SOUND RECEPTION 79 



chordotonal organs usually associated with tracheae in other species 

 Some chordotonal organs in the wings of Satyridae are associated with 

 tympana (Vogel, 1912). 



The detailed inner structure of tympanic organs was investigated 

 thoroughly by Schwabe (1906), Eggers (1911, 1919, 1924, 1928), Vogel 

 (1923 a), Hers (1938), Roeder and Treat (1957), and Treat (1959). 

 These studies have been extended by the electron-microscope studies 

 of Gray (1960). 



All tympanic organs have certain features in common. These 

 include: a thin cuticular membrane, a closely appressed internal 

 tracheal sac, and a group of chordotonal sensilla. The sensilla may be 



Fig. 54. Diagram to show the method of attachment of the neural elements 

 to the inner surface of the tympanum of the locust. A, auditory nerve; 

 Fo, fold; Si and S2, location of sense cells; E, elevated process; S, 

 styliform body; L, leg; B, base; D, drum; P, pyriform vesicle; Fi, 

 fusiform body. (Redrawn from Gray, 1960.) 



attached directly in the middle of the tympanum (Acrididae), to its far 

 edge (Cicadidae), or to the trachea instead of the tympanum itself 

 (Tettigoniidae and GrylUdae). They vary in number from two in 

 certain moths to 1,500 or more in cicadas (Figs. 55, 57, 58, 59). 



Of all these, the tympanic organs of Acrididae have undoubtedly 

 been studied in greater detail than any others. The tympanum is a thin 

 (2-3 (J.), imperfectly ovoid area of exocuticle lying in a crater-like 

 depression (sometimes likened to the auditory meatus of the human 

 ear) formed by an incomplete rim of thickened cuticle (Fig. 54). The 

 tympanum is further strengthened circumferentially as a consequence 

 of a thickened cuticular invagination. It is thus a rigidly supported 

 drumhead. It is hned internally, as is almost all cuticula, by a thin layer 

 of hypodermal epitheHum. Closely appressed to the internal side of the 

 tympanum is a tracheal sac fed by a branch from the main trachea 



