ORGANS OF SOUND. 
85 
restris^ hortorum.^ or lapidarius., be shut up in a box, a 
loud and violent humming, the sign of anger or fear, 
will be heard, even if the wings are only producing a 
slight tremulous motion. 
The wings are only one cause of sound, and pro- 
duce the buzzing, but the humming is due to an 
apparatus connected with the spiracles and tracheae. 
The spiracles, specially studied and described by 
Krancher (84) in this connexion, of which Fig. 37 is 
a representation, showing the 
apparatus called by Straus- 
D u rck h eim (157) epiglottis 
(epiglotte), have their me- 
chanism hidden beneath the 
outer skin. The opening to 
the spiracle is seen at and 
communicates with the out- 
side, being covered with 
hairs to prevent the access 
of dust. This leads to an 
enlargement at the com- 
mencement of the trachea and immediately behind 
the spiracles, called the stigmatic vestibule.^ which 
acts as a sounding box, and plays an important 
part in increasing sound. A folded membrane (/), 
* called the vocal memhra?ie^ and forming the lips, or 
curtains, more or less plaited and fringed, is placed 
between the edges of the spiracle \g) and the sounding 
box, which, vibrated by the air, produces a different 
sound according to its tension. .-\t the end of this 
enlargement there is an apparatus for closing the 
Fig. 37 -— 
