218 THE VITAL FUNCTIONS. 



In all osseous fishes the opening under the operculum for 

 the exit of the respired water, is a simple fissure; but in 

 most of the cartilaginous tribes, there is no operculum, and 

 the water escapes through a series of apertures in the side of 

 the throat. Sharks have five oblong orifices of this descrip- 

 tion, as may be seen in f^ig. 367.* 



As the Lamprey employs its mouth more constantly than 

 other fish in laying hold of its prey, and adhering to other 

 bodies, the organs of .respiration are so constructed as to be 

 independent of the mouth in receiving the water. There 

 are seven external openings on each side (Fig. 368,) lead- 

 ing into the same number of separate oval pouches, situated 

 horizontally, and the inner membrane of which has the same 

 structure as gills: these pouches are seen on a larger scale 

 than in the preceding figure, in Fig. 369. There is also an 

 equal number of in tern -xl openings, se?n in the lower part 

 of this last figure, leading into a tube, the lower end of which 

 is closed and the upper terminates by a fringed edge in the 

 oesophagus. The water which is received by the seven la- 

 teral openings, enters at one side, and after it has acted upon 

 the gills, passes round the projecting membranes. The 

 greater part makes its exit by the same orifices; but a por- 

 tion escapes into the middle tube, and thence passes, either 

 into the other cavities, or into the cesophagus.t 



life, when surrounded by air instead of water, is that the branchiae become 

 dry, and lose the power of acting when thus deprived of their natural mois- 

 ture: for it might otherwise naturally be expected that the oxygen of atmo- 

 spheric air would exert a more powerful action on the blood which circulates 

 in the branchiae, than that of merely aerated water. The rectification of this 

 error is due to Flourens, who pointed out the true cause of suffocation, stated 

 in the text, in a Memoir entitled ** Experiences sur le Mechanisme de la Res- 

 piration des Poissons." Annales des Sciences Naturelles, xx. 5. 



* They are also visible in Fig. 293, (page 122,) which is that of the^wa- 

 luspristis, a species belonging to this tribe. 



j- It was commonly supposed that the respired water is ejected through 

 the nostril; but this 5s certainly a mistake, for the nostril has no communi- 

 cation through the mouth, as was pointed out by Sir E. Home. Phil. Trans. 

 for 1815, p. 259. These organs have also been described by Bloch and 

 Gartner. 



