TOWER, PRODUCTION OF SOUND IN CERTAIN FISHES 165 



drumming noise ; and the forcing of air into the lateral horns, if such takes 

 place, is not the true explanation. 



It remains now to consider the views of Dufosse and of Sorensen. Is 

 this drumming a muscular tone, i. e., a sound produced by the vibrating 

 muscle and intensified by the air-bladder (Dufosse), or do certain muscles 

 set into vibration the air in the air-bladder and the walls of the latter 

 (Sorensen) ? 



Experiment VII. — The entire abdominal viscera except the air-bladder were 

 removed. Contractions of the muscles occurred, but no noise. The rubber balloon 

 was inserted into the abdominal cavity and inflated (the air-bladder being intact 

 and inflated). The drumming returned. When the balloon was allowed to collapse, 

 the noise ceased. 



c. The abdominal ca\'ity was packed tight with cloth (the air-bladder being 

 intact and full of air). The drumming was loud, and when the cut edges were drawn 

 together, it increased to a nonnal di-um. When the cloth packing was removed, 

 the muscle still contracted, but no noise was heard. When the ca\'ity was packed a 

 second time with cloth, the drumming became again audible. 



Experiment VIII. — The entire viscera, including the air-bladder, were next re- 

 moved. Notwithstanding the large hemorrhage that occurred, the sonifici still 

 contracted. The rubber balloon was inserted and inflated wath air. The drumming 

 noise returned of apparently the same pitch but not so loud as normal. 



a. The central tendon was then cut longitudinally into two parts. The muscles 

 on either side contracted rhythmically, as could be seen from the vibrations of the 

 cut ends of the tendon. There were, however, no vibrations of the abdominal 

 muscles, such as are seen in normal animals. This was as might be expected, because 

 after cutting the central tendon the two drtimming muscles have nothing to work 

 against. The inflated rubber balloon now produced no sound. This seems to show 

 that the air-bladder does not act as an intensifier of muscular tone. The experiment 

 suggests that the air-bladder functions either in maintaining the tension inside of the 

 abdominal cavity, or as a vibrating organ or both. 



Experiment IX. — Incisions were made on both sides of the median line of the 

 abdomen. After this operation the drmnming remained perfectly normal. The 

 m. sonifici were then cut from their origin on the abdominal muscles. One side was 

 amputated first, and the drvraiming still continued. While the one on the opposite 

 side was being cut, the drumming died away gradually until the drumming muscle 

 was severed its entire length, when the noise ceased. Yet at this time the muscle 

 contracted, as could be easily felt by touching it with the finger. 



If now the air-bladder served as an intensifier of the muscular vibrations, 

 Ave might ask why it suddenly ceases to fulfill that function in the above 

 experiment. Also, in experiment II c, drumming occurs when the air- 

 bladder is replaced by a rubber balloon filled with water. This water- 

 bladder cannot be looked upon as an intensifier of sound or a resonator. 



The foregoing experiments show that any part of the muscle can produce 

 the drumming when conditions are suitable. We have also seen that by 



