172 ANNALS NEW YORK ACADEMY OF SCIENCES 



a. The bladder was then punctured and all of the air expelled from both lobes. 

 The muscle was again stimulated, but there was no sound, although the muscle 

 contracted as usual. The collapsed rubber balloon was inserted into one lobe of the 

 bladder, and then inflated. Upon stimulation a grunt was produced. The bladder 

 was now inflated still more, and upon stimulation a grunt of higher pitch was pro- 

 duced. When the bladder was inflated still more, the pitch became yet higher. 



b. The rubber balloon was now filled with sea-water and the muscles stimulated. 

 A grunt was produced, although the pitch was apparently changed. 



It is very evident then, that in the sea-robin and the toadfish the swim- 

 bladder with its intrinsic muscle is an organ for the production of sound. 

 By the contraction of the intrinsic muscle the tense walls of the air-bladder 

 are made to vibrate, thus producing the sound. 



These grunts can be imitated very closely by drawing the forefinger and 

 thumb towards each other over the surface of an inflated rubber balloon, 

 especially if the rubber is dry or has been resined. 



Conclusions. 



I. The scisenoid fishes that make a drumming noise have specific sound- 

 producing muscles which are only superficially attached to the swim-bladder. 

 For this drumming muscle the name musculus sonificus has been proposed 

 and adopted. 



II. The chief cause of the drumming noise is the contraction of the m. 

 sonificus, which produces a vibration of the abdominal walls and organs, 

 especially the swim-bladder. 



III. The sea-robin and the toadfish, which make a grunting noise, have 

 muscles which are intrinsically connected with the swim-bladder and are 

 known as intrinsic muscles. 



IV. The cause of the grunting noise is the contraction of the intrinsic 

 muscles which produce a vibration in the walls of the air-bladder. 



V. The mechanism in the Scisenoidae is adapted to the production of 

 rapidly repeated sounds or rolls. 



VI. The mechanism in the sea-robin and the toadfish is adapted to the 

 production of sounds repeated at more or less long intervals. 



