266 HANDBOOK OF INVERTEBRATE ZOOLOGY. 



spiracle is the thickest, and its inner face is covered by a 

 mass of spherical pigmented cells. 



7 . Near the centre of the tympanum there is a much 

 thinner, nearly circular space, near the centre of which 

 there is a triangular chamber (^•) or cavity hollowed out 

 in the substance of the tympanum. 



8. From this chamber a tube (Ji) runs towards the 

 spiracle, and opens internally near the letter ^, from which 

 point the tube is continued for a short distance as an open 

 channel (c). 



9. At e, near the end of this channel, the tympanum is 

 greatly thickened and folded upon itself so as to form a 

 hollow, cone-shaped prominence (e), which projects from 

 the inner surface of the tympanum, while its cavity opens 

 on the outer surface at g. 



10. Below this prominence the tympanum is folded so 

 as to form a channel (g^^. 



11. Soon after it enters the ear cavity the auditory 

 nerve (?) expands to form the bell-shaped auditory gan- 

 glion (m), which rests upon one side of the cone-shaped 

 prominence (e), and is also continued upwards and down- 

 wards around the prominence. Below the prominence the 

 ganglion gives rise to a small nerve, which passes into the 

 channel c, and then enlarges to form an accessory gan- 

 glion (^), and passes from this through the tube (h) to the 

 triangular chamber (h) , where it enlarges to form a small 

 triangular ganglion, which may be called the tympanic, 

 since it is entirely surrounded by the chitin of the tym- 

 panum, except at the point where the nerve joins it. 



The microscopic structure of the ganglia appears to vary 

 somewhat in the different genera of the family. In Steno- 

 bothrus (according to Schmidt, Arch. f. Mik. Anat. xi. 

 195) fine fibres radiate from the tympanic ganglion and 



