296 FISHES CHAP. X 



marshes, lurking in holes in the grass and about the sides of 

 ponds. In fact, even when in the water, access to air, which is 

 probably swallowed and passed over their accessory breathing 

 organs, is indispensable to their existence. Experiments con- 

 clusively prove that if the Fish is artificially prevented from 

 obtaining air in this way asphyxiation speedily ensues.^ 



In addition to breathing air through the agency of special 

 organs evolved for the purpose, there are many freshwater Fishes 

 which, like those just mentioned, periodically rise to the surface 

 and swallow air in order to saturate the water which bathes the 

 gills with oxygen.^ 



^ For much interesting information on aerial respiration in Fishes, see Day, 0^. 

 cit. ; also P.Z.S. 1868, p. 274 ; and Dobson, ibid. 1874, p. 312. 



^ Semper, Animal Life, Intern. Sci. Series, London, 1881, p. 172. 



