Phonoreception 499 



by Pumphrey and Rawdon-Smith is less than 5/x. The threshold rises with 

 frequency (Fig. 173). The sensilla seem to operate as pure displacement 

 receptors over the investigated frequency range, and there is no evidence 

 of resonance phenomena. Curve (a) of Fig. 173 is drawn on the assump- 

 tion of a constant displacement of the distal end of the hair of 56 m^. This 

 type of mechanism is probably sensitive to very low frequencies and may 

 also function in determining vibrations in the substrate. 



Other Orthopteran Receptors. Pumphrey and Rawdon-Smith'^^ have 

 also recorded a response from the abdominal segmental nerves of the locust 

 in response to sound, especially when the frequency was about 1400 cycles. 

 The threshold curve indicates sharply tuned resonant structures which 

 Pumphrey and Rawdon-Smith assumed were short stiff sensory hairs. How- 

 ever, no such hairs were found. Melanophis^^ has segmentally arranged 

 scolopidia which may be auditory in function. If their function is auditory, 

 and if these scolopidia occur in Lociista, then they may be the structures the 

 sensitivity of which was studied by Pumphrey and Rawdon-Smith. 



Receptors in Other Arthropods. 



Spiders are sensitive to sound waves in air, and the location of the sense 

 organ is as yet undetermined. However, it seems probable that the hairlike 

 projections on the surfaces of non-insect terrestrial arthropods may serve as 

 acoustic detectors as do those of insects. Furthermore, web-building spiders 

 are capable of very accurate orientation toward a sound that is transmitted 

 through the web or its supports,^ and the logical place to look for the respon- 

 sible receptor seems to be in the hair-like processes. 



It is also known that Mysis " and Palaemonetes are sensitive to sound 

 waves in water and are less sensitive after extirpation of their statocysts. 

 The statocyst, although primarily statoreceptive, apparently has a dual func- 

 tion, as does the sacculus of fishes. 



REFERENCES 



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3. Adrian, E. D., Craik, K. J. W., and Sturdy, R. S., Proc. Roy. Sac. Land., B. 

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4. Barrows, W. M., Biol. Bull. 29:316-332 (1915). Reactions of spider to vibration 

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5. Berger, K., Ztschr. vergl. Physiol. 1:517-540(1924). Sound perception in reptiles. 



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