1911] Pemberton — The Sound-Making of Dipiera and Hymenoptera 117 



Experiment III. 



To prove that the spiracles have nothing to do with this note 

 and that they are not needed in connection with the wing muscles 

 in the sound production, the abdomen was cut off, likewise the 

 head, and the thoracic spiracles securely cemented with collodion. 

 Under these conditions the free wing-stubs still vibrated a little 

 and produced the familiar buzz for a short time. By leaving the 

 head intact in this experiment the note was as strong and clear as 

 in a fresh uninjured specimen. A fresh fly with all spiracles 

 securely closed and wings cut off, can be made to produce the 

 loud hum and stop at will by holding or releasing the wing-stubs 

 with a needle. 



In another case the thoracic spiracles were completely destroyed 

 with a needle, and the abdomen cut off, but the wings left free. 

 The usual high-pitched buzz or hum was still produced. 



Now, combining the fact that no sound, in any single case, was 

 produced with spiracles open and wings secured from action, with 

 the fact that sound, high and clear, was produced in every case 

 with wings cut off or intact, but free at the base, even though all 

 the spiracles were securely closed, we have, it seems to me, positive 

 proof as to the cause of all the audible sounds produced by this fly. 



A further experiment was made which verifies in a way what has 

 already been proved. 



The wings were pulled from an adult in such a manner as to 

 remove them completely, leaving no traces of the bases. No 

 sounds were produced. Landois believed to have done this, but 

 seems only to have cut the wings off as closely as possible. It 

 would be impossible to cut off the wings without leaving some very 

 small portion which would be large enough to vibrate and produce 

 a sound. 



The above experiments were carefully repeated several times 

 with the same results in every case. They seem to prove quite 

 conclusively that the supposed sound of the spiracles is merely a 

 buzzing of the wing-bases or a striking of them against a portion 

 of the body-wall adjoining them. The well-adapted character of 

 the spiracles for the production of sound if air could be very 

 violently forced through them, combined with the confusing fact 

 that the same pitch of sound is produced both with the wings cut 



