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opening and shutting by turns during the song of the Cicada. 
With regard to the caverns and the subopercular cavities — the 
former perform, in relation to the 44 timbales,” the same role as 
do the subopercular cavities in relation to the mirrors and 
folded membranes. If the abdomen in a living Cicada be 
raised in such wise as to open the above cavities, the sound im- 
mediately increases in intensity, just as when the windows are 
opened in a room in which a musician plays, those outside can 
hear better. If, on the contrary, the abdomen of the same 
insect be depressed, so as to cause it to rest against the oper- 
cula, the sound becomes muffled ; and the same effect is pro- 
duced by the Cicada when free, by suddenly depressing its. 
abdomen after it has been raised, and it is to such oscillations 
of the abdomen that the accentuated song of G.plebeia must be 
attributed. 
About ten years ago, M. Landois, in a most valuable paper on 
the vocal organs of insects,* demonstrated that the 44 timbale ” 
of Keaumur cannot act in the manner described above, since, in- 
stead of being movable by muscular action, it is firmly attached 
to the wall of the metathorax. 44 The song of the Cicada,” he 
concludes, 44 is its voice. This is produced by the air from the 
trachea setting the vocal chords of the metathoracic stigma 
( 4 Schrillstigma ’) into vibration. The shell-like membrane in 
the chitine ring [‘timbale’] and the delicate membranes at 
the bottom of the cavities [ 4 folded membrane ’] are merely 
an apparatus of resonance.” Dr. Paul Mayer, as the result 
of some recent experiments made upon Cicada orni 9 in the 
Zoological Station at Naples, arrives at almost the same con- 
clusions as M. Carlet.” f 
Touching a 46 schema ” of the musical apparatus of the Cicada. 
After studying the mechanism of a physiological apparatus, 
we ought always, thinks M. Carlet, to have in our mind’s eye the 
construction of a physical apparatus which, while reducing 
the first to its simplest expression, nevertheless reproduces the 
principal peculiarities of its action. A schema of the vocal 
organ of the Cicada is easily constructed. A little slip of 
metal is taken, having a groove on its inside edge, and bent in 
the form of the letter U. Into each groove a thin plate of 
steel is next fitted in such wise as to obtain two parallel springs, 
free for half of their length. Before introducing the two plates, 
there should be made in the centre of the outer surface of each 
a slight but permanent depression ; and an instrument is finally 
obtained somewhat analogous to the ubiquitous toy recently 
* Die Ton-und Stimmapparate der Insecten) in) anatomisch-physiologischer 
und akustischer Beziehuny. — 11 Zeitschr fur wissensch. Zoologie,” bd. xvii. s, 
105 j and Taf. xi. figs. 17, 18. 1867. 
f Der Tonapparat der deaden. — Ibid. bd. xxviii. s. 79. 1877. 
