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FACULTIES OF BIRDS. 



In fishes (for the whale, being a warm-blooded 

 animal and breathing the air, is not considered a fish), 

 the buoyancy indispensable for swimming is effected 

 by a very different contrivance. A bladder, varying 

 in form in different species, is filled with air (azote in 

 fresh water, and carbonic acid gas in marine, fishes), 

 over which the animal appears to possess a voluntary 

 power, either to empty it by compression or fill it by 

 distension. Now it is obvious that, by the effort to 

 compress the swimming-bladder, the body of the fish 

 must be contracted,, and consequently, as the absolute 



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

 ming-hladder. B, In the Conger Eel: a, the stomach; 6 b, the 

 swimming-bladder. 



