TYMPANAL SENSE-ORGANS 



289 



ganglion, forms a ganglion (go) upon the tympanum, and terminates 

 in the immediate neighborhood of the labyrinth by a collection of 

 cuneiform, staff-like bodies, with very finely pointed 

 extremities (primitive nerve-fibres ?), which are sur- 

 rounded by loosely aggregated ganglionic globules" 

 (Siebold's Anatomy of the Invertebrates). 



In the green grasshoppers, katydids, and their 

 allies, the ears are situated on the fore tibiae, where 

 these organs can be found after a careful search 

 (Figs. 291, 292). 



The presence of the structure is indicated by the 

 oval disc, the drum, which is a thin tense mem- 

 brane covering the auditory apparatus of nerves, 

 ganglion cells, and auditory rods beneath. 



FIG. 291. Fore 

 tibia of Locusta viri- 

 dissima. id, cover of 

 the drum ; t>; fissure 

 between the drum 

 and its cover. After 

 Graber, from Lang. 



The tympana, or drums, are not present in all Locustidae 

 and Gryllidse, and, as Lubbock states, it is an additional 

 reason for regarding them as auditory organs, that in those 

 species which possess no stridulating organs the tympana 

 are also wanting. In many of the Locustidse the tympana are covered or pro- 

 tected by a fold of the skin projecting over them. These covered ones are, 

 Graber thinks, derived from the open ones. 



On examining the apparatus within the leg under the drum, it is 

 seen to consist of the trachea, the auditory vesicles and rods, gan- 

 glion cells, and acoustic nerve. The trachea is greatly modified 

 (Fig. 292, Tr 1). On passing into the tibia the trachea enlarges and 



cm- 



FIG. 292. A, fore tibia of a European grasshopper (Meconema), containing the ear : Ty, tym- 

 panum or outer membrane; Trl, TV 2, trachea?. B, diagrammatic cross-section through the tibia 

 and ear of the same ; Ty, tympanum ; Ct, cuticula ; CM, hypodermis ; A, the auditory organ con- 

 necting with the tympanum ; B, supra-tympanal auditory organ ; GZ, the ganglion-cell belonging 

 to them ; list, the auditory rod connecting with the ganglion-cells. After Graber, from Judeich 

 and Nitsche. 



divides' into two branches, which reunite lower down. The spiracles 

 supplying the air to this enlarged trachea are considerably enlarged, 

 while in the dumb species it is of the normal size. The enlarged 



