6-6 THE SENSES AND SENSORY ORGANS. 



that much more work is needed before it can be said that these 

 remarkable structures have been satisfactorily worked out. 



b. On the Probable Function of the Tympanic Organs, and their 



Relation to the Halteres. 



Edison's phonograph shows that the same membrane may 

 alternately act as a sound-producing and sound-receiving organ ; 

 and there is no a priori reason for denying such a double func- 

 tion to the tympanic membranes and mirrors in insects ; but 

 I shall endeavour to show that there is much evidence in favour 

 of the view that these membranes are concerned in the per- 

 ception rather than in the production of sounds. 



The existence of sound-receiving tympanic membranes has 

 hitherto been only admitted in the case of certain Orthoptera, 

 the Acrididae and Locustidae. The latter at least possess a 

 complex auditory mechanism. Siebold's and Graber's organs 

 are found highly developed in relation with the tracheal sacs 

 connected with the subgenual or tibial tympana, which cannot 

 be regarded as sound-producing organs, since the sounds are 

 clearly produced by the elytra. 



On the other hand, in the Acrididae (Field Crickets), the 

 tympanic organ is much larger, and only exhibits, so far as is 

 known, Miiller's organ, a group of chordotonal organs situated 

 in a terminal ganglion, which is directly applied to the tympanic 

 membrane. It is further probable that such ganglia exist in 

 relation with the mirrors of the Cicadas, as Swinton affirms [287]. 

 Hence it appears to me far from improbable that the mirrors of 

 the Acrididae, and those of the Cicadse, arc analogous structures. 



Further, the tympanic membranes in the Locustidas, in the 

 (.ryllidae, and the mirrors in the Cicadae, exhibit a chitinised 

 plate which occupies a moiety of the membrane, and I have 

 shown that a similar sclerite exists in my newly discovered 

 txiupanic membrane in the Blow-ily. Whether these mem- 

 luaiics are subgenual, thoracic or abdominal, they exhibit 

 precisely similar peculiarities. There is therefore an a priori 

 argument in favour of a similarity of function. Although the 

 mirrors of the Cicada; are usually regarded as sound-producing 



