THE HAKE AND THE SCABBARD FISH 119 



ripples spread away and the ripples fade away as the circles become 

 wider. If two places are touched at the same time two sets of 

 interlacing ripples start out. Each set goes on its own way right 

 through the other set, as if it were not there." A little imagination 

 will make one realise how important these facts are when we en- 

 deavour to understand the function of the organs of the lateral line. 



In a discussion on the significance of the enlarged acoustico- 

 lateralis lobes of Aphanopus carbo there are several interesting 

 facts pointing to a correct interpretation. If we compare the brain 

 of the hake with that of a pollack, both predacious fishes, we note 

 the smallness of the optic lobes in the former (see drawing) ; if sight 

 is of so little importance to the hake in hunting, some other special 

 sense will probably be found to take its place. 



Can the lateral line organs take the place of eyes, and of sight ? 

 Hickling is of opinion that the lateral line organs are direction finders, 

 that is to say, are able to interpret the position of a moving object, 

 producing waves at a distance, as these waves would affect differently 

 a lateral organ situate in the front of the body, from one situate pos- 

 teriorly. Incidentally, it may be noticed that the hake is elongated 

 and, therefore, there is a greater length of lateral line and a longer 

 base for recording waves. This may be expressed in another, more 

 nautical, way, by sa;)^ng the lateral line organs are able to take 

 cross bearings of a distant fish, from which undulations of water 

 replace the vibrations of light or the waves of photons. The func- 

 tion of these organs have recently been investigated by Dr. Sands 

 at Pljanouth ; he has shown that the effect of movements of water 

 in the lateral canals, when recorded by the electric variations in an 

 isolated nerve fibre prove that the lateral line organs are receptors of 

 vibrations. 



These researches by Dr. A. Sand, published in the Proceedings 

 of the Royal Society, have been summarised in the Report of the 

 Council of the Marine Biological Association. His method of investi- 

 gation has shown the great sensitivity of the sense organs to move- 

 ment of fluid in the canal, and has established the exact proportion- 

 ahty between the rate of flow and the frequency of impulse discharge. 

 The behaviour of the sensory system with reference to displacement 

 of fluid in the lateral line canals proves that they record and perceive 

 vibrations coming from a distance ; and the way in which the im- 

 pulse discharges follow the frequency of low tones produced in the 

 neighbourhood of the fish justifies the description of the lateral-line 

 system as a form of auditory organ. We have already shown how 

 the experiments of Bragg prove that waves of low frequency are 

 produced by the movements of a fish, but that they are not of 



