The duodenum receives always the hepatic and pancreatic secretions, and, besides, those of the appendices pyloricæ, which, in varying numbers (from 1 to 200), are of very common occurrence in Teleosteans (Fig. [56]). They vary also in length and width, and whilst the narrowest serve only as secretory organs, the widest are frequently found filled with the same contents as the intestine. When few in number, each opens by a separate duct into the duodenum; when their number is greater two or more coalesce into a common duct; in the latter case the appendages cease to be free, and are connected with one another by a more or less firm tissue.

Cœcal appendages at the end of the intestinal tract are of exceedingly rare occurrence in fishes (Box). There is no cloaca in Teleosteans.

In the majority of Teleosteous fishes the vent is situated on the boundary between trunk and tail, behind the ventral fins. In a few it lies farther backwards, not far from the caudal fin; more frequently it is advanced forwards, under the middle of the abdomen or to the scapular arch. In two fishes, Aphredoderus and Amblyopsis, it lies before the pectoral fins.

A peritoneum envelops all the divisions of the intestinal tract within the abdominal cavity. A broad, well-developed omentum has hitherto been found in Gobiesox cephalus only.

Liver.—The existence of a liver in Branchiostoma as a long diverticulum of the intestine has been mentioned above. In the Myxinoids the liver is divided into two glandular bodies, an anterior rounded smaller one, and a posterior larger one of an elongate shape. The gall-bladder lies between both, and receives a cystic duct from each of them. In the other fishes the proportionally large liver is a single large gland, from which only now and then small portions are found to be detached. It is either simple, or with a right and left lobe, or with a third lobe in the middle; each lobe may have incisions or subdivisions, which, however, are very inconstant. The liver of fishes is distinguished by the great quantity of fluid fat (oil) which it contains. The gall-bladder is but rarely absent, and attached to the right lobe, or towards the centre; however, in some fishes it is detached from the liver and connected with it by the cystic duct only. The bile may be conveyed by one or more hepatic ducts into a common duct which is continued towards the gall-bladder as ductus cysticus, and towards the duodenum as ductus choledochus; or some of the hepatic ducts enter directly the gall-bladder, or directly the duodenum, without communicating with the common duct. Individual variations in this respect are of common occurrence.

A pancreas has been found hitherto in all Chondropterygians, Acipenser, and many Teleosteans. In the first it is a glandular mass of considerable size behind the stomach, close to the spleen; its duct leads into the duodenum. In the Sturgeons the pancreas is attached to the duodenum, and opens close to the ductus choledochus. In Silurus glanis it is very large, and the ductus choledochus passes through its substance; it is smaller in Belone and Pleuronectes, and situated in the mesentery; its duct accompanies the terminal portion of the ductus choledochus. In the Salmon, which possesses a large lobed pancreas, the duct is so intimately connected with the ductus choledochus that both appear externally as a single duct only.

The spleen, which is substantially a lymphatic gland, may be mentioned here, as it is constantly situated in the immediate vicinity of the stomach, generally near its cardiac portion. With the exception of Branchiostoma, it is found in all fishes, and appears as a rounded or oblong organ of dark-red colour. In the Sharks frequently one or more smaller pieces are detached from the principal body. In the Dipnoi a thin layer of a very soft substance of brownish-black colour below the mucous membrane of the stomach and upper part of the intestine has been regarded as the homologue of the spleen (Fig. [57], m). In most Teleostei the spleen is undivided, and appended by its vessels and a fold of the peritoneum to the pyloric bend of the stomach or the beginning of the intestine.

Fig. 57.—Upper part of Intestine of Ceratodus. The anterior wall of the intestine is opened, the liver (c) and gall-bladder (e) being drawn forward. A slit is made at n, through which part of the next compartment of the spirally wound intestine may be seen.