Chordotonal organs are arthropod sensory structures consisting of special sensilla called the scolopidia, which are mechano-transducers and respond mainly to stretch or flexion. In insects, they consist of bundles of internal sensilla, each of which has a cap cell, an enveloping cell and one or more sense cells. The distal end of the organ is usually attached to the cuticle of the body wall, marked by a pit, a thickened disc or a nodule of chitin, and the base of the organ is connected with the hypodermis, often by a special ligament. [ http://flybase.org/reports/FBrf0056378.html http://en.wikipedia.org/wiki/Chordotonal_organ ]