18G8.] DR. F. DAY ON INDIAN FRESHWATER FISHES. 281 



for the same reason termed olfax. Ciivier observes of his Laby- 

 rinthici that the superbranchial cavities are quahfied to contain a 

 certain amount of water, somevrhat 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 scmidens) and 

 allied fishes of amphibious habits"f . 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 "if, and that the " Ophiocephalidse have a cavity ac- 

 cessory 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 per- 

 sonally investigating the question, I have drawn the following con- 

 clusions: — 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 indis- 

 pensable ; 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 car- 

 bonized 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 



* Cut. & Val. vol. viii. p. 323. 



t Lectures on Comparative Anatomy, 1866, vol. i. p. 487. 



X Catalogue of Fishes, vol. iii. p. 372. § Ibid. p. 468. 



11 Anatomy of Vertebrates, 1866, vol. i. p. 487. 



