GENERAL STIMULATORY ORGANS 153 



sound perception. This conclusion is in accordance with their 

 gross and minute structure and is also supported by analogy with 

 the better-known organs, of a somewhat similar nature, found in 

 the Acridiidic. Certain experiments carried out by Eggers afford 

 further support to this belief. This observer states that when the 

 tympana of both organs are destroyed, the moths so treated no 

 longer react to tests with sounds. When, however, a single 

 tympanum is destroyed, the insects responded to sound stimuli, 

 in more than half the cases tested, by flying. With both organs 

 left intact reaction to different sounds was expressed either by 

 flying or by elevating and moving the wings. Amputation of the 

 antennae did not interfere with response to sounds, while insects 

 whose wings had been cut off still responded, either by running 

 or by movements of the antennae or legs. The most puzzling 

 feature is the real significance of sound receptors in an order where 

 sound production appears to be confined to relatively few species. 

 In some cases, e.g., Vanessa butterflies, a faculty for sound pro- 

 duction prevails and yet tympanal organs are wanting. It is 

 possible that sound vibrations — inaudible to human senses in 

 many cases — may be produced by Lepidoptera and be perceived 

 by the organs in question. In this way individuals may perhaps 

 become aware of the proximity of other members of their species, 

 but it has to be admitted, however, that the suggestion is merely 

 hypothetical. 



6. General Stimulatory Organs 



Stimulatory organs are sensory organs whose functions are to 

 send continuous afferent stimuli to the central nervous system. 

 These stimuli, it is claimed, are essential to the normal and proper 

 working of the nerve-muscle system or of certain reflex arcs. 

 They are necessary for the production and maintenance of muscle 

 tonus and to increase the kinetic efficiency or the contractility 

 of the muscles. Most sensory organs, in addition to their normal 

 specific receptor ability, also probably exercise stimulatory 

 functions in keeping the nervous system in a reactive condition 

 [vide Wolsky, 1933). 



In the modern interpretation the dorsal ocelli of adult insects 



