TOWER, PRODUCTION OF SOUND IN CERTAIN FISHES lt)7 



Experiments to determine character of the muscular contraction. 



The character of the contraction of the red drumming muscles has never 

 been studied, nor has the relation of the contractions to the pitch of the 

 drumming been accurately recorded. Dufosse has given the pitch of the 

 drumming of the meagre as well as he could determine it by the ear alone. 

 The following experiments were performed in canying on the present study: 



Experiinent XI. — The first experiment was made so as to record the number 

 of vibrations produced by the abdominal tissue in the mid-ventral line during the 

 process of drumming. To accomplish this, a light wooden lever was made, with a 

 piece of sheet cork two inches long and one half inch wide attached at the bottom, 

 and a fme wire inserted in the top at right angles to the lever. The cork was held in 

 place on the abdomen of the squeteague by two rubber bands going around the fish 

 and over each end of the cork strip. The revohnng drum of the kymograph was 

 then placed so that the wire point would trace on the smoked paper of the drum. 

 Thus when the animal commenced to drum, the vibration of the part of the abdomen 

 under the lever would be traced by the writing point on the smoked paper. The 

 drum of the kymograph revolved once in 4.848 seconds, and its circimaference was 

 48.5 cm. The tracings are given on PL VIII, fig. 1. The number of vibrations 

 per second, as determined by comparison with the tracings of a tuning fork vibrated 

 100 times per second, is 24. 



Exferiment XII. — A control experiment was made the next day on another 

 squeteague, but with the drum of the kjTnograph revohing only once in 20.202 

 seconds. The number of vibrations should agree or at least be within the limits of 

 experimental error. The tracings are given on PI. VIII, fig. 2. The number of 

 vibrations is again 24 per second. 



In both of the above experiments the lever Wiis placed on the mid-ventral 

 line just posterior to the pectoral fuis. 



Experiment XIII. — The next experiment was to determine whether the anterior 

 and posterior ends of the abdomen vibrated synchronously, or whether the \abration 

 passed over the abdomen like a wave, from anterior to posterior, or \dce-versa. 

 Mere observation as well as the resting of the fingers on the anterior and posterior 

 parts at the same time detected that all the muscle-fibres contracted synchronously. 

 To determine this more accurately, two levers were arranged — one being placed 

 just posterior to the pectoral fins, and the other just anterior to the anus — so that 

 they should write under each other on the smoked paper. The traces indicated 

 that the entire abdominal mechanism vibrated synchronously; hence all the fibres 

 of the two drumming muscles contract at the same time under stimuli controlled by 

 the central nervous system of the animal. 



Experiment XIV. — In a fresh male squeteague an incision one inch long was 

 made on one side through the thick, white abdominal muscles imtil the red m. 

 sonificus was exposed. The cork base of the lever was inserted through this opening 

 until it rested on the red muscle within. With the lever in this position and the 



