The Buzzing of Diptera. By P. A. Aubin. 331 



margin of the wing, except at the shoulder, but the alulet, together 

 with the posterior margin of the wing, is vibrated through 

 the chitinous members 14 to 19. These vibrations have an 

 amplitude, at the tip of the wing, of approximately 1/16 of 

 an inch, but it will be seen later that they play no appreciable part 

 in the production of the buzz. The amplitude of the vibrations of 

 the parts about la and 22 are so small, and their rate so rapid, that 

 they might easily pass unnoticed : the first indication of them is 

 the apparent impossibility of bringing the parts into focus. 



It will also be observed that the halteres are thrown into a 

 state of rapid vibration and appear to strike the inferior surface of 

 the squama, but test 2 below disposes of them as sound producers. 

 It may be noted that the size of the haltere bears no proportion 

 either to the size of the insect or to the volume of sound produced : 

 thus in Eristalis the haltere is many times smaller than in Tipula, 

 which is silent, whilst the head of this organ is but very little 

 larger in Eristalis than in Musca domestica. 



Test 1. — The fly may be held in the fingers in any way but 

 one, without appreciably affecting the buzzing ; if, however, it be 

 held with finger and thumb on opposite sides of the thorax so as 

 to press the shoulders of the wings to the body, the sound at once 

 ceases. 



Test 2. — Each or all of the following parts may be removed 

 without noticeably affecting the sound : — the halteres, the squama 

 and ante-squama, the alulet, and nine-tenths of the wing. If, how- 

 ever, the wing be carefully dissected off, so as to ensure its removal 

 up to the point 7, the sound ceases. Landois' observation that the 

 thorax of a blow-fly continued to buzz after the removal of the wings 

 may possibly be accounted for by the fact that if the wing be simply 

 pulled off, the parting will in many cases take place all along the 

 line 22, 15, and that in such cases the buzzing continues almost 

 undiminished. 



Test 3. If the vibrations of the alulet be checked by a needle 

 applied at the convexity of the nervure above the point 15, the 

 buzzing continues, though in some instances the pitch of the note 

 is lowered. I will refer later to this alteration of pitch. 



Test 4. — If, whilst the fly is buzzing, the point of a needle be 

 inserted between the percussor 11 and the rib 23, without injuring 

 the parts in any way, the buzzing at once ceases, though the impact 

 of 11 against the needle is quite perceptible. If the needle is placed 

 so that its side rests lightly against the rib 23, the impulses are 

 transmitted through the neeedle and a modified buzzing is produced. 



Test 5. — If a minute spear of tissue paper be inserted between 

 the points 11 and 23, the sound is considerably subdued but not 

 stopped. 



Test (3. — If pins be so placed that, whilst not injuring the 

 wings, they prevent the wings from closing closer than about 



z 2 



