4.00 NOISES OF INSECTS. 
They begin their song—which is a short chirp regularly 
interrupted, in which it differs from that of the Locusta 
—long before sun-rise. In the heat of the day it is in- 
termitted, and resumed in the evening. This sound is 
thus produced:—Applying its posterior shank to the 
thigh, the animal rubs it briskly against the elytrum’*, 
doing this alternately with the right and left legs, 
which causes the regular breaks in the sound. But 
this is not their whole apparatus of song—since, like 
the Tettigonize, they have also a tympanum or drum.” 
De Geer, who examined the insects he describes with 
the eye of an anatomist, seems to be the only entomo- 
logist that has noticed this organ. On each side of 
the first segment of the abdomen,” says he, “ immedi- 
ately above the origin of the posterior thighs, 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 by a 
wrinkled flexible membrane. The opening left by this 
operculum is semi-lunar, and at the bottom of the cavity 
is a white pellicle of considerable tension, 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 re- 
sistance. When the pellicle is removed, a large cavity 
appears. In my opinion this aperture, cavity, and 
above all the membrane in tension, contribute much to 
produce and augment the sound emitted by the grass- 
hopper®.” ‘This description, which was taken from the 
migratory locust (G. migratorius, L.), answers tolerably 
2 De Geer, iii, 470. baba. (Meta exiles 2. a. 
