THEIR GENERAL CHARACTER AND STRUCTURE 19 



forming the distinction of Acanthopterygian (spiny-finned) 

 fishes, or they are soft, distinguishing Malacopterygian (soft- 

 finned fishes). Spinous rays are simple and jointless, sometimes 

 soft in substance, at other times stiff, bony, and sharp. Soft 

 rays are transversely articulate or jointed, either simple or 

 dividing into many branches. Not infrequently the jointing 

 is disguised by ossification ; but the magnifying glass serves 

 to distinguish such rays from true spines. Both kinds of rays 

 often occur in the same fin, but in that case the spinous rays are 

 invariably ranged in front of the others. Thus in the perch, 

 which carries the dorsal fin in two separate parts, the first 

 dorsal is supported by thirteen to fifteen spinous rays ; in the 

 second dorsal are two spinous rays in front, followed by twelve 

 or thirteen soft, jointed, and branched rays (Fig. I., 75). In 

 Malacopterygian fishes the foremost fin-ray is often stiff 

 and pointed, but it is not a true spine, and close examination 

 will reveal the jointing. Among British fresh-water fishes 

 there are some which have two rayed dorsal fins, such as 

 the perch, the burbot, the lamprey, and the miller's thumb ; 

 members of the Salmon Family invariably possess a rayed first 

 dorsal, and a small rudimentary second dorsal without rays, 

 called the adipose fin. The carps, loaches, pike, shad, and 

 sturgeon display but one rayed dorsal ; while in the stickle- 

 backs the place of the first dorsal is occupied by from three 

 to fifteen isolated sharp spines, without a connecting membrane, 

 behind which rises a bold second dorsal with from ten to twelve 

 soft rays. The anal fin is generally upon the same plan as 

 the dorsal fin, and, like that organ (Fig. I., 74), has its rays 

 connected with the ribs by interhasmal spines (Fig. I., 79). 



Little as the dorsal and anal fins have to do with propulsion, 

 except in such creatures as the eel, the flounder, and the 

 burbot, they are of great importance to locomotion. Deprived 

 of them, a fish moves in an uncertain, erratic manner ; they act 

 like the keel of a ship, keeping the animal on a straight course. 

 In a ship only the lower section is submerged a keel on deck 



