144 American Fisheries Society 



they were in water not disturbed by the ripples. They 

 doubtless became aware of the ripples through their ac- 

 tion on the nerve endings in the skin. It was found that 

 the rocking of the aquarium produced vibrations, i.e., 

 back and forth movements of the water — at the rate of 

 about six per second. It is these vibrations, too slow to 

 affect the ear, to which the lateral line organs are sensi- 

 tive. The movements of the water doubtless reach the 

 lateral line organs through the pores in the skin. 



Parker found that normal killifish descended to the 

 bottom of the aquarium when strong ripples were pro- 

 duced by blowing on the surface of the water. Fish with 

 cut lateral-line nerves did not go to the bottom when rip- 

 ples were produced. They merely kept out of the agi- 

 tated water very near the surface. He adds : "There is 

 no doubt in my mind that when wind blows on the sur- 

 face of the water it causes a motion of the deeper water 

 which stimulates the lateral line organs." In this way 

 fish are made aware of wave action before they reach the 

 agitated surface and may avoid it by descending. 



When a stone was dropped into an aquarium contain- 

 ing normal killifish in such a way that they could not 

 see it, the fish responded by springing away from the 

 center of disturbance. Fish with cut lateral-line nerves 

 did not respond. Parker concludes that "disturbances 

 produced by such an object as a stone falling into the 

 water stimulate the lateral-line organs with more or less 

 directive effect." The disturbances produced by jumping 

 frogs or leaping fish may thus be detected and located 

 at night. The caster's bait or possibly even the gently- 

 falling fly may be located by their impact on the water, 

 when it is not possible for the fish to see them. The fish 

 then possesses a capacity not present in land animals and 

 obviously of great use to it. 



Parker (1910b), has also studied the lateral line or- 

 gans of the salt water dogfish (Mustelus) . In this form 

 he found that pressure on the lateral line caused the 

 breathing to be slowed or stopped, even when the skin 

 itself had been made insensitive to pressure as well as 



