PRODUCTION OF SOUND 409 



dead fish, but the sound is probably accidental and of no import- 

 ance. In the drumming trigger-fish (Balistes aculeatus) which 

 lives among the coral reefs of Mauritius, there is an apparatus 

 whose sound-producing function seems beyond doubt. It 

 consists, according to the German naturalist Mobius, in the 

 movement of certain bones of the pectoral girdle against one 

 another. Both these bones are in close contact with the air- 

 bladder, and the walls of the latter are over a certain area in 

 contact with the skin which is seen to vibrate when the sounds 

 are being emitted. Here again, therefore, we have the air- 

 bladder and its gaseous contents playing an important part in 

 the production of sound. 



The present writer recently had an opportunity of studying 

 the production of sound in a species of trigger-fish, Batistes 

 buniva, which is very abundant at the island of Ascension in 

 the Atlantic. When the mail steamer on which the writer was 

 a passenger anchored off the island, shoals of this fish gathered 

 round the ship to feed on refuse thrown overboard, and from a 

 boat at the foot of the ladder he was able to take a specimen 

 alive with his hand. Just behind the pectoral fin is an area of 

 the skin resembling a drum, a portion of the air-bladder being 

 immediately beneath it : this drum is distinguished from the 

 surrounding skin by being covered with large scales meeting 

 edge to edge, not overlapping like the ordinary scales. When 

 the drumming sound was produced the pectoral fin was moved 

 rapidly to and fro and the membrane of the drum could be seen 

 to vibrate. When the pectoral was forcibly kept motionless in 

 a forward position by the finger and thumb, no sound was pro- 

 duced. It certainly seemed as though the sound was due to the 

 vibrations of the drum itself, and as though these vibrations were 

 due to the striking of the drum by the fin, but it was impossible 

 to decide whether the friction of the internal bones of the 

 pectoral girdle was necessary to produce the sound as Mobius 

 states. There can be no doubt that the vibrations of the drum 

 give rise to the sound, the only question is whether these vibra- 

 tions are caused by the pectoral fin striking the drum externally, 

 or by the friction of the bones internally. 



Lastly, it maybe mentioned that some fishes make sounds 

 by grating together their upper and lower pharyngeal teeth. 

 This has been proved to occur in the common scad or horse- 



