I36 A NATURAL HISTORY OF THE SEAS 



Related to the Puffer Fishes and Trunk Fishes is the 

 deep circular and much compressed Sun Fish or Head 

 Fish {Mold). In this fish the leathery body is so abbre- 

 viated behind that the impression given is that it has been 

 amputated just behind the dorsal and anal fins, which 

 appear as if attached to the head. Its generic name was 

 given to it by Linnaeus, who saw in the fish a resemblance 

 to a mill-wheel. The body of the fish is adapted for drift- 

 ing, but since certain deep-sea fishes have been found in 

 the interior of captured specimens, Sun Fish in all probabi- 

 lity periodically descend to great depth. 



In the Sea Horse {Hippocampus) the head and body is 

 suggestive of a knight of the chessboard. In these 

 fishes the powerful tail is prehensile and serves as an 

 efficient grappler. 



Fishes with elongated bodies are represented by the 

 Eels and Ribbon Fishes. 



Whilst the jaws and teeth of many fresh- water fishes 

 reach a high state of development as seen in the Pike 

 and the Brazilian Pirana, they show a much greater diversity 

 of form in sea fishes. They are the result of slow evolu- 

 tionary changes and the first primitive fishes were without 

 jaws in the true sense of the term, possessing merely 

 suctorial orifices similar to those which still obtain with 

 the Hag Fishes (Myxine) and Lampreys (Petromy^pri). 



The jaws of fishes are modifications of the branchial 

 arches and reach their highest development in the bony 

 fishes. Since many forms must often seize prey under 

 difficult circumstances, a large extensile mouth offers 

 many advantages, and in some fish the mouth can be shot 

 forward whilst at the same time widening to a remarkable 



