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 interhemal 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 
