RESPIRATION IN FISHES. 307 



teiiance 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*. The pharyngeal bones of this fish have 

 a foliated and cellular structure, which gives 

 them a capacity for retaining a sufficient quan- 

 tity of water, not only to keep the gills moist, 

 but also to enable them to perform their proper 

 office ; while not a particle of water is suffered 

 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 respi- 

 ration when out of water, for a certain period, 

 in consequence of the narrowness of the aperture 

 for the exit of the water from the branchial 

 cavity, which enables it to be closed, and the 

 water to be retained in that cavity. f 



I have already stated that, in all aquatic ani- 

 mals, the water which is breathed is merely the 

 vehicle by w^hich the air it contains is brought 

 into contact with the organs of respiration. This 



* This peculiar faculty has been already alluded to in 

 volume i, p. 433. 



t Dr. Hancock states that the Doras costatus, {Silurus cos- 

 tatus, 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. 



