FUNCTION OF LATERAL-LINE ORGANS IN FISHES. H»7 



Similar experiments were made with Funckdw majalis and Steitotomus chrysops, 

 both of which gave results identical with those obtained from Fhtndulus heteroelitus. 

 Pseudopleuronectes america/nus, normal and cut, also swims against the current, l>ut 

 often takes hold of the bottom of the trough by a sucker-like action of the whole 

 body. This temporary anchoring, however, was as characteristic of the cut fishes as 

 it was of the normal ones, and there is no reason to suppose that the lateral-line 

 organs were involved. 



The larger fishes. Mush lus r,m is and Iiujn < rinact </. were tested not in the trough 

 but at one of the tide openings on the wharf outside the laboratory. Here at certain 

 tides a steady broad current maintains itself, and in this it was comparatively easy to 

 experiment with these fishes. Normal and cut individuals were put into a simple har- 

 ness made of twine and to which a cord was attached so that they could be conven- 

 iently restrained. By this means they could be placed in the current where desired 

 and their reactions noted. Both the dog-fishes and the skates swam vigorously 

 against the current, and this happened irrespective of the condition of the lateral 

 line. In fact it was impossible to tell from the reactions of the fish in the water 

 whether the nerves to the lateral-line organs had been cut or not. My own experi- 

 ments, therefore, confirm the opinion of Tullberg (1903, pp. 13, 15) that the lateral- 

 line organs are not concerned with swimming against a current. 



Stimulus tn equilibrium. — The ability of a fish to keep its equilibrium at rest or 

 in motion has, from time to time, been stated to be dependent at least in part on the 

 lateral-line organs. So far as I am aware, the first investigator to make suggestions 

 in this direction was Richard (1896, p. 131), who supposed that the lateral-line organs 

 were at least indirectly connected with the equilibrium of a fish in that they influenced 

 the amount of gas in the air bladder. Lee (1898, p. Ill), however, first clearly 

 expressed the belief, based upon extended observations on the toad-fish and the dog- 

 fish, that the lateral-line organs were primarily organs of equilibration. Because of the 

 growing favor in which this view has been held, I felt that it was desirable not only 

 to make new observations in this direction, but also to repeat carefully the experi- 

 ments of those who had already advocated this theory, with the view of gaining a 

 critical insight into the present standing of the question. For these reasons 1 have 

 carried out experiments on the equilibration function of the lateral-line organs in 

 /■'inn! 'a! 'us heteroelitus, Stenotorrms chrysops, Opsanus Uni. and Must, I us cants. 



When the nerves to the lateral-line organs in the species of fishes just mentioned 

 were cut by the methods already described, and the fishes were allowed to recover 

 from the shock of the operation, itrwas remarkable how little changed they seemed to be. 

 So far as their ordinary movements were concerned they were often indistinguishable 

 from normal fishes. They swam with agility and kept their equilibrium. perfectly. 

 .My own observations entirely support Lee's statement (1898, p. 110) that the destruc- 

 tion of all the lateral-line organs "does not seem to interfere much, if an}', with the 

 animal's equilibrium.'' I usually found it impossible to bring a cut fish to rest on its 

 side or back, for when displaced from its usual upright position it reacted as a normal 

 fish by struggling to return to that position. 



Those fishes that possess air bladders, such as Fundulus and Stenoto?nus, had 

 no difficulty after the operation in keeping below the surface, and I found no reason 

 to suppose that the lateral-line organs had any influence on the amount of gas 



