THE MUSICAL APPARATUS. 83 
As already noted, the gift of song is found in the male insect only, 
and the true sound apparatus consists of two small ear-like or shell- 
like inflated drums situated on the sides of the basal segment of the 
abdomen. These drums are caused to vibrate by the action of pow- 
erful muscles, and the sound is variously modified by adiacent 
smaller disks—the so-called ‘‘mirrors”’ or sounding boards—and issues - 
as the peculiar note of the species, which once heard is never likely to 
be forgotten, or, if heard again, mistaken for that of some other insect. 
The true sound organs are entirely exposed in the periodical Cicada 
except for the covering afforded by the closed wings of the resting 
insect. In other cicadas these drums are usually protected by over- 
lapping valves or expansion of the body wall. 
The sounding drum, 
or ‘‘timbal,”’ as Réau- 
mur termed it, of the 
periodical Cicada is a 
tense, dry, crisp mem- 
brane numerously 
ribbed or plated with 
the convex surface 
turned outward. The 
ribs are chitinous thick- 
enings or folds in the 
surface of the parch- 
ment -like drum, and 
strengthen the drum 
while perhaps render- 
ing it at the same time 
é Fig. 38.—The musical apparatus of the periodical Cicada: a, view 
more elastic. The trom beneath, showing the plates (light colored) covering the 
sound is produced by sounding disks; 6, dorsal view, the timbals showing as light- 
: : : colored areas; c, section at base of abdomen, showing attach- 
the rapid vibration, or ment of large muscles to timbals; d, timbal greatly enlarged, 
undulation caused by in normal position; ¢, same drawn forcibly in by the action of 
a a one of the muscles, asin singing. (Author’s illustration.) 
the springing or snap- 
ping in and out of these corrugated drums. Two powerful muscles 
of very peculiar structure situated within the base of the abdomen 
set these drums in motion, producing the rattling so-called song of 
the Cicada, very much, as has been suggested, as sound is produced 
by pressing up and down the bottom of a tin pan which is somewhat 
bulged. 
Beneath each “‘timbal”’ in the base of the abdomen of the insect 
is a large sound or air chamber, and a third occurs in the thorax 
joining the first two. These are closed by the body walls and mem- 
branes, and the two abdominal ones beneath by the very peculiar 
‘‘mirrors,”’ or ‘‘spectacles’’—-the tense, mica-like membranes situated 
at the base of the abdomen and protected and covered by the semi- 
circular rigid disks projecting from the thorax. These transparent 
