FISHES. 373 



greater quantity, and he once found it to amount to eighty-seven cen- 

 times*. 



The most ohvious use of the natatory bladder is to keep the fish in 

 equilibrium with the water, or to render it heavier or lighter than 

 that fluid, and to allow it to descend or rise, according as it com- 

 presses or dilates this organ. To accomplish this, it is only necessary 

 for the fish to approximate to, or separate the sides from, each other. 

 It is certain that fishes, in which it has keen burst, remain at the 

 bottom of the water, and are turned upside down, no longer enjoying 

 the facility of motion which they exercised before. 



A curious phenomenon occurs when fishes are caught by the line, 

 and which are fished up from a great depth with such expedition, 

 that they have not time to compress their bladder, or to empty it of 

 the air it contains ; this air, being no longer compressed by the large 

 column of water which pressed upon it, bursts the bladder and diffuses 

 itself in the abdomen; it dilates it to a great extent, and pushes the 

 oesophagus and stomach into the mouth. f 



It has been thought j; that, the natatory bladder may be also an aux- 

 iliary to the organs of respiration ; it is certain that when a fish is 

 deprived of it, the production of carbonic acid by its gills is almost 

 reduced to nothing §. 



But, as to what has been said respecting its being essentially the 

 analogue of the lungs, because in certain species it communicates 

 with the oesophagus, and because it is not more destitute of cells and 

 vessels than the lungs of salamanders, for example, we must declare 

 that this does not appear to us to rest upon any real foundation. 



Not only is there no resemblance in the distribution of vessels ; 

 not only has the natatory bladder of an infinite number of fishes — of 

 indeed by far the greatest number without any comparison — no direct 

 external communication ; but in many it isat the bottom of the stomach, 

 that the canal by which it is made, opens, and, in fine, in the species 

 even in which this communication takes place by the oesophagus, it is 

 not in the same relative connexion ; but is above that the natatory 

 bladder opens into the canal, whilst the lung always communicates 

 with it below (a). 



* See on the air contained in the 'swimming bladder, the Memoire of M. Bict, 

 in the first volume of la Socidte d'Arcueil, p. 252, 1S07 ; part of this of M. M. Pro- 

 vencal and of Humboldt, on the respiration of fishes, same work, vol. II, p. 359, 

 1809 ; and the work entitled : Sull' analisidell' aria eontenuta nella vescica natatoria 

 dei pesci ; memoria di Pietro Configliacchi ; Pavie : 1 S09, in 4to. 



f This was observed in the Mediterranean by M. M. Bict and De Larochc. 



X M. Gotthelf de Fischer, on the natatory bladder of fishes. Leipsic, 1 795. 



§ This is the result of the experiment by M. M. de Humboldt and Provencal, 

 lac. cit. 



fj^* (a) Upon tbi~ singular organ much light has been thrown in modern times ; 

 the principal facts connected with it have been recently collected by Dr. 'liedmann, 

 professor of Anatomy and Physiology at the University of Heidelberg, and t"> him we 

 are indebted for the following summary . 



The impression of most naturalists is that the greater part of the fishes possess, 

 independently of their gills, another organ analogous to the lungs, which is the 

 natatory or swimming bladder. This organ is situated in the abdominal cavity, 

 along the inferior surface of the vertebral column, and it generally communicates with 



