LETTERS ON ENTOMOLOGY. 115 
The grasshopper tribes, or gryllidce, and the 
Cicada (iettigonia) , are chiefly remarkable for the 
noise or chirping they make ; which however is 
confined to the males, as the females are quite mute. 
The common grasshopper produces his morning 
and evening song by applying his posterior shank 
to the thigh, and rubbing it briskly against the 
elytrum, or wing-case; this it does alternately 
with the right and left legs : they have also a 
tympanum or drum. De Geer thus describes it : 
On each side of the first segment of the ab- 
domen, immediately above the origin of the 
hind legs, there is a considerable and deep 
aperture of rather an oval form, which is partly 
closed by an irregular flat plate, or operculum, 
of a hard substance, but covered with a wrinkled 
flexible membrane. The opening left by this 
operculum is crescent-shaped, and at the bottom 
of the cavity is a white skin tightly stretched over, 
and shining like a little mirror. On that side 
of the aperture, which is towards the head, there 
is a little oval hole into which the point of a pin 
may be introduced without resistance. When 
the pellicle is removed, a large cavity appears. 
This description, which is that of the migratory 
locust (gryllus migratorius), answers very well 
to the tympanum of the common grasshoppers 
