62 THE STORY OF FISH LIFE. 



— lie below and behind the pectorals ; and pro- 

 ject downwards from the ventral or under side 

 of the body. But the position of the pelvic or vent- 

 ral fins varies much. Thus, they may be seated 

 much further back than in the perch : as in the 

 salmon, for instance, where they lie in the middle 

 of the abdomen, behind the level of a line drawn 

 across the body from the base of the dorsal fins. They 

 are then said to be abdominal in position. In the 

 perch they are thoracic in position; that is to 

 say, they lie far forward in the region of the chest. 

 But in the burbot {Lota 'vulgaris) they actually 

 lie m front of the pectoral fins, and are then 

 said to be jugular in position (throat-fins) fig. 1, b. 

 But why this stress upon the jugular fins'? A 

 moment's reflection will show. If the pelvic fins 

 really correspond to the hind-limbs in higher 

 animals, then the hind-limbs in such a fish as the 

 present lie in front of the arms ! 



If the question were asked — What is the 

 function or use of the fins 1 probably the majority 

 would reply to swim with, as organs of locomotion 

 or rather propulsion. Well, this reply would be 

 partly, but only partly, true. The fins are 

 organs of locomotion ; but it is chiefly the tail 

 and caudal fin that serves this purpose : these 

 drive the fish forward by rapid and vigorous 

 strokes of the tail, which is lashed from side to 

 side alternately. When the fish is moving 

 slowly these movements can readily be seen. A 

 twist of the caudal fin alone is sufficient for gentle 

 forward movement, the fin working like the blade 

 of a screw. The pectoral fins serve, occasionally, 

 like the propellers of a ship when put full speed 



