gQ The Fly of Chironomus 



He tells us that wlien a blue-bottle is flying a loud 

 buzz is liearcl. If the wings are held, a note of higher 

 pitch is produced by movements of the abdomen. If 

 such movements are stopped, a note of still higher pitch 

 is given out. 



The lowest of the three notes is due, directly or 

 indirectly, to the vibration of the wings, and ceases 

 when they are held or cut off'. The middle note is 

 caused by vibration of the abdominal rings, which are 

 rubbed against one another from side to side ; the sound 

 may be increased by rubbing the head against the thorax. 

 If the head, legs, wings, and abdomen of an active fly 

 are all removed, so that the thorax is left with no vibra- 

 tile parts except the halteres, the highest note continues 

 to be heard. But if the thoracic spiracles, of which 

 there are two pairs, are choked with gum or wax, the 

 sound ceases. In the blue-bottle both pairs of thoracic 

 spiracles are well developed, but in some other flies 

 one or other pair may be useless for the production of 

 sound. 



By investigating the structure of the spiracles, Landois 

 found that there is an air-chamber just within the 

 external outlet, and that the wall of this chamber is 

 folded, so as to give rise to a number of chitinous 

 laminae, which, he supposes, are caused to vibrate by 

 the forcible drawing of air in or out of the chamber. 

 The laminae are prevented from collapsing by a special 

 vocal ritig, over which the vibrating membrane is 

 stretched. 



The flies of Culicidae can produce during flight the 

 note d". When the wings, legs, and head are removed, 

 they emit a shriller note. There are two pairs of spiracles, 

 of which the hinder pair are the larger. In each spiracle 

 there is a slit-like outlet, a stretched membrane, and an 

 elongate-oval vocal ring. The tension of the ring and 



