II.—FLYING-FISHES.
The motions of animals vary greatly with reference to the medium in which they live. Our present knowledge renders it, however, necessary that we should weigh these differences with reference to the structural character of the organs of locomotion themselves, as well as to that of the peculiar resistance of the element in which they move. When we speak of the flight of Birds, of Insects, of Fishes, of Bats, &c., and designate their locomotive organs indiscriminately as wings, it is evident that the character of the motion and not the special structure of the organs has determined our nomenclature. We are influenced by the same consideration when we give the name of fins to the organs of all animals which swim in the water, be they Whales, Turtles, Fishes, Crustacea, or Mollusks. It requires but a superficial acquaintance with the anatomy of the flying-fishes to perceive that their organs of flight are built upon exactly the same pattern as the pectoral fins of most fishes, and differ entirely from the wing of birds, as also from the wing of bats, the latter being in all essentials a paw, identical with the paw of ordinary quadrupeds, save the length of the fingers and the absence of nails on the longest of them. No wonder, then, that the flight of the flying-fishes should entirely differ from that of birds or bats.
I have had frequent occasions to observe the flying-fishes attentively. I am confident not only that they change the direction of their flight, but that they raise or lower their line of movement repeatedly, without returning to the water. I avoid the word falling designedly, for all the acts of these fishes during their flight seem to me completely voluntary. They raise themselves from the surface of the water by rapidly repeated blows with the tail, and more than once have I seen them descend again to the surface of the water in order to repeat this movement; thus renewing 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 movement. 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 perfectly 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 amplitude 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 they move.
The most common flying-fishes of the Atlantic belong to the genus Exocetus, and are closely allied to our Billfish (Belone). J. Müller has shown that they differ greatly from the Herrings, with which they were formerly associated, and should form a distinct family, to which he has given the name of Scomberesoces. The other flying-fishes belong to the family of the Cottoids, of which our common Sculpins are the chief representatives.