NO. l8 



SENSE ORGANS OF COLEOPTERA — McINDOO 



57 



scribes them in cerambycid larvae. Hess determined that the pleural 

 discs in these larvae are the points of attachment of abdominal 

 chordotonal organs. Two of Hess's drawings (fig. i8, B and C) were 

 copied to illustrate the internal structure of these organs in coleopter- 

 ous larvae. 



Fig. i8.^ Internal anatomy of so-called auditory organs of beetles. A, draw- 

 ing, two-thirds diagrammatic, from longitudinal sections through second an- 

 tennal segment of an adult Mexican bean beetle, showing Johnston organs con- 

 sisting of groups of sense cells (SC), X Soo. R and C (after Hess), longitudinal- 

 vertical section of the pleural zone and chordotonal ligament from a larva of 

 Ergatcs spiculatus, showing following: AF, axis fiber; C, chitinous cap; CC, 

 cap cell; EC, enveloping cell; EK, end knob; F, fibrils of cap cell; A^, chordo- 

 tonal nerve ; Sc, scolopale ; SC, sense cell ; TL, terminal ligament ; and V, vacuole. 



IV. THIGMORECEPTORS 



1. TACTILE HAIRS 



Hochreuther (25) made a thorough study of the sense hairs on 

 a water beetle (Dytiscns marginalis). On the basis of external 

 structure, he separated them into five divisions. Vom Rath (63, 64) 

 found sense cells connected with all the small hairs on the maxillary 

 palpi of Coccinclla scptcnipunctata, Mclolontha vulgaris, and Tencbrio 



