38 



MARKETABLE BRITISH MARINE FISHES 



expand and contract regularly while the fish is alive. There is 

 also usually a smaller opening from the throat, known as the 

 spiracle, and situated just behind the eye. Another peculiarity 

 of these fishes is the position of the mouth, which is a wide 

 transverse slit on the flat, lower surface of the head. In other 

 words, the snout projects usually to some distance beyond the 

 jaws and terminates in a point. The fin-rays in these fishes are 

 rods of gristle or cartilage with very numerous joints, and in 

 addition to these there is beneath the skin of the fins a layer 

 of fine horny fibres. The second pair of side fins or pelvic fins 

 are always placed close to the vent. The tail has a characteristic 

 form, consisting of two unequal lobes, of which the upper is the 

 longer : the spinal column is bent up at the base of the tail, and 

 continued into the upper lobe. 



Fig. 3. — The Bass, as example of the bony fishes. D.F. dorsal fin; V. F. ventral 

 fin; C.F. caudal fin; Pc. F. pectoral fin; Pv. F. pelvic fin; L. L. lateral 

 line ; G.C. gill-cover ; N. nostrils of right side. 



Bones and scales are the chief characteristics of the scaly 

 fishes, although in some the scales are almost or entirely absent, 

 as for instance in the eel. The scales overlap one another like 

 the tiles of a house, and the larger part of each is imbedded in 

 the skin, only the smaller hinder portion being exposed. The 

 tube of the lateral line pierces a longitudinal series of special 

 scales, and to each of these scales corresponds a pore open- 

 ing into the interior of the tube. The mouth is usually at the 

 end of the snout and provided with bony jaws and teeth. The 

 gill-cover, a broad plate on each side behind the head supported 

 by bone, covers over the chamber in which the gills are contained 



