170 ANNALS NEW YORK ACADEMY OF SCIENCES 



1. The chief cause of the drumming is the contraction of the drumming 

 muscles. 



2. As the myogram distinctly shows, the contraction of the drumming 

 muscles is of the nature of a series of simple contractions. 



3. These muscles contract at a definite rate, viz.: 24 vibrations per 

 second. 



4. By the force of each contraction the abdominal organs are set into 

 vibration, especially the walls of the air-bladder. 



5. The elastic walls of the air-bladder are always tense, because of the 

 pressure of the contained gas. This pressure is increased each time the 

 drumming muscles contract. 



6. The vibration of the tense walls of the air-bladder and the contained 

 gas are sufficient to produce the drumming noise. 



7. The sound produced is low. The actual number of sound vibrations 

 was not determined. 



Sound production in the Sea-Eobin and the Toadfish. 



Experiments to Determine Cause of Sound and Character of 



Mechanism. 



If a sea-robin is examined under artificial respiration, the single twitch 

 of the abdomen when a grimt is made can be very easily observed. If 

 the animal is opened along the mid-ventral line, both the contraction of 

 the intrinsic muscles and the single twitch of the swim-bladder can be 

 observed. The noise is of the same pitch and loudness after the abdomen 

 has been opened as before. The removal of all the viscera except the air- 

 bladder has no effect on the noise produced. It is noticed that the two 

 muscles contract simultaneously. 



Experiment XX. — aVn animal under artificial respiration was opened, and 

 various parts of the bladder were stimulated by a current from an induction coil, viz. : 



a. One of the two nerves suppljnng the bladder was stimulated. A perfectly 

 normal grunt was produced. 



b. The fibrous part of the bladder was then stimulated. A normal grimt was 

 not produced. 



c. The muscle itself was stimulated directly. Again a perfectly normal sound 

 was produced. 



These experiments show only that artificial stimulation of either nerve 

 or muscle will cause a normal sound to be produced. 



