RESPIRATION IN FISHES. 305 



Death is, in like manner, the consequence of a 

 ligature passed round the fish, and preventing 

 the expansion of the branchiae and the motion of 

 the opercula. 



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 description, as may be seen in 

 Fig. 367*. 



As the Lamprey employs its mouth more con- 

 stantly than other fish in laying hold of its prey, 

 and adhering to other bodies, the organs of res- 

 piration are so constructed as to be independent 

 of the mouth in receiving the water. There are 

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

 leading 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 



acting -'ien thus deprived of their natural moisture ; for it might 

 otherwise naturally be expected that the oxygen of atmospheric 

 air would exert a more powerful action on the blood which cir- 

 culates in the branchiso, 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 Respiration des 

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



* They are also visible in Fig. 293, (page 166), which is that 

 of the Squalus pristis, a species belonging to this tribe. 

 VOL. II. X 



