1V>SS BULLETIN OF THE BUREAU OF FISHERIES. 



contained in the air bladder, as conjectured by Richard (1896). In fact, all ray obser- 

 vations supported Bonnier's opinion that Richard's results were due to the severity 



of his operations and not to the loss of the lateral-line organs, and since many fishes 

 with well-developed lateral-line systems have no air bladders, it seems to me highly 

 improbable that these sense organs are directly concerned with the state of the bladder. 



I next repeated Lee's experiments on the toad-fish, Opsarvm tun. and the dog- 

 fish, Mustelus canis. Lee ( 1 Sits. p. llu) states that after the removal of the pectoral 

 and pelvic tins from the toad-fish, the natural means tor support for the resting 

 animal, and the destruction of the lateral line organs, there were '"decided evidences 

 of a lack of the sense of equilibrium." The fishes were unsteady in their movements 

 and would lie quietly upon the side or back, in this respect being in strong contrast 

 with individuals whose tins anil skin had been cut to an equal extent, but whose 

 lateral-line systems were still intact. These, according to Lee. were active and 

 certain in their movements, showed no lack of equilibrium, and in general closely 

 resembled normal individuals. 



My own observations on Opsanus do not support those of Lee. I prepared »i\ 

 toad-fish by cutting off the four tins as Lee did and then severing the nerves to the 

 lateral-line organs. This operation was easily carried out by following the careful 

 topographical account of the lateral-line system given for this species by Clapp 

 (1898). Of the six fishes operated upon one died shortly after the operation but the 

 remaining five all lived over five days and one over a week. These I carefully com- 

 pared with five other fishes from which the four fins had been removed and the skin, 

 but not the nerves to the laterial-line organs, had been cut. So far as the retention 

 of equilibrium was concerned, I found it impossible to distinguish one set from the 

 other. Both, though rather irregular in their locomotion, retained fairly upright 

 positions, and none ever showed the characteristic disturbances seen in the locomo- 

 tion of many fishes from which the ears have been removed. Occasionally individ- 

 uals could be found that would lie quietly often for some time on the side or back, as 

 described by Lee. but these always proved to be moribund and usually died within a 

 day or so after this symptom appeared. Since cases of this kind occurred among 

 those fishes in which the lateral line organs were intact, as well as among those in 

 which the nerves had been cut. I concluded that the loss of equilibrium seen in these 

 instances was not due to the exclusion of the lateral-line system, but to general 

 weakness preceding death. I therefore do not believe, as Lee does, that the loss of 

 the lateral-line organs in Opsanus is accompanied with any special disturbance in 

 equilibrium. 



Lee (189s. p. 112) also experimented upon the dog-fish by exposing the lateral- 

 line nerve and stimulating its central end, whereupon he obtained well coordinated 

 muscular movements like those seen on stimulating the ampullar organs of the internal 

 ear. I have repeated this experiment on Mustelus canis and can confirm Lee's state- 

 ments even to detail. I have worked with care only on the pectoral-fin reactions, 

 but these will suffice to give a clear insight into the nature of the response. When, 

 as Lee states (1898, p. 142), the left lateral-line nerve is stimulated centrally, the left 

 pectoral tin is elevated and the right depressed. Since this reaction, which is always 

 very marked and clear, is of a kind to restore equilibrium, one might conclude with 

 Lee that the lateral-line organs are organs of equilibration, but exactly the same 



