MECHANORECEPTION 67 



control lift and to stabilize reflexly in all three planes of rotation, that 

 is, to correct for pitch, yaw and roll. In insects with four wings much of 

 the required information derives from mechanoreceptors on the wings. 

 As a result, changes in pronation, supination, and angle of attack of 

 the wings are made until stable flight is achieved. Details of the res- 

 ponse characteristics of the various sensory structures of the wing, 

 however, are poorly known. 



More information is available about the halteres of Diptera. These 

 structures, homologues of the hind wings, are radically specialized as 

 balancing organs. They are lavishly equipped with all types of 

 mechanoreceptors whose homologies can be traced to those of the 

 wings of non-dipterous insects (Pflugstaedt, 1912; Zacwilichowski, 

 1936). Essentially, each is a heavy mass of tissue on the end of a thin 

 stalk. The folding of the base is very complicated, consisting of a main 

 hinge and a condyle of secondary articulation (Fig. 45) (Pringle, 1948). 

 In these regions are concentrated, in Calliphora, for example, about 

 418 mechanoreceptors. They include the following sensilla as des- 

 cribed by Pflugstaedt (1912) : 



Campaniform Sensilla 



Dorsal scapal plate 

 Ventral scapal plate 

 Basal plate 

 Dorsal Hicks papillae 

 Ventral Hicks papillae 

 Undifferentiated papilla 



Chordotonal Sensilla 



Large chordotonal organ 

 Small chordotonal organ 



All but thirty-five are located in the three plates and the large chordo- 

 tonal organ. It is significant that the axons from these sensilla do not 

 fuse as is the case with the campaniform sensilla in the palps of the 

 cockroach (Pringle, 1938 b, 1948). The arrangement of sensilla is 

 basically the same in all families of Diptera (Brauns, 1939). It has been 

 suggested (Pringle, 1948) that strains produced by vertical oscilla- 

 tion of the haltere are detected by the dorsal and ventral scape plates, 

 the dorsal and ventral Hicks papillae, and the small chordotonal 

 organ. Strains produced by gyroscopic torques are presumed to be 

 detected by sensilla of the basal plate and the large chordotonal organ. 



