INSECTA 



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cell, to one end of which is attached a nerve fibre. To the other end 

 is connected a rod or scolopale which ends in an apical thickening or is 

 free to vibrate in the fluid protoplasm of an enveloping cell. The 

 whole structure is attached to the hypodermis by covering cells at 

 one end and by a ligament at the other (Fig. 315 D). 



Fig. 315. Insect sensillae. A, Trichoid sensilla. B, Placoid sensilla. C, Coelo- 

 conic sensilla. Tc. trichogenous cell; He. hair-membrane cell; Nc. nerve 

 cell. D, Chordotonal sensilla. Cc. cap cell to scolopale ; Ec. enveloping cell ; 

 Ek. end knob of scolopale; H. hypodermis; L. ligament of attachment; 

 Nc. nerve cell; S. scolopale and V. its fluid filled vacuole. A, modified 

 from Eltringham after Snodgrass. B, modified from Imms after Hess. C and 

 D from Imms. 



Scolopale sensillae of this type may or may not be associated with 

 a tympanum or ear drum. When they are, as in cicadas and grass- 

 hoppers, there is clear evidence of response to sound waves set up by 

 sound-producing organs possessed by themselves. 



