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 tracheje 

 would seem to favour this hypothesis. 



Fig. 68. — Outer part of a section tlirougli the tibia of a Gnjllus viridissimus (after 

 Graberj. h, Hind surface of log; p, wall of trachea; F, fat bodies; Su, snspensor 

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

 connecting the ganglionic ctlls ; E.Sch., end tubes ol: the ganglionic cells, each 

 contaiiiing an auditory rod ; fa, terminal thi-eads of ditto. 



In the true Locustida3 (Acridiodefe of Graber) the 

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

 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- 



