106 EAR OF LOCUSTS. 



vibrations may be communicated to the nerve : either 

 the vibrations of the tympanum may act upon the 

 air in the tracheae, and so upon the auditory rods, or 

 the air in the tracheae may remain passive, and the 

 vibrations may act upon the auditory rods through the 

 fluid in the anterior chamber of the leg. The fact 

 that the auditory rod is turned away from the tracheae 

 would seem to favour this hypothesis. 



Fig, 68.— Outer part of a section through the tibia of a Gryllus viridissimus (after 

 Graber). h, Hind surface of leg; p, wall of trachea; jP, fat bodies; Su, suspensor 

 of the trachea; vW, tracheal wall; TN, nerve; gz, ganglionic cells; rB, tissue 

 connecting the ganglionic cells; E.Sch., end tubes of the ganglionic cells, each 

 containing an auditory rod ; fa, terminal threads of ditto. 



In the true Locustidae (Acridiodeae of Graber) the 

 organ of hearing is situated, not in the anterior tibiae, 

 but in the first segment of the abdomen ; externally it is 

 marked by a glistening appearance, and it is oval, or in 

 some cases nearly ear-shaped. It was first noticed by 

 Degeer. Behind the tympanum is a large tracheal sac, 

 as in the families already described, and the tension of 

 the tympanum is regulated by one, or in some cases by 

 two muscles. The tympanum also presents two chitin- 



