ON INSECT SOUNDS. 245 



In the bees the muscular action is not directly applied to the 

 vibratory organ. The modulation of voice depends here wholly 

 upon increased respiratory efforts. The vocal membranes of bees, 

 drones, hornets, wasps, Xc, are immoveably lixed behind the 

 opening of the stigma. But over the vocal membrane, there is a cup 

 or bell shaped cover of chitinous structure, in the middle of which a 

 fissure opens towards the trachea. Here at this chink, or tissure, 

 an arrangement for closing it is applied consisting of two small 

 projections of chitinised substance which are connected together 

 at their apices by a muscle band. When this muscle contracts the 

 fissure is closed and no air can pass from the tracheae into the 

 vocal cavity. If the insect opens this fissure the air immediately 

 streams out and sets the chords in vibration. This act must be 

 therefore voluntary, and the bee can set its vocal apparatus in 

 action when flying or at rest. 



