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1Some relation witli the respiratory functions, and as being the rudiment of the 

 piilmonary tavity of land animals, the passage of communication with the 

 CBSophagus being conceived to represent the trachea." Harvey observed that 

 the air in birds jiassed into cells beyond the substance of the lungs, thus showing 

 a resemblance to the cellular lungs of reptiles, and the air bladder in fishes. 

 M. Agassiz, in dissecting a species of Lepidosteus, or "bony Pike," a fresh water 

 fish of North America, found the ah' bladder to be composed of several cells, with 

 a tube proceeding upwards into the pharynx, and entering by an elongated slit, 

 having everted edges, resembling a glottis or tracheal aperture. Yarrell states 

 that various Siluroids and Pi'otopteri possess air bladders with similar pulmoni- 

 form complications, and that though it is generally admitted that the chief 

 function of the air bladder is to regulate the specific gravity of the fish, yet 

 comparative anatomists consider it to be the homologue of the lungs of the 

 air-breatliing vertebrata, or the rudimentaiy state, in which that organ first 

 appears in the ascending scale of the animal creation. 



Carpenter says that " the cavity of the air bladder is in some instances so 

 divided by membranous partitions, as to give to the organ the character of the 

 lung of a reptile. The time relations of this organ are most remarkably shown 

 in the Lepidosteus, which presents many reptilian affinities. Another fish may 

 also be mentioned as presenting an apparatus adapted for atmospheric respi- 

 ration, which is rather a peculiar development of the bronchial apparatus than 

 the rudiment of a lung of air-breathing vertebrata. This is the Cuchia, an 

 eel-like fish of the Ganges, in which saccular prolongations are found in one of 

 the gill-chambers used for atmosjiheric respiration. The power which this 

 animal has of distending the respiratory sacs with air when on land, and the 

 necessity it is nnder of rising to the surface of the water for the same puriJose 

 prove beyond a doubt that they perfonn the function of lungs, and lead us to 

 the conclusion that tlie Cuchia is amphibious in the strict sense of the word — 

 forming a connecting hnk between the Ojihidian reptiles and the Synbranchus 

 among fishes. In some other fish, especially such as naturally inhabit small 

 collections of fresh water, whose temperature is liable to be considerably raised 

 during the heat of summer, the mucous lining of the alimentary canal appears 

 to act as an additional organ of respiration ; for such fish are seen frequently to 

 rise to the surface, and swallow air, which is subsequently discharged by the 

 anus with a large quantity of carbonic acid substituted for its oxygen. This is 

 the case with the Cohitis (Loach) ; and it would seem as if under these circum- 

 stances some such supplemental means is required for carrying on the respiratory 

 process vidth unusual activity." Carpenter sums up thus : That where there is a 

 short and wide opening to the oesophagus the air-bladder may serve as an 

 accessory organ of respiration, atmospheric air being taken in, and carbonic acid 

 ejected thi-ough the alimentary canal ; but in those whose air-bladder is a closed 

 sac, it seems that it cannot in any way conduce to the aeration of the blood. 

 This appears to be one of the many instances which may be ijointed out in the 

 animal aad vegetable kingdoms, where the rudimentary form of an organ that 



