THE 1NTERX.IL STRUCTURE OF ANTS. 



structures, which are present in a great many insects, even in the larval 

 stages, are typically compact, spindle-shaped bundles of sensillae, each 

 consisting of a chitin-secreting gland and a nerve cell. These cells are 

 arranged in a series at an angle to the integument and are stretched, 

 like a tendon, across a cavity between opposite points in the cuticle, or 

 between a point in the cuticle and some internal organ. The gland 

 cell secretes and retains within its cytoplasm a peculiar cone or rod. 

 known as the scolopal body. The chordotonal organs are supposed to 

 be auditory in function, because they are most elaborately developed in 

 the stridulat-ing Orthoptera (crickets and katydids), and because their 

 structure would seem to 

 be adapted to respond- 

 ing like the chords of a 

 musical instrument to 

 delicate vibrations. Tn 

 ants the development of 

 these sense-organs is 

 greatly inferior to that 

 of the Orthoptera just 

 mentioned, but they are 

 nevertheless very easily 

 seen when one knows 

 exactly where to look 

 for them. They were 

 first detected by Lub- 

 bock ( 1877) in the 

 proximal portion of the 

 fore tibia? of Lasius 

 flavus, Mynnica i'ngi- 

 nodis and Pheidolc me- 

 gacephala. He pointed 

 out their resemblance to 

 the subgenual chordo- 

 tonal organs of Orthop- 

 tera, discovered by von 

 Siebold in 1844, but al- 

 though he fancied he could discern some of their minute structure, 

 his account and figure are very primitive. The matter was re-investi- 

 gated by Graber (1882), who found the organs in Solenopsis, Myrme- 

 cina and Tetramorium, and showed that they occur not only in the 

 fore but also in the middle and hind tibiae, that they contain scolopal 

 bodies and are also in other respects typical chordotonal organs. 



FIG. 33. Chordotonal organs in tibiae of Myrmica 

 rubra worker. (Janet.) A, Longitudinal section of 

 fore tibia ; B, cross-section of same ; C, cross-section 

 of middle tibia ; D, cross-section of hind tibia ; a. 

 chordotonal organ ; b, internal fossa ; c, small ; d. 

 large trachea ; e, nerve ; /. muscle ; g. septum ; h, 

 scolopal bodies ; i, ganglion cells ; k, distal nuclei. 



