SOUND RECEPTION 83 



from the basement membrane of the hypodermis and trachea, border- 

 ing on the blood cavity of the leg. The cells thus stretch between the 

 trachea and this membrane (Fig, 55). This organ is innervated by a 

 purely sensory nerve, the tympanic nerve, originating from the first 

 thoracic ganglion. This nerve also innervates part of the subgenual 

 organ and the intermediate organ. The rest of the subgenual organ is 

 innervated by a branch of the leg nerve. 



The metathoracic tympanic organ of Lepidoptera is the simplest 

 organ of this type. It lies in the anterior wall of a deeply recessed cavity 



Fig. 58. The tympanic organ of the cicada Tibicina haematodes as seen 

 when the abdomen is cut transversely. H, heart; G, gut; A, auditory 

 cavity in which a window has been cut; T, tympanum. (Redrawn from 

 Vogel, 1923.) 



bounded posteriorly by parts of the first abdominal segment (Fig. 56). 

 As in the Acrididae, the membrane is lined with hypodermal epithel- 

 ium plus that of the associated tracheal sac. Two chordotonal sensilla 

 are attached to the inner surface of the tympanic membrane. The 

 axons, forming part of the tympanic nerve, extend anteriorly, receive 

 support en route from a thin ligament, turn at an angle to receive 

 further support from a cuticular projection, the Bugel, then continue 

 on through the tracheal sac ultimately to join the pterothoracic 

 ganglion (Fig. 57). Like the comparable structure in the locust, the 

 nerve is ensheathed in tracheal epithelium. 



