368 



1 ^^JjK^j\M^A^^. 



3»- 



j^J/Ak. 



*^ m^'w 'I 



4 »----^UA/VokK^M 



40m 



MECHANICAL AND ACOUSTICAL SENSES 



B 



- frwtt^ 



n^J^tjt^^^^ 



sec 



40 msec 



Figure 24 Total lateral-line nerve activity in response to head lateral-line stimulation of 

 dogfish (Scyliorhinus). Traces Al, A4, Bl, and B3 were recorded when the fish was sta- 

 tionary. A2 and B2 were recorded during violent movement and A3 during slow, steady 

 swimming. All traces in B were taken after the nerve had been cut centrally to eliminate 

 any efferent nerve impact (Russell and Roberts 1974). 



SPINAL CORD 



MOVEMENT ON 



MOVEMENT 



EFFERENT CELLS 



LATERAL-LINE 



Figure 25 Schematic showing how the movement centres of the hindbrain 

 and efferent neurons discharge concurrently and bring about an inhibition of 

 the lateral-line hair cells during body movement. 



A direct test of this theory remains to be performed, although it should 

 not be difficult to see whether lateral-line organs are protected by the ef- 

 ferent fibres. Certainly, strong stimulation has a powerful action on lateral- 

 line activity, for, as is shown in Figure 26 for a single unit lacking an 

 efferent supply, strong mechanical stimulation is followed first by complete 



