OF INSECTS. 
305 
is necessarily forced through the only openings which 
present themselves. The more rapid the flight, the 
greater must be the muscular action, and, conse- 
quently, the expulsion of the air more violent ; 
conditions which perfectly accord with the various 
degrees of intensity observed in the sounds emitted 
in different states of movement. When a portion 
of the wing is cut off, the rapidity of flight is neces- 
sarily diminished, and the muscles contract but 
feebly, in consequence of the lever which moved 
them being shortened. If the lever be completely 
taken away, which cannot be done without the 
laceration of some of the muscles, the contracting 
power cannot be exercised with sufficient force to 
eject the air, or, in other words, produce sound. 
In accordance with this view, the sound is found 
to be immediately stopped, if the apertures of the 
spiracles be filled up with gum or any other ad- 
hesive substance, and cannot of course be produced 
in whatever state the wings may be. 
The abdomen in hymenopterous insects is often 
very small, and in some extensive tribes it is at- 
tached to the thorax by a very slender segment 
forming a kind of foot-stalk. The most remarkable 
appendage connected with it is the ovipositor, which, 
in most tribes, is very much developed. This in- 
strument assumes a great variety of forms in diffe- 
rent families to adapt it to their diversified economy ; 
and, in all, exhibits a beautiful example of mecha- 
nical contrivance. 
The members of this interesting order usually 
u 
