FLIGHT. 



269 



compression or fill it by distension. Now it is ob- 

 vious that, by the effort to compress the swimming- 

 bladder, the body of the fish must be contracted, 

 and, consequently, as the absolute weight may be 



Swimming-Bladders. A, In the Dace : a, the stomach ; b, the 

 swimming-bladder. B, In the Conger Eel : a, the stomach ; 

 b 6, the swimming-bladder. 



considered the same, or, as the mathematicians say, 

 a constant quantity, the specific gravity, upon which 

 the buoyancy depends, must increase, and the fish 

 must accordingly sink. On the other hand, by the 

 effort to distend the swimming-bladder, the muscles 

 Z2 



