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Miiller's Archives, by Professor J. Van der Hoeven. The Lepido- 

 siren, too, the real ichthyic character of which has been so ably de- 

 monstrated by Professor Owen, in a late part of the * Linnean Trans- 

 actions,' is provided with a double sacculated air-bladder, precisely 

 similar to the lungs of some of the Reptilia, and with a glottis as well. 



That the air-bladder performs, in some fishes, some other function 

 than that of a float, by the compression or dilatation of which, as in 

 the philosophical toy termed the hydrostatic paradox, it may sink to 

 a greater depth or rise to the surface of the water, must, I think, be 

 allowed. Our countryman, Needham, in his work entitled ' Dis- 

 quisitio Anatomica,' published in 1667, is one of the first to venture 

 this opinion. He not only figures accurately the air-bladders in four 

 different kinds offish, but represents the blood-vessels in two of them; 

 and in the eel the two glandular bodies are shown, and the large ves- 

 sels going to and from them. He however makes no mention of the 

 minute arrangement of the blood-vessels, the only vessels he figures 

 being the large artery seen in the upper compartment. 



I will now, in conclusion, state briefly the chief points of interest 

 which may be deduced from my own observations, and what I have 

 been able to collect from the writings of others. The air contained 

 in the interior of the bladder has been analysed with particular care 

 by Priestly, Fourcroy, Configliachi and Biot, as well as by some of the 

 most distinguished chemists of the present age, and they all agree in 

 these points, that in those fish with closed air-bladders, a great pro- 

 portion of it consists of oxygen, as much as from 69 to 87 per cent., 

 whilst in those fishes in which there is a ductus pneumaticus, as in 

 the carp, nitrogen abounds, to as much as 87 per cent., whilst the 

 oxygen and carbonic acid were only about 7 and 5 per cent, respec- 

 tively. It has been before stated, that in all the closed air-bladders 

 the glandular body is found, and hence we have a right to infer, that 

 this difference in the component parts of the air may be dependent 

 upon this vascular apparatus ; besides, all these fish live, for the most 

 part, in deep water, and the bladder is thick and muscular, whilst those 

 with a duct live nearer the surface, and in them it is thin and weak, 

 and the probable use of the gland may be not to secrete air, but to 

 keep what is contained in the bladder quite pure, as these fish, from 

 having no duct of communication, cannot change the air should it 

 become impure ; besides, in these thick muscular bladders, we can- 

 not imagine that any interchange can take place between the air in 

 the bladder, and what is contained in the abdominal cavity by endos- 



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