RESPIRATION IN FISHES. 307 



tenance 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 Opldcephalus^ 

 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 

 period, in consequence of the narrowness of the 

 aperture for the exit of the water from the bran- 

 chial cavity, which enables it to be closed, and 

 the water to be retained in that cavity. ^ 



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. 



