THE FACULTY OF HEARING. 36^ 



The organ of hearing of the locust and cricket species is situate 

 in the front pair of limbs, just under the knee joint. The integu- 

 ment forms here an oval ring spanned by a membrane constituting 

 a tympanum whose surface looks forwards, as this oval drum is 

 placed in the front of the leg, while a smaller circular tympanum 

 is placed at the back. In the Locust a vividissima, and others, the 

 tympanal membrane is covered in part or wholly by overlapping 

 folds of integument. In the cricket it is bare. The principal 

 trachea of the leg expands into a long wide sac, which adheres to 

 the inner surface of the tympanum. The distribution of the nerve 

 apparatus has become more complex than in Acridia. The nerve 

 ends do not run to the tympanal membrane but lie on the tracheal 

 expansion. And the arrangement differs notably in the cricket from 

 that found in the locust. In the former the arrangement is 

 effected by a forking of the nerve into two branches which form 

 a ganglion, at whose distal end terminal processes with imbedded 

 rod-like axial bodies are spread out like a fan on the tracheal sac 

 (lying between it and the tympanum), but rather higher up towards 

 the knee than the tympanal membrane. In the locust there is an 

 additional structure of very striking character. Running down 

 the course of the distended trachea and lying upon it (between the 

 tympanal membranes on either side of the limb), there is seen a 

 gradually lessening band of terminal vesicular-shaped bodies, in 

 the centre of each of which is imbedded a rod-like element, and to 

 each of which runs a fibre of the nerve trunk, which runs by the 

 side of this band at a little distance from it. Each nerve fibril has 

 a small ganglion formed on it just after leaving the main trunk. 

 The whole row of terminal vesicular bodies constitutes what the 

 German anatomists describe as the auditory scala, and each one of 

 them is separately attached by a covering membrane to the 

 expanded tracheal tube which is supposed to act as a resonator 

 (sound chamber.) 



The auditory staves — to give a distinctive name to the rod-like 

 elements of the nerve-ends, which in the Acridia abut on the 



