vii. 17 



FUNCTION OF LATERAL LINE 



219 



displacements produced by the swimming movements of the fish 

 itself, but this has not been proved. Fishes deprived of the lateral 

 line show no muscular incoordination, although if blind they collide 

 frequently with solid objects. It has often been suggested that these 

 organs serve for hearing, perhaps at low frequencies, but this is 

 probably not so. 



Fig. 136. Responses of a single end organ in a lateral canal of a ray, shown with an 

 oscillograph after amplification. Time signal 10 sec. intervals. The movements of 

 the continuous white line show A, the beginning of a headward flow, increasing the 

 frequency of discharge; B, the end of this flow; c, return of spontaneous discharge 

 after an interval of 28 sec; D, spontaneous discharge 60 sec. later; E, beginning of 

 a tailward perfusion, inhibiting the discharge; F, the end of this perfusion; G, the 

 spontaneous discharge 10 sec. later. (From Sand, Proc. Roy. Soc. B. 123.) 



Study of the electrical activities of these organs in rays has shown 

 that many of them discharge impulses all the time, even when not 

 under the influence of any external stimulation (Fig. 136). By passing 

 currents of water along the tubes Sand showed that a tailward flow 

 checks and a headward flow accelerates this 'spontaneous' discharge of 

 impulses. Such changes in the streams of impulses arriving at the 

 brain could, no doubt, form the basis for initiation of movements of 



