RESPIRATION IN FISHES. 219 



In the Myxine, which feeds upon the internal parts of its 

 prey, and buries its head and part of its body in the flesh, 

 the openings of the respiratory organs are removed suffi- 

 ciently far from the head to admit of respiration going on 

 while the animal is so employed; and there are only two 

 external openings, and six lateral pouches on each side, with 

 tubes similar to those in the lamprey. 



The Perca scandens (Daldorff,*) which is a fish inhabiting 

 the seas of India, has a very remarkable structure adapting 

 it to the maintenance of respiration, and consequently to the 

 support of life for a considerable time when out of the water: 

 and hence it is said occasionally to travel on land to some 

 distance from the coast, t The pharyngeal bones of this fish 

 have a foliated and cellular structure, which gives them a 

 capacity for retaining a sufficient quantity of water, not 

 only to keep the gills moist, but also to enable them to per- 

 form their proper office; while not a particle of water is suf- 

 fered to escape from them, by the opercula being accurately 

 closed. 



The same faculty, resulting from a similar structure, is 

 possessed by the Ophicephalus, which is also met with in 

 the lakes and rivers of India and China. Eels are enabled 

 to carry on respiration when out of water, for a certain pe- 

 riod, in consequence of the narrowness of the aperture for 

 the exit of the water from the branchial cavity, which en- 

 ables it to be closed, and the water to be retained in that 

 cavity.J 



I have already stated that, in all aquatic animals, the water 

 which is breathed is merely the vehicle by which the air it 

 contains is brought into contact \vith the organs of respiration. 

 This air is constantly vitiated by the respiration of these 

 animals, and requires to be renewed by the absorption of a 



* Mhiastestudinus.(R\och:) trials (Cuv.) 



f This peculiar faculty has been already alluded to in volume i. p. 301. 



t Dr. Hancock states that the Doras costaius, (Silurus cosiatus, Linn.) or 

 Hassar, in very dry seasons, is sometimes seen, in great numbers, making long- 

 marches over land, in search of water. Edin. Phil. Journal, xx. 396. 



