Fl\NCTION OF LATERAL-LINK OBGANS IX FISHES. 201 



is in vibration. In fact the vibration seems to have no effect upon them except in t hat 

 it produces ripples on the top of the water, and when they come under the influence of 

 these they usually descend a few inches into water which, so far as one can judge 

 from the particles of silt contained in it, is not in motion from the surface ripples. 

 Here they will remain and sport about during the vibrations, though this region 

 would be immediately deserted by a normal fish. Hence I conclude that a body of 

 water vibrating at a relatively slow rate, six per second, is a stimulus for the lateral 

 line organs in Wund/ultts heteroclitus. 



The reactions of Fundulus majalis to vibrations of low frequency, except for 

 the darting movements already mentioned, were almost identical with those of K 

 h, tt roclitus. Normal individuals reacted to the vibrations usually at once by descend- 

 ing; cut ones gave no evidence of being stimulated. In one set of the normal fishes 

 that were being tested preparatory to operations two were found that could not be 

 said to respond to the vibrations. Such conditions were never met with in F. het- 

 erocUtus, and they were so rare in F. m<ij<ilis that they constitute an unimportant 

 exception to the statement that the two species in their lateral-line reactions are 

 essentially alike. 



Stenotomus chrysops when put in the aquarium usually swam down to the bot- 

 tom and remained in the deeper water, sometimes with the lower fins in contact with 

 the floor of the aquarium, sometimes a few inches above this. In all tests of vibra- 

 tions made with these fishes, care was taken that the stimulus should be applied only 

 when the fishes were not in contact with any solid bod} 7 , i. e., when they were sus- 

 pended somewhat above the bottom of the aquarium. Under such circumstances a 

 noiseless vibration almost invariably called forth a very characteristic reaction. 

 When quietly suspended in the water the fish usually rests with its head pointed 

 obliquely downward and its tail up. On stimulating it with a vibration it almost 

 invariably sets its fins and changes the direction of its axis so that its head points 

 obliquely upward. This was observed clearly in six out of seven normal fishes. 

 These six were then operated upon by cutting the nerves to the lateral-line organs. 

 Five recovered, and none of these reacted to the vibrations of low frequency unless 

 the aquarium was made to vibrate very considerably. Under such circumstances 

 occasional, but unquestionable, reactions, precisely like those just described, were 

 observed. Since these reactions are not interfered with by cutting the eighth 

 nerves, and occur w r hen the literal-line organs are excluded, it is probable that they 

 result from a stimulation of the general cutaneous nerves. Thus in Stenotomus 

 chrysops one form of stimulus is probably effective for two sets of sense organs, 

 those of the skin and those of the lateral-line system. 



In testing the smooth dog-fish, MusteVm canis, for reactions to vibrations of low 

 frequency. I found the ordinary individuals too large for work in the aquarium, and 

 I therefore experimented on young animals not over a foot and a half in length. As 

 already noted, none of the specimens 1 tested gave any response to the tuning fork 

 at 100 vibrations per second. To the slower vibrations, six per second, all fishes 

 tested w r ere very responsive and reacted usually in a very uniform way. In seven young 

 fishes that were tested all raised the tail when the aquarium was made to vibrate, and 

 if the fishes were high in the water they usually swam to the deeper situations. 

 These reactions, particularly the elevation of the tail, were unusually regular. 1 



