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Show 1868.] DR. F. DAY ON INDIAN FRESHWATER FISHES. 281 for the same reason termed olfax. Cuvier observes of his Labyrinthici that the superbranchial cavities are qualified to contain a certain amount of water, somewhat like the spongy stomach of a camel*. Owen says that "Accessory respiratory organs, acting chiefly as a reservoir or filter of water, are developed from the upper part of the pharynx in the climbing perch ( Anabas scandens) and allied fishes of amphibious habits"-]-. Giinther, with reference to this, states that the Labyrinthici " appear to contain, or to collect, a small quantity of water in the cavity in which the superbranchial organ is situated" J, and that the " Ophiocephalidae have a cavity accessory to the gill-cavity for the purpose of retaining water in it "§. Following these and other authorities, it had appeared to me that this cavity was for the retention of water, to enable the fish to travel on dry ground by moistening the gills, and thus obtaining oxygen from the atmosphere. But having now had opportunities of personally investigating the question, I have drawn the following conclusions:- 1st, that these fishes died, when deprived of access to atmospheric air, not from any deleterious properties either in the water or in the apparatus used, but from being unable to subsist on air obtained solely from the water, aerial respiration being indispensable ; 2nd, that they can live in moisture out of water for lengthened periods, and for a short and variable time in water only; lastly, that the cavity or receptacle does not contain water, but has a moist secreting surface, in which air is retained for the purposes of respiration; and it seems probable that this air, after having been employed for this purpose, is ejected by the mouth, and not swallowed to be discharged per anum. Some of the venous blood appears to be oxygenated at the gills, and the remainder in the cavity above the gills by means of air; but if the fish be kept under water without air, this cavity, which is surrounded by bony tissue, becomes filled with water, which cannot be discharged, owing to its almost non-contractile powers. There is thus no means of emptying it, and the water probably becomes carbonized and unfit for oxygenizing the blood, so that the whole of the respiration is thus thrown on the branchiae. This will account for the fact that, when the fish is in a state of quiescence, it lives much longer than when excited, whilst the sluggishness sometimes evinced may be due to poisoned or carbonized blood. A good example of an air-breathing fish is afforded by the singular-looking finless snake-like eel, the Symbranchus cuchia, Ham. Buch., in which respiration is carried on in a receptacle above the branchial arches on each side of the head-a discovery which was made many years ago by Dr. Taylor at Dacca. It is found in the Indian marshes, lurking in holes; and the following remarks are made by Professor Owen on its respiratory apparatus || : - " The second branchial arch supports a few long fibrils, and the third a simple lamina, fringed * Cuv. & Val. vol. viii. p. 323. t Lectures on Comparative Anatomy, 1866, vol. i. p. 487. % Catalogue of Fishes, vol. iii. p. 372. § Ibid. p. 468. || Anatomy of Vertebrates, 1866, vol. i. p. 487. |