38 THE PHYSIOLOGY OF INSECT SENSES 



plate (Mittelstaedt, 1952) (Fig. 27). The role of these sensory systems 

 was demonstrated by the following series of experiments. If the inner- 

 vation from all hair plates is cut so that no information is forthcoming 

 from these organs the accuracy of hitting drops to 20-30 per cent. 

 With deafferentation of the left side only, missing increases, and there 

 is a tendency to strike to the right. In other words, proprioceptive 

 information coming only from the right misleads the animal into 

 believing that its head is turned to the right whereas it is not. If the 

 head is held in a fixed position relative to the prothorax by a balsa- 



FiG. 28. Ventral view of the campaniform sensilla in the trochanteral region 

 of the third right leg of Pe rip lane ta. C, coxo-trochanteral condyle; 

 E, extensor trochanteris and its accessory apodemes ; F, flexor troch- 

 anteris; H, trochantero-femoral hinge joint; 2, 3, 4, groups of campani- 

 form sensilla. (Redrawn from Pringle, 1938c.) 



wood bridge so that the neck region is not touched accuracy of hitting 

 decreases to 25 per cent if the head deviates from the body axis by 

 10-30 degrees. The prey is missed to the left if the head has been turned 

 to the right, and vice versa. 



If head fastening and unilateral extirpation of proprioceptors are 

 combined the effects of both are superimposed, the loss of one-half of 

 the neck receptors being equivalent to a deviation of the head of less 

 than 20 degrees. If the free head is loaded with an extraneous force 

 performance remains normal until the load surpasses twice the head 

 weight at twice its diameter. In short, direction of stroke depends on 

 feedback processes which control the position of the head. Fixation 

 movements of the head are steered by the difference between the 

 optic-centre message (a function of the angle between prey and 



