132 The Life Story of the Fish 



trained to sounds, but they had to be a great deal louder. 

 He found that the characins showed a well-developed sense 

 of hearing; and that the mormyrids, Egyptian fish from the 

 Nile in which the air-bladder makes a direct connection with 

 membranes in the cranium, hear as well as the minnow. 

 Other species which lack the ear-air-bladder connection heard 

 much less acutely j they could be trained to sounds, but the 

 sounds had to be much louder. From this the trout and black 

 bass anglers may take comfort, for absence of the connection 

 in these fishes may be taken to indicate poor perception of 

 sounds made in the air. 



So the controversy 'has been settled, and it is accepted that 

 in many fishes the Weberian ossicles are a part of the hearing 

 apparatus which serve to transmit vibrations to the ear from 

 the air-bladder, which acts as a resonant sounding-board. 

 And to complete the argument, it is now known that, at 

 least in many of these fishes, the forward compartment of 

 the air-bladder can be closed off by a sphincter muscle, so 

 that it can be kept taut no matter what the condition of the 

 rest of this organ. 



Thus, while there are still things about the air-bladder 

 that we do not understand, there are many things which we 

 actually do know. In the first place we definitely know that 

 it still retains to some extent its original respiratory func- 

 tion. This, its primordial duty, is still one of its most wide- 

 spread and most important ones. In the lung-fishes, those 

 five species of living fossils scattered through Africa, South 

 America, and Australia, this is true to such an extent that 

 ProtofteruSy the African form called by the natives Kamongo, 

 can no longer breathe water through his gills. If caught in a 

 net so that he cannot reach the surface, he soon drowns; and 

 he can live literally for years in the cocoon of dried mud 

 which he makes for himself when the waters of his swamp 

 disappear, in Devonian style, during times of drought. 



