THE VERTEBRATES 197 



in arctic and subarctic seas. The herring, soft and weak 

 in body, are more numerous in individuals than any other 

 fishes. The flounders, of many kinds, lie flat on the sea 

 bottom. They have the head so twisted that the two eyes 

 occur both together on the uppermost side (fig. 97). The 

 members of the great mackerel tribe swim in the open sea, 



FIG. 97. The winter flounder, Pseudopleuronectes americanus. (After 

 Goode.) 



often in great schools. Largest and swiftest of these is 

 the swordfish, in which the whole upper jaw is grown to- 

 gether to form a long bony sword, a weap@n of offense that 

 can pierce the wooden bottom of a boat. 



Many of the ocean fishes are of strange form and ap- 

 pearance. The sea-horses (fig. 98) are odd fishes, cov- 

 ered with a bony shell, and with the head shaped like that 

 of a 'horse. They are little fishes, rarely a foot long, and 

 cling by their curved tails to floating seaweed. The por- 

 cupine fishes and swell fishes have the power of filling the 

 stomach with air, which they gulp from the surface. They 

 can escape from their pursuers by floating as a round spiny 

 ball on the surface. The flying fishes leap out of the water, 

 and sail for long distances through the air like grasshoppers. 

 They cannot flap their long pectoral fins, and do not truly 



