OF FISHES IN GENERAL. 
9 
"Karel, fillies can, by extending thefe, flop their motion, 
and produce tnora ;and, when fwimming in a ftreight di- 
rection, they can, by folding either, while the other 
continues to ply, dired their motion to that fide. The 
foe of thefe fins, is, in general, proportioned to that of 
f be head of the fill to which they belong ; and it is 
probably one ufe of them, to prevent the fifb from be- 
mg overbalanced by the weight of its head, and pre- 
cipitated to the bottom. In fome fifties, the pectoral fins 
ferve the fame purpofe as the wings of birds ; for, by 
their means, they are enabled to rife from their watery 
element, and to fly for a confiderable fpace, till their fins 
be fo diied by the air, that, in fpite of every exertion, 
they again link into the water. 
A fiih completely equipped for fwimming, has fevea 
fins, two pairs, and three fmgle ones ; and of the latter, 
two are above, and one below : But, fince thofe which 
have the greateft number cf fins, are not the fwifteft, it 
has been concluded, that the tail is the principal caufe of 
>.he fwiitnefs of a filli’s motion. When in purfuit of its 
prey, or avoiding an enemy, all the fmaller fins are laid 
clofe to its body ; then, by the impulfe of the tail alone, 
Hlkims through the water with the incredible velocity of 
a dait 01 an arrow* The mufcles, by which the tail 
3S moved > are, by far, the thickeft and ftrongeft of the 
bole body ; arid to give diredion to the great impetus 
ich they communicate to the fiih, feems to be the chief 
purpofe of all the fmaller fins. 
m ot,on of fifties, is fuppofed to be aflifted by the 
* !n ° bladder, which, by contradion and dilatation, 
, r 1 a ^ c or fink them in the watery element at 
e j and, as that element is of very different degrees 
Vot ' "*• E ot 
WiUoubii Ichthyol. p. 4 . 
