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.’ 
1 For much interesting information on aerial respiration in Fishes, see Day, op. 
cit.; also P.Z.S. 1868, p. 274 ; and Dobson, ibid. 1874, p. 312. 
2 Semper, Animal Life, Intern. Sci. Series, London, 1881, p. 172. 
