MECHANORECEPTION 63 



muscles being compound ones (Bccht, 1959) and because of the large 

 number of mechanoreceptors (tactile hairs, hair plates, campaniform 

 sensilla, chordotonal sensilla) and their complicated innervation 

 (Nijenhuis and Dresden, 1952; Dresden and Nijenhuis, 1958). That 

 the situation is indeed complicated is further suggested by the detailed 

 cinematographic studies of Hughes (1952, 1957) on normal cock- 

 roaches and amputees. As various legs are amputated, the mechanical 

 aspects of walking change. There is a corresponding change in proprio- 

 ceptive feedback, with the result that gait and other aspects of walking 

 are altered. 



In the stick insect (Carausius morosus) the posture in walking is 

 regulated by feedback control via hair plates which measure the angle 

 between the coxa and trochanter-femur (Wendler quoted by Mittel- 

 staedt, 1961). In the normal insect the body is held free from the 

 ground as a result of this feedback. The distance above the ground 

 remains the same even when the insect is carrying four times its weight. 

 If the sense organs are eliminated the insect touches the ground under 

 its own weight. 



Flying 



Flight, of all forms of locomotion, is the most demanding of infor- 

 mation. Whether one believes that the basic co-ordination of flight is 

 an inherent function of the central nervous system modulated by sen- 

 sory feedback (Wilson, 1961) or that flight is more exclusively a matter 

 of reflex control (Weis-Fogh, 1956; Pringle, 1957), it is certain that its 

 initiation, maintenance, adjustment, and termination can be effected 

 by means of elaborate sensory mechanisms. A brief survey of the prob- 

 lems involved will indicate the role of the mechanical senses. A com- 

 plete treatment is given by Pringle (1957). 



The most specific and universal reflex for initiating flight is the 

 'tarsal reflex' originally described by Fraenkel (1932). When the feet of 

 most insects are removed from the substrate, flight commences. (There 

 is a similar reflex in giant water bugs, Lethocerus americanus and 

 Benacus griseus, whereby breaking of contact with the substrate ini- 

 tiates swimming movements [Dingle, 1961].) So essential to flying 

 insects is this reflex that in some species (Phormia, Calliphora, Vespa) 

 amputation of the legs interferes with the ability to cease flying. Con- 

 versely, contact with the substrate terminates flight. The electro- 

 physiological studies of Pringle (1938 b, 1940), have shown that at 

 least in Periplaneta the principal receptors involved are sensilla 

 campaniformia on the trochanter and femur. On the other hand. 



