FISHE8 OF MINNESOTA. 7 



In the siin-fisli tlie pliarjngeal bones are similar to those of the 

 perch and in the identification of this group of fishes much depends 

 on the sharpness of the pharyngeal teeth and the manner in which 

 they are massed together. 



On the underside of the gill-flap, where the opercle joins the 

 preopercle, there are in some fishes a set of false gills called pscudo- 

 iJohranchia. In most of our fishes these are small or even absent, 

 but in a few chey are of family importance, viz., the Serranida3 or 

 Sea Bass, represented by our white bass, Roccus chrysops. 



The alimentary canal in the perch consists of the oesophagus, 

 stomach, small intestine and large intestine. The stomach, and, 

 in fact, the entire alimentary canal varies greatly in the dififer- 

 ent orders and families of fishes. In the perch the small 

 intestine leaves the stomach toward the latter's anterior end 

 and just at the beginning of the intestine there are three tube-like 

 appendages known as the Pijloric cceca (Fig. IV., P. C). In the 

 white-fish the pyloric cseca are very numerous and in some fishes 

 their number is one of the specific characters, viz., the wall-eyed 

 pikes (Stizostcdlon). It is generally considered that carniverous 

 fishes possess short intestines and herbiverous ones long intestines. 

 In certain minnows the length of the intestine is an important gen- 

 eric character, hence it is very often necessary to open the abdomen 

 and examine the intestine. In a minnow called the stone lugger 

 {Campostoma anomalum) the intestine is very long and coiled many 

 times around the air bladder. In a few fishes there is a spiral ar- 

 rangement in the intestine known as the spiral valve. 



The air-hladder is a sac, situated in the upper portion of the ab- 

 dominal cavity of fishes, which contains gases and which can be 

 compressed by the action of the muscles or allowed to expand and 

 thus regulate, in a measure, the specific gravity of the fish. In some 

 of the lower orders this air-bladder is cellular and connected by a 

 tube with the oesophagus and, it is supposed, can be used to some 

 extent as a lung; but in most of our fishes it is not connected with 

 the exterior and is not divided into more than two or three divi- 

 sions. Occasionally the number of the divisions in the air-bladder 

 is essential in determining the genus, and in this case the abdomina^ 

 cavity must be opened and the air-bladder examined 

 2 



