120 



THE ANIMAL KINGDOM. 



The fins of fishes are named according to their position, 

 which will be seen in the skeleton of a Perch (Fig. 79). 

 here a is the first Dorsal fin, and b the second, c the 

 Caudal, and d the Anal fin, e the Ventral, and / the 

 Pectoral (or chest) fin. 



An air-bladder is found in some fishes ; its exact use 

 is not quite ascertained, but it is evident that when the 

 ribs are contracted the quantity of air in the bladder is 

 diminished, and the fish becomes heavier ; that when the 

 bladder is again full the fish becomes lighter, and its 

 upward course is easier ; but fish swimming near the 

 bottom, as the Skate, Sole, &c., have no air-bladder. 



The skeleton of fishes is usually bony, but in many 

 cases it is formed of cartilage ; and this has led to their 

 being divided into 



Bony and Cartilaginous. 



Bony fishes are again divided into 



Spiny-finned and Soft-flnned. 



In the former (Fig. 81), the rays are stiff and bony, espe- 



Fig. 81. SPINY FIN. 



Fig. 82. SOFT FIN. 



cially in the dorsal fins; whilst in the latter (Fig. 82) they 

 arc soft. 



Amongst the spiny-finned fishes, the Perch, of which 

 the skeleton is shown in Fig. 79, is a well-known speci- 

 men, as it inhabits nearly all the streams and lakes in 

 England, and is found not only throughout Europe, but 

 also in Asia. It feeds on worms, insects, and small fishes, 



