Mechano- and Equilihrium-Reception 523 



eye and head movements are absent in bilaterally labyrinthectomized 

 animals, provided optical stimulation is absent. However, bilaterally labyrin- 

 thectomized dogs can discriminate high angular accelerations, as demon- 

 strated by conditioned reflex methods. '^'^ The sensory cue involved in this 

 discrimination possiblv originates in proprioceptors of the neck muscles. 

 Human beings, subjected to constant deceleration,"*^ give markedly different 

 responses when the whole body is tilted and when only the head is tilted 

 during the deceleration. Those differences in response are attributed to the 

 role of the proprioceptors of the neck muscles. 



It is well established that, after rapid acceleration and deceleration, eye 

 movements persist for about 20-30 seconds. Heyer,^* working with human 

 subjects under constant conditions of acceleration and deceleration, demon- 

 strated that the subjective sensation of rotation persisted significantly longer 

 on acceleration than on deceleration. This difference in duration of sen 

 sation is not understood. It is safe to say, however, that the duration of 

 eye movements and subjective sensation roughly parallels the time course 

 of cupula deflection. 



Orientation in Flying Insects. Statocysts are rare in these animals and, 

 until recently, orientation has been analyzed only in the Nepidae or water 

 bugs. These animals are negatively geotactic, which presumably enables 

 them to reach the surface of the water for breathing purposes. They collect 

 a bubble of air on the under side of their abdomen, which is then utilized 

 during their underwater exploits. Along the lateral edges of the abdomen 

 there is a trough in which are located a series of pits; believed to con- 

 tain sense organs. ^^ These pits are filled with air. In the normal attitude 

 of the bug, the bubble shrinks posteriorly as the air is used. This causes 

 the air-water interface to activate the sense organs and signal the organism 

 to ascend. 



More recently Pringle'^" demonstrated that the halteres are gyroscopic 

 mechanisms which signal any departure from the normal attitude and 

 presumably initiate reflex adjustment. The halteres are found in all groups 

 of Diptera as dumbbell-shaped organs located behind the wings. These 

 halteres are rather complex (Fig. 193), bearing a rich supply of sense 

 organs, a muscle, and a hinge, and are of a shape suited to their func- 

 tion. These halteres oscillate rapidly in a vertical plane during flight at 

 frequencies of 100 to 200 cvcles per second (c.p.s.). Under normal cir- 

 cumstances the wings and halteres are synchronized, but this is not always 

 so. There does, however, seem to be some coupling between the oscillation 

 of the wings and that of the halteres. The oscillation of the haltere begins 

 by mechanical stimulation, i.e., stretching of the muscle. Motor nerve im 

 pulses or electrical stimulation does not produce contractions but merely 

 seems to enhance the excitability of the muscle for mechanical stimulation. '''* 

 That a reflex of some sort is not involved is indicated by: (1) the persistence 

 of this response under conditions of anesthesia which abolish other reflexes, 

 (2) the persistence of this response when the muscle and its nerve is sep- 

 arated from the thoracic ganglion; (3) the persistence of the response when 

 the proprioceptive sense organs (campaniform sensilla) of the wing base 

 are removed; and (4) the lack of sense organs in the haltere muscle and 

 indirect flight muscles. The fact that electrical stimulation elicits no con- 



