Phonoreception 



493 



it should not be assumed that phonoreception is completely unimportant 

 in the life of other arthropods. 



The phonoreceptors of insects are of two general types: (1) the tympanic 

 organs, and (2) hair sensilla. The tympanic organs are highly specialized 

 structures which are xery sensitive as receptors, especially for high frequen- 

 cies. Howe\er, it is well known that insects which possess no tympanic 

 organs are sensiti\e to sound, especially to low frequencies, and this sensi- 

 tivity is localized in hair sensilla. 



Morphology of Tympanic Organs. A tympanic organ consists of a thin 

 region of the exoskeleton which acts as a tympanic membrane, an underlying 

 air sac, and the sensory elements known as a chordotonal organ or scolopid- 

 ium. Tympanic organs are paired structures which occur in the Orthoptera, 



Fig. 169. Tympanal organs in the tibia of Locustids. A, Locusta foreleg, showing the 

 slit openings of the tympanal sacs (after Weber'"'). B, Transverse section of anterior tibia 

 of Dectycus, through the tympanal organ (after Schwabe*')- c> opening on surface of 

 tibia; b, blood channel; c, tympanal cavities; d, tracheae; e, blood channel with muscles 

 and nerves; f, tympanum; g, rigid wall between the enlarged tracheae; Ji, crista acoustica, 

 showing one chordotonal organ; i, sense cell. From Wigglesworth.* 



Hemiptera, and Lepidoptera. Among the Lepidoptera they occur only in 

 the Noctuoidea, Geometroidea, and Pyralidoidea, and they are found either 

 in the forepart of the abdomen or in the metathorax of the adult. Among 

 Hemiptera they are probably functional only in adult Cicadidae, in which 

 they occur in the abdomen. Among Orthoptera they are found in most 

 species of Acridiidae, Tettigoniidae, and Gryllidae. In grasshoppers they 

 occur in the abdomen, and in katydids and crickets they occur near the 

 proximal end of the tibiae of the first pair of legs. They are present in late 

 nymphal instars but probably are functional only in adults. 



