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; 4, the 
swimming-bladder. — FB In the Conger Eel: a, the stomach ; 
6 b, 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 soi imei, the muscles 
