CHORDOTONAL SENSE-ORGANS 



291 



of these vesicles is connected with- the nerve by a fibril (Fig. 29.S, 

 vN), and contains an auditory rod (Fig. 294). They are said by 

 Graber to be brightly refractive, hollow (thus differing from the 

 retinal rods, which are solid), and terminate in a separate end-piece 

 (ko). The rods were first discovered by Siebold, and, as Lubbock 

 remarks, may be regarded as specially characteristic of the acoustic 

 organs of insects. 



As will be seen in Fig. 293, at the upper part of the tibial organ of Ephippi- 

 >-era there is a group of cells, and below them a single row of cells gradually 



~uiv 



vv 



FK;. 295. Chordotonal organ in nymph of 

 a white ant. After Muller, from Sharp. 



diminishing in size from above down- 

 wards. "One cannot but ask oneself," 

 says Lubbock, "whether the gradually 

 diminishing size of the cells in the organ 

 of Siebold may not have reference to the 

 perception of different notes, as is the 

 case with the series of diminishing arches 

 in the organ of Corti of our own ears." 



These organs were supposed to be 

 restricted to the Orthoptera, but in 1877 

 Lubbock discovered what seems to resem- 

 ble the supra-tympanal auditory organ 

 of Orthoptera in the tibia of the yellow 

 ant (Lasius flavus). Graber confirmed 

 Lubbock' s account, and also discovered 

 these organs in the tibia of a Perlid 

 (Isopteryx apicalis), and Fritz Muller has 

 detected them in the fore tibiae of the 

 nymph of Calotermes rugosus (Fig. 295). 

 To these structures Graber gave the name 

 of chordotonal organs. 



He has also detected these organs in all 

 the legs of other insects (Trichoptera, 



Pediculidse), and auditory rods have been discovered in the antennae of Dyticus 

 and of Telephorus by Hicks, Leydig, and Graber. Graber classifies the chordo- 

 tonal organs into truncal and membral. In Coleoptera and Trichoptera they 

 may occur on several joints of the leg ; others are more localized, thus he dis- 

 tinguishes femoral (Pediculidse), tibial (Orthoptera, Perlidse. Formicidse), and 

 tarsal organs (Coleoptera). 



A type of chordotonal organ, observed in the body-segments of the larvae of 

 several insects by Leydig, Weismann, Graber, Grobben, and Bolles Lee, is to 

 be seen in the transparent larva of Corethra (Fig. 296), where the auditory 

 organ extends to the skin. It contains at the point cs two or three auditory 



FIG. 296. Right half of 8th body-seg- 

 ment of Corethra plumicornis : g, ganglion 

 of ventral cord ; Im, longitudinal muscle ; 

 en, chordotonal nerve ; el, chordotonal liga- 

 ment ; eg, chordotonal ganglion ; cs, rod of 

 chordotonal organ ; cat, terminal cord ; tb, 

 tactile setae ; hn, out-going fibres of the in- 

 tegurnental nerves. After Graber, from 

 Lang. 



