TIIK Ml'SlCAI, Al'l'AKA-ITS. 
83 
As already noUvl, i\\o jj:it"l of soiu;- is riuiiul in the male iiis(Mt onlv. 
and the true sound a[)|)aralus consists of two small ear-hk(« or shell- 
like inflated drums siluat(nl on ihe sidcvs i^{' {\\c hasa! se^uuMit of the 
abdomen. These drums are caused to \il)i-at(* hy the action of pow- 
erful nuiscKv-^, and tlu^ sound is ^•a^iously modified hy adjacent 
smaller disks — the so-called "mirrors" or sonndini: hoards and i->sues 
as the peculiar note of the species, which once beai'd is ue\(M- likelx to 
he forgotten, or. if heard ajj:ain, mistak(Mi for that of somc^ other insect . 
The true sonnd organs are entirely exposed ni the ])erio(lical C'ica«la 
except for tlu^ covering affordetl by the closed wings of the resting 
insect. Tn other cicadas these drums are usually protected b}^ over- 
hipping valves or expansion of the body wall. 
The sounding drum, 
or '^timbal,-' as Reau- 
nuir termed it, of the 
periodical Cicada is a 
tense, dry^crisp mem- 
])rane n u m e r o u s 1 y 
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 
more elastic. The 
sound is produced by 
the rapid \4bration, or 
undid at ion, caused by 
the springing or snap- 
ping in and out of these corrugated drums. Two powerful mux-hvs 
of ver^^ peculiar structure situated wdthin the base of th(^ ab(h)iu(Mi 
set these drums in motion, producing the rattling so-called song of 
the Cicada, very nuich, as has been suggested, as sound is produced 
by pressing up and down the bottom of a tin pan which is sonu^what 
bulged. 
Beneath each ''timbal" in the base of th(^ abdonuMi of th(^ insect 
is a large sound or air chamber, and a third occurs in the thorax 
joining the first two. These are closed by {\\c 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 protect e<l and covered by the semi- 
circular rigid disks projecting from the thorax. These transparent 
Fig. 38.— The musical apparatus of tlie pcrioditul Cicada: a, view 
from beneath, sho\\ing the plates (light colored) covering the 
sounding disks; b, dorsal view, the timbals shoving as light- 
colored areas; c, section at base of abdomen, showing attach- 
ment of large muscles to timbals; (/, timl)al greatly enlarged, 
in normal position; e, same drawn forcil)ly in by the action of 
one of the muscles, as in singing. (Author's illustration.) 
