FISHES 1353 



abled not only to live, like the climbing perch, out 

 of water, but that they die if kept below the surface 

 of the water even for a comparatively short time. 

 Thus when an Ophiocephalus and a carp were placed 

 together in a vessel of water, a net being placed 

 about two inches from the surface, the carp swam, 

 as might be expected, freely and continuously below 

 the surface, while the Ophiocephalus made vigorous 

 efforts to attain the surface, for the purpose of in- 

 haling air directly from the atmosphere. When not 

 allowed to reach the surface, the Ophiocephali died, 

 suffocated, in periods varying from twenty minutes 

 to two hours. The explanation of the power pos- 

 sessed by the latter fish", of being able to live out of 

 water, resides in the fact that these fishes possess two 

 cavities in the throat, in which blood is purified by 

 the inhalation of atmospheric air. Thus the Ophi- 

 ocephalus not only can exist out of water, but escape 

 from that medium must, in fact, be viewed as an ab- 

 solute necessity for the normal life of the animal. 

 The climbing perch appears also to exhibit this 

 latter peculiarity of requiring to escape periodically 

 from the water, for this fish, like the Ophiocephalus, 

 may be actually drowned, if kept from obtaining a 

 supply of atmospheric air. 



The curious Lepidosirens or mud-fishes, which 

 occur in the Gambia of Africa and the Amazon of 

 South America, exhibit a greater peculiarity of 

 structure, which still more completely fits them for 

 living out of water. In the great majority of fishes, 

 a curious sac or bag known as the swimming or air 

 bladder is found. The use of this structure in or- 



