353 



in the air; but they absorb the gazeous oxygen, 

 like a reptile furnished with lungs. It is known, 

 that carp may be fattened by being fed out of 

 the water, and wetting their gills from time to 

 time with humid moss, to prevent their drying. 

 Fish separate their gill-covers wider in oxygen 

 gas, than in water. Their temperature, how- 

 ever, does not rise ; and they live the same length 

 of time in pure vital air, and in a mixture of 

 ninety parts azot and ten oxygen. We found, 

 that tench (cyprinus tinea), placed under in- 

 verted jars filled with air, absorb half a cubic 

 centimetre of oxygen in an hour. This action 

 takes place in the gills only ; for fishes, on 

 which a collar of cork has been fastened, and 

 leaving their head out of the jar filled with air, 

 do not act upon the oxygen # by the rest of 

 their body. 



The swimming-bladder of the gymnotus, the 

 existence of which Mr. Block has denied, is two 

 feet five inches long in a fish of three feet ten 

 inches -f\ It is separated by a mass of fat from 



* M4m. de la Soci4tt d'Areueil, vol. ii, p. 398. Ts the respi- 

 ration in the air effected through the intermedium of a plate 

 of water, infinitely thin, which moistens the gills ? 



t Mr. Cuvier has shown me, since my return to Europe, 

 that in the gymnotus electricus there exists, besides the large 

 swimming bladder, another bladder, situate before it, and 

 much smaller. It looks like the bifurcated swimming bladder 

 in the gymnotus aequilabiatus, of which I made a drawing. 



VOL. IV. 2 A 



