Page:Jardine Naturalist's library Entomology.djvu/311

Rh is necessarily forced through the only openings which present themselves. The more rapid the flight, the greater must be the muscular action, and, consequently, 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 necessarily 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 adhesive 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 attached 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 instrument assumes a great variety of forms in different families to adapt it to their diversified economy; and, in all, exhibits a beautiful example of mechanical contrivance. The members of this interesting order usually