16 THE COMMERCIAL SEA FISHES OF 



It is thus that in fishes economy of space is effected by 

 an increase of the secreting and absorbing surface of 

 the vasculo-mucous membrane lining the intestinal tract, 

 whether such be merely raised into puckers, or those 

 puckers be continued into transverse folds, or even form- 

 'ing a circular, uninterrupted spiral valve or coil to the 

 large intestines. 



In many fishes we find what are termed csecal or pyloric 

 appendages, situated at the commencement of the small 

 intestines. Some have held these appendages to be lateral 

 prolongations of the intestine, which pour out a secretion 

 similar to that of the intestinal mucous membrane. Others 

 consider them as a modified form of pancreas, notwith- 

 standing that a rudimentary pancreatic gland has been 

 detected in the form of a minute glandular body, ter- 

 minating in a duct, which opens by from one to three 

 orifices into the intestines close to the bile duct. It is seen 

 both in fishes which possess pyloric appendages, as the 

 perch, cod, salmon, and sturgeon, as well as in such as are 

 deficient in them, as the brama, gar-pike, and pike, while 

 the sharks and rays are furnished with a reddish-yellow 

 and lobulated gland, which is more similar to what is per- 

 ceived in the higher forms of vertebrate animals. 



In osseous fishes these pancreatic ducts are seen as one 

 or more small tubes, each ending externally in a blind 

 extremity. They either surround the commencement of 

 the small intestine, or spring from one of its sides in the 

 first portion of its course, and each opening internally into 

 it. A single fish may possess from one to a hundred or 

 more of these appendages. In the sword-fish (Xiphias) 

 all the various tubes conjoin. In the sturgeon (Acipenser) 

 a mass of areolar tissue binds the various caeca together, 

 forming it into a pa enchymatous conglomerate gland. 



