APPENDIX. 



523 



surface of the water in order to repeat this movement ; thus renew- 

 ing the impulse and enabling themselves to continue for a longer 

 time their passage through the air. Their changes of direction, 

 either to the right and left or in rising and descending, are not due 

 to the beating of the wings, that is to say, of the great pectoral fins, 

 but simply to an inflexion of the whole surface, in one or the other 

 direction, by the contraction of the muscles controlling the action 

 of the fin-rays, their pressure against the air determining the move- 

 ment. The flying-fish is in fact a living shuttlecock, capable of 

 directing its own course by the bending of its large fins. It probably 

 maintains itself in the air until the necessity of breathing compels 

 it to return to the water. The motive of its flight seems to me to 

 be fear ; for it is always in the immediate neighborhood and in front 

 of the vessel that they are seen to rise ; or perhaps at a distance 

 when they are pursued by some large fish. Now that I have studied 

 their movements, I am better able to appreciate the peculiarities of 

 their structure, especially the inequality of the caudal fin. It is per- 

 fectly clear that the greater length of the lower lobe of the caudal 

 is intended to facilitate the movements by which the whole body is 

 thrown out of water and carried through the air ; while the ampli- 

 tude of the pectoral fins affords only a support during the passage 

 through the lighter medium. Nothing shows more plainly the 

 freedom of their movements than the fact that, when the surface 

 of the sea is swelling into billows, the flying-fishes may hug its 

 inequalities very closely and do not move in a regular curve, first 

 ascending from and then descending again to the level of the 

 water. Nor do they appear to fall into their natural element, as 

 if the power that had impelled them was exhausted ; they seem 

 rather to dive voluntarily into the water, sometimes after a very 

 short and sometimes after a rather protracted flight, during which 

 they may change their direction, as well as the height at which 

 Ihey move. 



The most common flying-fishes of the Atlantic belong to the 

 genus Exocetus, and are closely allied to our Billfish (Belone). 



