84? ANGLING. 



in quantity in proportion to the depth at which the 

 species dwells. Carus considers it probable that 

 the vessel in question performs a part analogous to 

 that of the expiratory functions of the lungs in the 

 higher classes, by not only separating excrementi- 

 tious azote, and superabundant oxygen, from the 

 blood, but even discharging those elements in such 

 species as have this particular viscus provided with 

 an air-duct. 



The more obvious uses, however, of this organ, 

 seem to be to maintain the fish in equilibrium, and 

 to lighten or increase the relative weight, so as to 

 cause a sinking or ascension in proportion as the 

 bladder is compressed or expanded. This is pro- 

 bably effected by the contraction or dilatation of 

 the ribs, at least we often see fishes rise or descend 

 in the water without a visible effort of any kind. 

 At all events, it is certain that when the air-blad- 

 der bursts, the fish remains at the bottom, usually 

 turning up its belly, or exhibiting other irregulari- 

 ties in its attempts at locomotion. Another curious 

 effect is observable in regard to fishes which have 

 been suddenly brought from a great depth by means 

 of a long fishing line, and which having no time 

 either to compress or partially empty the organ in 

 question, the air which it contains being no longer 

 pressed by the heavy weight of water, either ex- 

 pands so as to burst the bladder, or by its dilata- 

 tion forces the stomach and oesophagus into the 

 fish's mouth. When it is pierced artificially, the 

 fish almost immediately turns upon its back, and 

 sinks to the bottom. Though of the highest im- 



