382 ZOOLOGY. 



of the gills on either side : in those with fixed gills, there are 

 as many apertures as branchiae. Thus, in the shark (Fig. 392) 

 there are five pairs of openings, and in the lamprey (Fig. 409) 

 seven. Hence the nature of the respiratory apparatus may be 

 known by an inspection of the exterior. Finally, in some fishes 

 (the lamprey), the water entering by the mouth reaches the 

 gills through a kind of canal placed under the gullet, and 

 interposed between the cavity of the mouth and that for the 

 gills; the arrangement resembles in some measure the trachea 

 of the higher organized animals. 



Fishes do not consume much oxygen ; nevertheless, some 

 come to the surface from time to time to breathe air, as if 

 that absorbed by the gills was not sufficient. Some even 

 swallow it, and convert the oxygen into carbonic acid whilst 

 passing through the intestines ; the loach of still waters 

 presents this singular phenomenon. When removed from 



Fig. 392.-The Shark. 



water into the air, most fishes speedily become asphyxiated, 

 not from the absence of oxygen, but because the branchial 

 laminae, no longer floating in water, collapse, and exclude the 

 access of air ; they also dry up, and become unfit for the 

 exercise of their functions. The larger the external aperture 

 of the gills, the speedier does death ensued 



The family with labyrinthiform pharyngeals* have recep- 

 tacles in which they can preserve water, as in reservoirs, to 

 moisten the branchiae : these receptacles are ^ater-collecting 

 cells placed above the branchiae ; hence the name of the 

 family. 



These cells (Fig. 393), enclosed under the gill-cover, and 

 formed by the lamellae of the pharyngeal bones, retain a cer- 



* Examples : andbas scandens, climbing fish ; osphromenus olfax, the 

 gourami. E. K. 



