472 PHYSIOLOGY. 



but he did not clearly comprehend its true mechanism * during chirp- 

 ing. Joh. Muller has latterly described it as an auditory organ f . 



It is in the family of the Cicada, namely, the larger ones (Tetligonia, 

 Fabr., Cicada, Lat.) that the voice attains its highest degree. In 

 these creatures also we find the voice possessed exclusively by the 

 males, and it is produced by an organ that has the greatest resem- 

 blance to that of the Grylli. In these it is also an elastic membrane, 

 which is longitudinally folded and stretched over an oval horny ring 

 seated immediately behind the first large spiracle of the abdomen, 

 which, by a peculiar muscular apparatus, is made to vibrate. To each 

 of these elastic membranes a strong conical muscle runs, which, with 

 its broad basal surface, is attached to a plate-shaped horny tendon, the 

 short pedicle of which is in connexion with the drum, and which ori- 

 ginates at a central, furcate, horny process of the ventral plate of the 

 second abdominal segment, the analogue of the furcate process of the 

 breastplates. This muscle, together with the membrane, constitutes 

 the vocal organ. If the abdomen, by the respiratory motion, be expanded 

 or contracted, this muscle likewise stretches, whereby the membrane is 

 made to vibrate, and consequently resound. The sound is increased, as 

 in the Grylli, by means of a large air bladder, which lies at the lateral 

 portion of the abdomen, and which closely covers the muscle as well as 

 the membrane. In this cavity the sound rebounds, and thus proceeds 

 more strongly from the insect. As external organs, there are, in addi- 

 tion to this vocal organ, some other parts which serve as a cover to it, 

 but which are not of importance to the production of the voice, namely, 

 two half circular horny plates, which spring from the margin of the 

 horny integument in front of the drum, and more or less cover it ; also 

 beneath the drum in the centre of the ventral plate of the segment 

 behind the coxa? of the posterior legs there are two small, oval, trans- 

 parent fenestrations filled by a tense membrane, but which likewise 

 appear to stand in no direct causal connexion with the voice. In the 

 female also these little fenestrations are found, although less perfect, as 

 well as the external valves which cover the drum ; but there is not the 

 least trace of this itself, nor of the muscle which moves it. The air- 

 bladder the female likewise possesses, but it is smaller than in the 

 male J. 



* M&noires, vol. iii. p. 471, PI. XXIII. f. 2 and 3. 

 + Zur vergl. Physiol. tier Gcsichtssinnc, p. 438. 



* Compare, upon this vocal organ, the Treatise of Cams in the Analektcn zur Natiu- 

 \vii i -cn>cliatt uiul llcilk uncle. Dresden, lci'29. ftvo. p. 151. 



