no The Life Story of the Fish 



fish there are several canals on each side, and in some the 

 line is broken rather than continuous. 



The purpose of this organ was for long a mystery, and 

 many guesses were made about it, until an American scien- 

 tist settled the question by a simple but ingenious and logical 

 set of experiments. He operated on certain fish, cutting the 

 nerve which connected the lateral line with the brain, and he 

 left intact other fish of the same species. After the operated 

 fish had recovered he put them all through a series of tests 

 to find out what the normal fish could do that the operated 

 fish could not do. He found that they were alike in every 

 way, except that the normal fish would respond to vibrations 

 of low frequency in the water whereas the operated fish 

 would not. Later experiments in England, using an oscillo- 

 graph to measure the electric discharges in the lateral-line 

 nerve, have brought corroborating evidence, and we now 

 know without doubt that at least one function of the lateral 

 line is to receive low-frequency vibrations. 



It is, therefore, very like a hearing organ, with the dif- 

 ference that the vibrations which it receives are of a fre- 

 quency so low that they would reach our ears only as a 

 series of intermittent noises, or more likely would not be 

 heard at all. These vibrations are such as might be caused 

 by the straining of an oar against an oarlock in an angler's 

 boat, or by his footfall as he moves along the bank of a 

 stream. Or, to use a simile more in keeping with the normal 

 life under water, they might be caused by the passing of 

 another fish, or by nearness to an obstacle which would send 

 back through the water the vibrations caused by an approach- 

 ing fish. In the detection of such disturbances the lateral line 

 would serve almost as a long-distance touch organ — a method 

 of touching an object without being actually in contact with 

 it, which might be especially useful in avoiding obstacles in 

 the dark corners of pools and streams, or in finding mates or 



