POSSIBLE STRIDULATING ORGAN IN THE MOSQUITO. 369 



B, and we think that this movement of these two ridged surfaces, one on the other, 

 is responsible for some of the characteristic buzzing of the mosquito. 



The exact cause of the note of a mosquito has been a matter of much dispute. The 

 following extract from a paper published last January by one of us, in collaboration 

 with Dr G. H. F. Nuttall, describes some experiments made last year at Cambridge on 

 this subject : — 



' According to Howard * the sound during flight is " apparently produced, as with 

 ' flies and other dipterous insects, not by the rapid vibration of the wings, but by the 

 ' vibrations of a chitinous process in the large tracheae just behind the thoracic spiracles. 

 ' These vibrations are produced by the air during respiration." He furthermore states 

 ' that the sound produced in its flight is higher in Culex than it is in Anopheles, adding 

 * that " the villain in the play has usually a bass voice." 



1 Our experiments do not support Howard's assertion with regard to the wing not 

 ' producing a note, for we have found by cutting off more and more of the wing that 

 ' the sound decreased in volume, the note rising progressively. When the wing was cut 

 1 off quite closely, a very high-pitched note of slight intensity remained, this, as we 

 'supposed, being produced by an internal apparatus such as Howard indicates. It may, 

 ' however, be due to respiratory movements which are exaggerated through the efforts 

 ' at flight. The sound is not produced by the insect in repose. We found that the males 

 ' gave a higher-pitched note than the females, and that the note was higher in both 

 ' sexes when they had fed ; the greater the meal, the higher the note. Of four unfed 

 ' females, three gave notes within a quarter of a tone of 264 {i.e. of 240 to 270 vibra- 

 ' tions), the fourth female gave an abnormally low note of about 175 vibrations. Four 

 ' other females were arranged in the order of the distension of the abdomen by food, 

 ' the last being largely distended ; these gave notes corresponding roughly to 264 — 281 

 ' — 297 — 317 vibrations, or according to the musical scale, the notes : 



i 



te 



' Three unfed males gave exactly the same note, viz. corresponding to 880 vibra- 



' tions gg= =§ ; immediately after feeding one gave the note Af, another which had fed 



' well BR. The unfed males were more closely concordant than the unfed females, the 

 ' latter varying over about a semitone. Mr J. W. Capstick, M.A., Fellow of Trinity 

 ' College, Cambridge, to whom we are greatly indebted for making these ear determina- 

 ' tions for us by means of tuning-forks, was not certain that the note given by the 

 ' males was not one of 440 vibrations. Overtones were obviously strong, and it sounded 

 ' at times as if there were a faint note of 440 vibrations overshadowed by a strong one 

 ' of 880. 



* Mosquitoes, by L. O. Howard. New York : M'Clure, Phillips & Co., 1901, p. 14. 



