156 



A HISTORY OF FISHES 



in a certain plane this apparatus is brought into play and harsh, 

 grating noises are produced. 



In the remaining sound-producing fishes to be discussed, the 

 organs are for the most part of a more elaborate nature, and the 

 noise is produced through the agency of special muscles associ- 

 ated with the air-bladder. In a number of Cat-fishes {Siluroidea) 

 an apparatus known as the elastic spring mechanism occurs, 

 the purpose of which is to cause the walls of the air-bladder to 

 vibrate. The "springs" are specially modified portions of the 



Oesqx?/ia^u.s 



n'-rii 



Fig. 64. — SOUND-PRODUCING ORGANS. 



B 



A. Elastic spring mechanism of a South American Cat-fish (Auchejjiptcrus 

 nodosus), showing the oval bony plates in which the elastic springs terminate, 

 X about |. (After Bridge and Haddon) ; b. Air-bladder of a Sciaenid {Micro- 

 pogon undulatus), showing the musculo-tendinous extensions from the muscles 

 of the body- wall, which partially invest the surface of the bladder (?«.), X about ^. 



(After Sorensen.) 



fourth vertebrae and their expanded ends are attached to the 

 front part of the air-bladder (Fig. 64A). Two strong muscles 

 run from the springs to the hinder portion of the skull, and 

 when these contract the springs, and with them the walls of the 

 bladder, vibrate rapidly and produce a sort of growling or 

 humming noise. Generally, the air-bladder is divided up by 

 internal partitions into a number of chambers all freely com- 

 municating with one another, and there can be no doubt that 

 the sound is intensified by the vibratory movements of the gases 

 contained in the bladder across the free edges of the partitions. 

 In the Sciaenids or Drums {Sciaenidae), fishes renowned for their 



