THE INTERNAL ANATOMY OF INSECTS 



149 



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



portion of the body- wall (Fig. i66). 



Closely applied to the 

 inner surface of each 

 tympanum (Fig. 167, T), 

 there is a ganglion 

 known as M tiller's organ 

 {go), first described by 

 Miiller (1826). This gan- 

 glion contains many 



Fig. 166. — Side view of a locust with the wings 

 removed; t, tympanum. 



ganglion-cells and scolopalae and is the termination of a nerve extend- 

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

 168 represents a section of Miiller's organ, showing the ganglion-cells 

 and scolopalte. 



Intimately associated with the Miiller's organ are two horny 

 processes (Fig. 167,0 and u) and a pear-shaped vesicle (Fig. 167, hi) ; 

 and near the margin 

 of the tympanimi, 

 there is a spiracle 

 (Fig. 167, St), which 

 admits air to a space 

 inside of the tympa- 

 num, the tympanal 

 air-chamber . 



As the nerve-end- 

 ings in Miiller's or- 

 gan 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 italicus, seen from 

 inner side; T, tympanum; TR, its border; 0, u, two 

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

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

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

 Packard after Graber). 



a. THE CHORDOTONAL 

 ORGANS OF THE 

 TETTIGONIID^ AND 

 OF THE GRYLLID^ 



In the long-homed grasshoppers and in the crickets, there is a pair 

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



