104 AUDITORY RODS. 



One of these auditory rods is shown in Fig. 66, 

 and the general arrangement is shown in the subjoined 

 diagrammatic figure (Fig. 67). The rods 

 were first described by Siebold, who con- 

 sidered them to be auditory from their 

 association with the stridulating organs. 

 ..fa They have since been discovered in 

 many other insects, and may be re- 

 garded as specially characteristic of the 

 acoustic organs of insects. They are 

 brightly refractive, more or less elon- 

 gated, slightly club-shaped, hollow (in 

 which they differ from the retinal rods), 

 and terminate, in Graber's opinion,* in 

 a separate end-piece (Fig. 66, ho). In 

 ^?od ^of~^"gS different insects, besides being in some 



hopper, Gryllus -i j i j i • l^ 



viridissimus (a.itQv cascs moro olougated than m others, 

 /J'fluditofy rol\ thev present various minor modifica- 



A:o. terminal piece. ^.^^^ -^ ^^^,^^ ^^^ ^^^ ^^^^-^^ Uuiform in 



size — about '016 mm. ; being as large, for instance, in 

 the young larva of a Tabanus (2 mm. long) as in 

 much larger insects. They are, as we shall see, widely 

 distributed in insects, but as yet unknown in other 

 animals. 



At the upper part of the tibial organ of Ephippigera 

 there is, as already mentioned, a group of cells, and 

 below them a single row (Fig. 65) of cells gradually 

 diminishing in size from above downwards. One can- 

 not but ask one's self whether the gradually diminish- 

 ing size of the cells in the organ of Siebold (Fig. 66) 

 may not have reference to the perception of different 



* Graber, " Die chordotonalen Sinnesorgaue und daa Gelior der 

 InsekteD," Arch, fur Mic. Anat., 1882. 



