104 ENTOMOLOGY 
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The well-known “ shrilling”’ of the male cicada is produced 
by the rapid vibration of a pair of membranes, or drums, sit- 
uated on the basal abdominal segment, and vibrated each by 
means of a special muscle. 
Frictional sounds are made by beetles in a great variety of 
ways: by the rubbing of the pronotum against the mesonotum 
(many Cerambycidze) ; or of abdominal ridges against elytral 
rasps (Elaphrus, Cychrus); or two dorsal abdominal rasps 
against specialized portions of the wing folds (Passalus cor- 
nutus), not to mention other methods. In most cases one 
part forms a rasp and the other a scraper, for the production 
of sound. 
In many of these instances the sound serves to bring the 
two sexes together and is not necessarily confined to one sex; 
thus, in Passalus cornutus both sexes stridulate. 
A few moths (Sphingide) and a few butterflies make 
sounds; the South American butterfly A geronia feronia emits 
a sharp crackling noise as it flies. A rasp and a scraper have 
been found in several ants, though ants very seldom make any 
sounds that can be distinguished by the human ear; JMutzlla, 
however, makes. a distinct squeaking sound by means of a 
stridulating organ similar to those of ants. 
Stridulating organs attain their best development in Orthop- 
tera, in which group the ability to stridulate is often restricted 
to the male, though not so often as is commonly supposed. 
Among Acridiidz, Stenobothrus rubs the hind femora against 
the tegmina to make a sound, the femur bearing a series of 
teeth, whieh scrape across the elevated veins of the wing-cover ; 
while the male of Dissosteira makes a crackling sound during 
flight or while poising, by means of friction between the front 
and hind wings, where the two overlap. 
Locustidze and Gryllidze stridulate by rubbing the bases of 
the tegmina against each other. Thus in the male Microcen- 
trum laurifolium the left tegmen; which overlaps the right, 
bears a file-like organ of about fifty-five teeth (Fig. 136), while 
the opposite tegmen bears a scraper, at right angles to the file. 
