202 BULLETIN OF THE BUREAU OF FISHERIES. 



noticed no change in the respiratory rate. It was with difficulty that even these 

 young' fishes were tested, for, since they were relatively large, it was only now and 

 then that they were not in contact with solid parts of the acquarium, and consequent!}' 

 in position for satisfactory stimulation. Notwithstanding this difficult}', however, 

 enough unquestionable reactions were obtained to place beyond doubt the statements 

 made above. 



After the nerves to the lateral-line organs were cut, both the elevation of the 

 tail and the downward swimming ceased. To ascertain how much of the loss of 

 response was due to the cutting of the skin, etc., I made the necessary skin apertures 

 for cutting the nerves in one individual, but did not sever the nerves, and then tested 

 the animal. It still elevated the tail with great regularity on stimulation. On cut- 

 ting the nerves this reaction entirely disappeared. Hence 1 believe the loss of react- 

 iveness is due to the elimination of the lateral line organs and not to the shock of the 

 operation. Six of the seven dog-fishes operated upon recovered, and most of them 

 lived for two or three weeks after the operations. When tested toward the end of 

 this period they were as characteristic as they were a short time after recovery. 



1 attempted similar experiments with small skates, Iinjn , riiuica. and succeeded 

 in getting on stimulation excellent tail reactions, like those described for the dog-fish, 

 but since these fishes were always in contact with the solid bottom of the aquarium 

 it was impossible to say with certainty that they were not directly stimulated through 

 their tactile organs. On cutting the nerves to the lateral-line organs, however, these 

 tail reactions disappeared. Although I believe it would be hazardous to draw any 

 conclusion from the experiments on the skate just recorded, the records on the four 

 other species of fishes tested show beyond a doubt that the lateral-line organs are 

 stimulated by water vibrations at the rate of 6 per second, though they are not stim- 

 ulated when the rate reaches 100 per second. 



DISCUSSION OF KESULTS. 



From the foregoing experiments 1 conclude that the lateral-line organs of the 

 species of fishes experimented upon are not stimulated by light, heat, salinity of 

 water, food, oxygen, carbon dioxide, foulness of water, pressure of water, currents, 

 and sounds. They are stimulated by vibrations of low frequency, as surmised by 

 Schulze (1870), and these may be of service to the fishes in their orientation and 

 equilibration reflexes, as suggested by de Sede (188i), Bonnier (1896), and especially 

 by Lee (1898). There is, however, no reason so far as I can discover, for designat- 

 ing these organs as special organs of equilibration such as the ear. for in this respect 

 they are of no higher value than the skin, and they are certainly inferior to the e\ e. 



The stimulus for the lateral-line organs (a water vibration of low frequency) is 

 a physical stimulus intermediate in character between that effective for the skin 

 (deforming pressure of solids, currents, etc.) and that for the ear (vibrations of high 

 frequency), and indicates that these organs hold an intermediate place between the 

 two sets of sense organs named. This opinion, even from an actual genetic stand- 

 point, has already been urged by many observers. Leydig (1S501), p. 180) long ago 

 pointed out the histological similarity between the sense organs of the internal ear 

 and those of the lateral-line system; and Schulze (l87i») emphasized this relation and 



