THE INTERNAL ANATOMY OF INSECTS 



149 



Fig. 1 66. Side view of a locust with the wings 

 removed; /, tympanum. 



part of these organs, the tympanum, is conspicuous, being a thinned 

 portion of the body- wall (Fig. 166). 



Closely applied to the 

 inner surface of each 

 tympanum (Fig. 167, T), 

 there is a ganglion known 

 as Muller's organ (go), 

 first described by Muller 

 (1826). This ganglion 

 contains many ganglion- 

 cells and scolopalae and is the termination of a nerve extending 

 from the central nervous system, the auditory nerve (). Figure 

 1 68 represents a section of Muller's organ, showing the ganglion -cells 

 and scolopalse. 



Intimately associated with the Muller's organ are two horny 

 processes (Fig. 167, o and u) and a pear-shaped vesicle (Fig. 167, bi); 

 and near the margin 

 of the tympanum, 

 there is a spiracle 

 (Fig. 167, si), which 

 admits air to a space 

 inside of the tympa- 

 num, the tympanal 

 air-chamber. 



As the nerve-end- 

 ings in Muller's organ 

 are attached to the 

 tympanum, it is a 

 chordotonal organ 

 of the integumental 

 type; it is attached 

 to a vibratile mem- 

 brane, between two 

 air-spaces. 



Fig. 167. Ear of a locust, Caloptenus if aliens, seen from 

 inner side; T, typmanum; TR, its border; o, u, two 

 horn-like processes; bi, pear-shaped vesicle; n, audi- 

 tory nerve; ga, terminal ganglion or Muller's organ; 

 st, spiracle ; M, tensor muscle of the tympanum (From 

 Packard after Graber). 



d. THE CHORDOTO- 

 NAL ORGANS OF THE 

 LOCUSTID.E AND OF 

 THE GRYLLID^E 



In the long-horned grasshoppers and in the crickets, there is a pai r 

 tympana near the proximal end of the tibia of each fore leg. In 



