AIR AND LIFE 147 



mouth. In the fishes the water carrying oxygen in solution 

 is taken into the mouth ; but when it gets into the throat, 

 instead of being swallowed into the gullet it is forced out 

 through a series of openings in the sides of the pharynx and 

 passes over the gills. The gills are fine, feathery structures 



FIG. 46. How the haddock breathes 



In the fishes the gills are arranged on arches along both sides of the pharynx. Water 

 is taken through the mouth and passes over the gills and out again, as indicated by 



the arrows 



containing many delicate blood vessels. As the water passes 

 over the gills the oxygen in solution diffuses into the blood 

 from the surrounding water (see Fig. 46). In the bony fishes 

 the gill-slits and the gills are covered over by a special plate- 

 like shield. 



In the amphibians the adults breathe the air into the 

 mouth and swallow it into the lungs, and all the higher 

 vertebrates breathe by means of lungs. 



