62 



SMITHSONIAN MISCELLANEOUS COLLECTIONS 



VOL. y-J 



and sense rods directed away from the point of attachment, free 

 from any connection with the body waU. The crest, however, as 

 pointed out by Schwabe, is not distinctly separated from the inter- 

 mediate organ at its upper end. Both are surrounded by the same 

 membranous sheath, and von Adelung (1892) has shown that there 

 is a cord-Hke strand of fibrous and cellular tissue that connects the 

 intermediate organ with the outer wall of the leg, where it is inserted 

 upon the cuticula between cells of the hypodermis. It seems probable, 

 therefore, that this strand represents the true origin of these organs 



5C1 



Fig. 29. — Sectional views of tympanal chordotonal organ in front leg 

 of Dcctxcus vcrrucivortis. 



A, cross-section of upper end of tibia (simplified from Schwabe, 

 1906) : BC, BC, inner cavity of leg; c, e, outer openings of tympanal 

 cavities {TC, TC) ; other lettering as in fig. 28. The two tracheal 

 branches {aTr, pTr) lie between the tympana (aTin, pTm), with 

 chordotonal crest {Cr) on outer surface of anterior trachea. 



B, diagrammatic cross-section of the crest and a sense cell of the 

 tympanal organ : a, " crest mass " inclosing the sensilla ; aTr, wall of 

 anterior tracheal branch ; CCl, cap cell ; d, distal process of sense 

 cell ; ECl, enveloping cell ; Mb, membrane covering the crest ; Nv, 

 tympanal nerve ; SCI, sense cell ; SR, sense rod, or scolopala. 



in the body wall, and that the position of the crest on the surface 

 of the trachea is a secondary one. 



In the crickets (Gryllidce) only two chordotonal organs have been 

 described in the fore tibise, a subgenual organ, and one on the trachea 

 corresponding with the crest of the Tettigoniidae ; but the latter is 

 shorter and more fan-shaped than in the katydid species that have 

 been studied. (Herbig, 1902; Berlese, 1909.) 



In the Hymenoptera a subgenual chordotonal organ occurs in all 

 the legs of species that have been examined for it, including a saw- 

 fly, ants, wasps of the fainily Vespidse, Bombus, and the honeybee. 

 (Janet, 1904; Schon, 191 1; Mclndoo, 1922). 



