6o4 



KNOWLEDGE & SCIENTIFIC NEWS. 



[December, 1906. 



ing is, he thinks, probably a fair description of tlie 

 flyingf fish's methods in an ordinary flight : — 



1. The tail impelled and visibly wing assisted jump 

 from the water to a height where the wings can work 

 freely. 



2. The flight continued by an intensely rapid and 

 laboured wing-movement — one easily mistaken for still- 

 ness, and usually seen, if at all, as blurr. 



3. Short periods of slowing down of wing-speed, 

 during which the wing-movement becomes again 

 visible. (These are the "vibration" periods, repre- 

 senting to aeroplanists loose wing-trailing, or dragging 

 like a flapping flag — an impossibility.) These periods 

 often precede a special spurt such as is required to lift 

 the fish over an oncoming wave. 



4. Either sudden cessation of wing-movement and 

 consequent immediate drop into the sea, or a short slow 

 down into visibility (Xo. 3) previous to such drop. 



Diagram Indicating relat 



'■ It is to be noted that this vibration so often seen be- 

 fore the fish enters the water is one of the many pointers 

 to continuous wing-movement, for such a time is a 

 proper one for slowing down, but an absurd one for 

 renewal of wing-effort. Mr. .Adams has noticed the 

 vibration of the wings as being in "an almost horizon- 

 tal direction." This horizontal movement, if it exists, 

 as is probable, may afford, as I hope to show, a looked- 

 for key to the fish's action. .According to Pettigrew, 

 it is a necessity of flight, where wing-beats are in a 

 more or less vertical direction, that the up-beat should 

 meet with little and the down-beat with much resist- 

 ance from the air. This is arranged for in the case of 

 bats, birds, and certain insects by means of special 

 muscles and ligaments, which automatically flex the 

 wing for or during the up-stroke and extend it for or 

 during the down. Marey {Animal Mechanism, p. 263, 

 &'c. : Int. Science Series, 1893) equally recognises the 

 necessity for a diminished wing-area in the up-stroke, 

 but believes it to be obtained in birds through the 

 natural elasticity of the feathers, which enables them 

 to return to their ordinary position when the resistance 

 of the air in the down-stroke ceases to raise them. The 



flying fish's wing, as is known, is formed on quite a 

 different principle from that of a bird or bat. It opens 

 and closes somewhat like a fan. A partial automatic 

 closing of this fan at the foot of the downward stroke 

 in flight and opening at the top of the rising stroke 

 would both give the appearance of horizontal vibration 

 when seen either from above or below, and would turn 

 a somewhat difficult question of the mechanics of the 

 flight into a very simple one. Indeed, we have here 

 flying action on the same general principle as that 

 shown by Pettigrew and Marev to he necessarily pro- 

 vided for in the case of bats and birds, but the working 

 details of which are different and simpler, as becomes 

 a simpler form of wing. Perhaps that is the explana- 

 tion. There must, of course, be some explanation, and 

 that is not only the natural deduction from the peculiar 

 formation of the wing, but it also fits everything in. 

 The known (but indistinct) visibility of the larger rays 

 of the wings at times during flight points, perhaps, to 

 a comparative pause \yith wings full open before be- 

 ginning the down-stroke. Such pause would give the 

 open position, and with it the wing-tracery prominence. 

 The form of these fishes' wings points to this fan- 

 action rather than to other known horizontal wing- 

 actions of the nature of that of certain insects — the com- 

 mon fly, for instance." 



Lieut. -Col. Durnford adds to his paper a letter from 

 Mr. Burne, of the Roval College of Surgeons, who 

 dissected at the Museum the pectoral muscles of a flying 

 fish with those of a nearly related non-flying fish : — 

 " . . . . I have made a dissection of the pectoral 

 muscles of a flying fish (Exocoettis sp.) and of a nearly 

 related fish of much the same build, but without the 

 enlarged pectoral fins (Hcmiramphus). Both were speci- 

 mens from our store-room, and although in pretty good 

 condition had evidently been in spirit for a considerable 

 time. I enclose you tracings of the drawings I made. 

 The two of the external view were drawn with a 

 camera, and the Tlcmiramplim, which was rather less 

 in girth than the Exocrrius, was so much enlarged as to 

 have the same girth about an inch behind the pectorals. 

 I thought that body-girth sufficiently far behind the fins 

 not to be influenced bv their degree of development was 

 the best standard of size to take — better than length, 

 for instance. As a matter of fact, the fish were very 

 much the same length, the Exoaetits being rather the 

 longer. 



" The drawings, I think, explain themselves. The 

 flying fish muscles w'cre, as you see, considerably larger, 

 both in area and in thickness, than in Hcmiramphus, 

 and the same was the case with the muscles on the 

 deep surface of the fin. In their arrangement they 

 were much the same in both fish and the same as in 

 other bony fishes (the cod, for instance). The numbers 

 on the surface of the fins are the points where I took 

 the thickness of the muscle bv plunging a needle into 

 it and measuring the depth to which the needle entered. 

 You will notice the great length of the muscles in 

 Exocceius — a long muscle means a proportionate length 

 of contraction. 



" . . . . there is a very marked difference in the 

 size of the muscles of these two fishes. . . ." 



"This tracing," observes Lieut. -Col. Durnford, "gives 

 about 44 times greater bulk of muscle to the Exccatus 

 than to the Hcmiramphus.^'' With this light it will not be 

 out of place to requote and amplify the one " proof." dis- 

 tinguishing the addition by italics : — " The pectoral 

 muscles of birds depressing their wings weigh on an 

 average one-sixth the total weight of their body, the 

 pectoral muscles of bats one-thirteenth, the muscles of 



