THE AIR OR SWIM-BLADDER OF FISHES. 

 BY JOHN LLOYD, Esq. 



Whether we examine, as is the wont of the members of our 'Woolhope 

 Club, the position and nature of the primeval rocks, the parts and functions 

 of animals, the stmcture and uses of plants, or other special branches of natural " 

 history, in all aUke we find signs of the wise providence of oui" Creator. In 

 earth, air, and water, and in their denizens, animate and inanimate, we see the 

 wonders of the creation displayed, and a marvellous adaptation throughout, of 

 the means to the end. 



The birds when formed to fly in the air had wings given them, and their 

 locomotive powers specially adapted to act upon that medium ; and fish likewise 

 were furnished with fins framed to act with the greatest power on their element, 

 water— and in both auxiliary air cavities are provided. 



In birds the central cavity of the bones, usually occupied by maiTow, is 

 fiUed with air ; and it has been found that in proportioH as their bones are 

 connected with the respiratory process, and their interior filled with air instead 

 of marrow, so are their special powers of flight increased. In fish the air cavity 

 is the subject of this paper— the Air or swim-bladder. Here it has been said that 

 those capable of the most vehement and prolonged efforts possess the largest air 

 bladders, and those with the quickest action. In the cases both of the bird and 

 the fish the chief and primary object is by the introduction of a considerable 

 quantity of aii- to lessen the specific gi-avity, and thus aid locomotion ; and in 

 proportion to the amount of air thus held, their speed and power of progression 

 is in both animals much enhanced. 



The Air bladder of a fish is a most beautiful and admirable device. Paley 

 calls it a philosophical contrivance, and brings it forward in his "Natural 

 Theology" as an instance of the wise design of the Creator. He further says : 

 " The principle of the design is clear, and the application of the principle is 

 clear also." The principle is clear enough, it is true, but its application in all 

 cases is far from being so. The subject of the Air-bladder of fish has engaged the 

 attention of the most eminent naturalists, including Munro, Lacepede, St. 

 Hilaire, Cuvier, Miiller, Owen, and MUne Edwards, and though all agree as to 

 the principle, yet they differ widely as to the application. In preparing this 

 paper, and following them through the mazy labyiinths of their disquisitions, 

 the endeavour is made to get hold of some clue, which, if not entirely explaining 

 this vexato quwstio, may help us on our path. 



