72 BRAIN AND BODY OF FISH 



fibres and the bladder has thick strong external muscles supplied 

 by two large nerves from the anterior part of the spinal cord. 



According to Moreau, the diaphragm is thrown into vibrations by 

 air being forced from one compartment to the other. In these 

 fishes, it has been shown that the somid is produced by intrinsic 

 muscles in the wall of the air-bladder, and a grunt is caused by a 

 single contraction of these muscles : it can be called forth by electric 

 stimulation even in a bladder which has been removed from the 

 fish. The sound was not produced when the bladder was empty, 

 but returned when a rubber bladder was put inside the natural one ; 

 this proves that a diaphragm is not essential for the production of 

 the grunt. The grey gurnard is a fish of considerable interest apart 

 from its grunting, there is the strange develoj^ment of its pectoral 

 fin rays into fingers, and the pearl-like enlargements of its spinal 

 cord, associated with this special adaptation. The maigre shows 

 by its large otoliths the connection of voice wdth hearing. It is 

 found, when the brain of the grey gurnard is examined, that it has 

 a highly developed central acoustic lobe very similar to that found 

 in the j)ilchard. This can apparently be associated with hearing, 

 as most fish with closed swim-bladders and a bottom -feeding habitat 

 do not show a central acoustic lobe, but only a rudimentary acoustic 

 area. 



It will have been noticed, that in the two families, the Sciaenidse 

 and Triglidse, the production of sound is dependent on the air- 

 bladder, and that the vibrations originate in connection with a 

 gaseous medium, and are produced by the organ which is homologous 

 with the lung, by which the voice of terresterial vertebrates is 

 produced. There are other methods of sound production in aquatic 

 animals, as example, the stridulating organs of members of the 

 Siluroid family, as seen in certain Indian species. The WTiter of 

 the above-mentioned article, to whom we are indebted for many 

 of our facts, describes the production of sound by a trigger-fish 

 " Balistes," which is abundant round the Island of Ascension. He 

 observed " behind the pectoral fin an area of skin, resembling a 

 drum, a portion of the air-bladder lying just beneath it. When the 

 drumming sound was produced the pectoral fin was moved rapidly 

 to and fro and the membrane could be seen to vibrate. No sound 

 was produced when the fin was held stationary." 



Hitherto, w^e have mentioned mostly dwellers in the sea that pro- 

 duce sounds, but we must not forget to mention that the air-bladder 

 functions as a sound producing organ in many fresh-water fishes. 

 The blind fish of tlie Mammoth Cave of Kentucky calls to its felloA\'s 

 by sounds, and the blind fish (Lucifuga) that lives in the subterranean 



