86 
ORGANS OF SOUND. 
trachea, and this comes into action on the contraction 
of the muscle actuating the apparatus, during respira- 
tion as well as in the production of sounds. By the 
closing of the tracheae the passage of air from these 
to the outside is entirely shut off, and during expira- 
tion the stream of air to the outside can be regulated 
and made to pass over the edges of the folded mem- 
brane, and the sounds are produced in a manner 
similar to that of a bugler, who produces different 
sounds by blowing through his lips into the mouth- 
piece of his instrument. 
The mechanism by which the closing of the 
trachea is effected consists of a double lever formed 
of two unequal cones {a and b), connected by a trans- 
verse muscle, and placed at the two extremities of 
the obturator tendon (c). This muscle, called obtur- 
ator nmscle.^ seen stretched from a to b, in contracting, 
causes it, as well as the tendon, to act on the stirrup 
(^), which closes the trachea at the will of the insect. 
Landois (88) found that by stopping the openings 
of the spiracles with wax, humming ceases, or becomes 
so feeble that it is hardly perceptible. The reason 
is easily explained if we bear in mind the structure 
of the spiracles. He considers the spiracular notes 
to be due principally to the large meta-thoracic 
spiracles, and that the abdominal ones may also assist 
in their production. 
Baron von Berlepsch (3), Pollmann (134), and 
others have described the various sounds produced. 
Stahala has given to the sounds different meanings. 
For instance, he says that, if in winter one taps the 
