36 THE PHYSIOLOGY OF INSECT SENSES 



Five kinds of sensory structures are known to take direct part in 

 proprioception: hair plates, campaniform sensilla, stretch receptors, 

 chordotonal organs, and statocyst-like organs. 



Hair Plates (Position Receptors) 



Concentrations of minute sensilla trichodea similar in general 

 structure to tactile hairs were first described by Lowne (1890) on the 

 anterior part of the thorax of the blowfly (Fig. 26). Similar structures, 

 termed hairplates by Pringle (1938 c), are distributed in the joints of the 

 legs and palpi of cockroaches (Fig. 27). Others occur in the dragonfly 

 and mantis (Fig. 27) (Mittelstaedt, 1950, 1952, 1957) and in the honey- 



FiG. 26. The prosternal organ of Calliphora. B, basal part of head; C, neck 

 sclerite; Co, connecting membrane; N, nerve; P, prothorax. (Redrawn 

 from Lowne, 1890.) 



bee (Lindauer and Nedel, 1959). Single hairs of varying size and shape 

 were found in the body articulations of the cockroach by Diakonoff 

 (1936). Hair plates are undoubtedly a common feature among insects. 

 In all cases the sensilla are stimulated by folds of the intersegmental 

 membrane or contact with adjoining surfaces as the joints are moved. 



The hair plates of the cockroach have been studied in some detail 

 (Markl, 1962; Peters, 1962). The discharge of these receptors is 

 proportional to the degree of bending of the hairs as the joint is 

 flexed. The initial frequency may be 800 or more per second (Fig. 

 29). The rate of adaptation is very slow. Thus, the hair plates act as 

 'position' organs and behave independently of muscular tension. 



The proprioceptive function of hair plates is strikingly illustrated 

 by Mittelstaedt's (1952, 1957) analysis of prey capture by mantids. 

 Successful prey capture is a problem of absolute optic localization. 



