136 BRAIN AND BODY OF FISH 



It must be remembered that the lateral Line of the black scabbard 

 fish may extend for from four to five feet or more and, therefore, a 

 vibration reaching the fish when in an obhque position as regards 

 the object, from wliich the chsturbance proceeds, would excite the 

 anterior sense organs with a vibration of greater amplitude than 

 that wliich would reach the organs situated at the posterior extremity. 

 This, it is clear, would enable the lateral line to be used as a direction 

 finder. When the fish becomes directly head on to the object pro- 

 ducing the waves, the lateral organs of either side would receive an 

 equal stimulation. The fish would now go all out in the direction 

 of equal stimulation and on sighting the prey, when almost on top 

 of it, would open its capacious mouth, and the final stage of the 

 tragedy would end in the capture and swallowing of the victim. 

 It is difficult to conceive any other system of direction fincUng than 

 a series of observation points situated along a base of several feet, 

 and the proved capabihty of the lateral fine organs to receive such 

 vibrations, as would be made by a moving object, makes this 

 explanation seem most probable. 



When we add to these considerations the facts of the great 

 enlargement of the acoustic tubercles in those bathysmal fishes, 

 which can find no use for sight in hunting for their daily bread, and 

 also recall the fact that the eyes of these fish, though large, are 

 associated with quite smaU optic lobes, there seems no doubt 

 that this explanation of their methods of hunting is liighly 

 probable. 



We have mentioned the more recent work on the function of 

 the lateral-line organs, but have not described the work of G. H. 

 Parker, who cut the nerves of the lateral line and also the fifth and 

 seventh nerves supplying the similar organs on the head of fish ; he 

 then compared the behaviour of fishes so treated with normal 

 specimens. The result of these experiments was to suggest that the 

 chief use of the lateral-line organs is to perceive the movements of 

 other fish in the water. 



Cumiingham, in commenting on Parker's work, says, " we do not 

 know at present to what distance vibrations due to such movements 

 would extend, but it is evident that if a fish is affected by a body 

 falhng in the water, it must also perceive the movement of another 

 fish or animal in the water. The above account of the various 

 methods of hunting that are employed by fishes has proved that some 

 fish hunt by sight, some by smell, and some by taste, but experiments 

 have so far not been made to ascertain ho w^ far a fish A\ithout sight 

 or hearing would be able to preceive an enemy in its neighbourhood 

 or detect the exact position of the fish it preys upon. 



