CI303] 
are but as it were inverted Lungs, and are of the fame 
ufe to Fiflies as Lungs to Quadrupeds: that the whole 
Ina^s of blood in every Circulation paffes through the 
Gills, as in Quadrupeds it do's through the Lungs ; 
only it returns not again to the heart , and there- 
fore in Fiflies as well the VelTels that carry it to the 
Gills, asthofe that bring it back, are Arteries. It isal- 
fo proved, that fiflies have a kind of refpiration, as well 
as Land Animals^ and that the ufe of the Air is as necef- 
fary to thofe as thefe ; fo that if it be intercluded, or 
made any ways unfit for life, they cannot live, as is clear- 
ly evidenced by great variety of undoubted experiments. 
The fins ferve not {o much for progrefCve motion, as 
for holding the body eredt, and for moving it to and 
fro, upwards and downwards in the water : the pro=» 
greffion is performed principally by the motion of the 
Tail, bythefudden extenfion whereof being infle(Sted, 
the Fifh flioots it felf forward with great force and Ve- 
locity. Vid. Phil. Tranf: N, iif. 
The fwimming-bladders found in mofl fiflies, ferve 
to bring the body to an iEquilibrium with the Element 
wherein it fwims, that fo it may with more facility be 
impelled or moved any way. That this is one ufe of 
it, is demonftrated from experience, for upon break- 
ing the faid Bladder, the fifli is no longer able to fup- 
port it felf in the water, but prefently finks down, and 
conftantly lies groveling at the bottom, from this Air-^ 
bladder there is a Ghannell or paffage in mofl fiflies, 
leading to the mouth of the Stomack, butinfomefew 
to the bottom of it, and there terminated: which pro- 
bably ferves for the emiflSon and reception of Air at / 
pleafurea to ballance the body according as either its/ 
gravity, or that of the Medium is altered. It is alfo^ 
probable that the fifli hath a power of contradting aq/i 
dilating this VefTel, either by fome mufcular force ifh- 
herent in its Coats, or by the help of fome externall 
B b b b adja- 
