374 



MECHANICAL AND ACOUSTICAL SENSES 



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Figure 28 Whole nerve recordings from left and right spinal nerves of an abdominal seg- 

 ment in a curarized spinal preparation of the dogfish Scyliorhinus. The spontaneous 

 rhythmic discharges had ceased but reappeared in response to strong tactile stimulation 

 on the right side. Time scale— 2 s (Roberts 1969a). 



of the spinal neurons to discharge rhythmically is stabilised by propriocep- 

 tive feedback during movement so that these neurons, which are notable 

 for their extensive dendritic arborizations and, presumably therefore for 

 an extensive synaptic input, are kept from oscillating widly (Roberts 1969d). 



Role of Lateral Line and Labyrinth in 'Hearing' 



Any attempt to relate elements of natural behaviour to specific mechanical 

 stimuli is made difficult in fishes by the presence of the lateral-line system. 

 Were this absent, it could be assumed that the detection of vibrations set up 

 some distance from the fish would be the role of the ear, while the skin 

 tactile endings would respond to water currents and touch; but with the 

 addition of the lateral line, such a simple division is not possible. 



Electrophysiological experiments show that the lateral line is very sensi- 

 tive to water displacements. The recognition of these disturbances when 

 created by nearby moving objects should be useful for the discovery of prey, 

 enemies, and sexual partners. Perhaps it aids in schooling, but whether in 

 fact the lateral line has this role, and just what biological stimuli are detected 

 by the system, have been the subject of much debate and testing. Since 

 Parker's (1905) report that behavioural responses could be triggered by a 

 tuning fork, some workers have maintained that the lateral line is sound- 

 sensitive, whereas others have strongly opposed this view; these opinions are 



