76 THE PHYSIOLOGY OF INSECT SENSES 



shearing forces on the whole organ. When the bee is crawHng down a 

 vertical surface the head will incline dorsally and the dorsal areas of 

 the hair plate will be maximally stimulated. When a bee on a vertical 

 surface turns to the right or left the hair plates on different sides of the 

 thorax will be unequally stimulated. In this mechanism there is 

 potentially a very fine capacity for analysing the position angle on the 

 vertical plane. The degree of bending of individual hairs and the 

 spatial distribution of bend in the hair plates as a whole could provide 

 the necessary information (Lindauer, 1961). Severing the nerves to 

 these organs, immobilizing the head, or changing the centre of gravity 

 of the head by weighting it results in impairment of responses to 

 gravity and ability to orient communication dances correctly with 

 respect to gravity. The hair plates at the articulation of the thorax 

 and abdomen function in a similar fashion. They appear to be subord- 

 inate to the cervical organs, however, because they alone are unable to 

 regulate responses to gravity when the cervical organs are eliminated 

 or when the head is fixed or weighted. 



A comparative study of the occurrence and structure of hair plates 

 at the joints of representatives of five famihes of ants, the honeybee, 

 and Vespa saxonica has shown that these setal fields occur at the 

 antennal, cervical, petiolus, and gaster joints and on the joints 

 between the thorax and coxae and coxae and trochanters (Markl, 

 1962). By removing sense organs, disconnecting the various joints, 

 or cementing the joints in abnormal positions, Markl was able to 

 demonstrate that the cervical hair plates are the most important for 

 gravity reception. The others in decreasing order of importance are 

 the petiolus, the antennal, the coxal, and the gaster. In agreement 

 with Vowles (1954) it was found that the antennal organs serve as 

 gravity receptors but they represent only one, and by no means the 

 most important, receptor system for gravity. In supplementing the 

 results of Lindauer and Nedel (1959) it was shown that the receptors 

 at the coxal joints but not those of the antennae serve for gravity 

 reception in the honeybee. Since the hair plates are able to perceive 

 active movements of the joints, it is argued that multiple development 

 of hair plates is necessary if these organs are to serve as gravity 

 receptors. Only a message in the same direction from one or more of 

 the hair plates is related to gravity by the central nervous system, 

 whereas aberrant responses from one or more areas are interpreted 

 as joint movement independent of gravity (Markl, 1962). 



