190 BULLETIN OF THE BUREAU OF FISHERIES. 



lateral-line organs were intact, showed no lack of equilibrium, and in its general 

 behavior closely resembled a normal tish. Moreover, Lee found that the stimulation 

 of the central end of the lateral-line nerve of a dog-fish resulted in perfectly coordi- 

 nated tin movements, and he therefore concluded that the organs of the lateral line 

 are equilibration organs. How these are stimulated Lee did not attempt to decide. 

 though he suggested ( 1898, p. 143) that pressure changes in the. surrounding medium 

 may be the means of stimulation. 



Five years later, in experimenting on the sense of hearing in fishes, 1 made some 

 observations on the lateral-line organs of Fundulus (Parker, 1903a, p. 59; 1903b, 

 p. 197). These led to the conclusion that the lateral-line organs in this tish were 

 stimulated by a very slight mass movement of the water, and they have afforded the 

 point of departure for the present investigation. 



In summarizing this historical review, it is clear that no one has ever brought 

 forward the least reason to suspect that the lateral-line organs are ever normally 

 stimulated by light, heat, or other ether disturbances. It is also very improbable 

 that they are stimulated chemically, for in many instance- the covered situation of 

 the organs is not favorable for this form of stimulation, and the direct experiments 

 of Bugnion (1873) on Prott us, of Bateson (1890), and of Nagel (1891) on several kinds 

 of tish. and of Fuchs (1894) on Torpedo and Raja have always given negative results. 

 On the other hand, it i- almost universally admitted that the normal stimulus for 

 these organs must be of a mechanical kind, either simple contact, as in touch, or 

 vibratory contact, somewhat as in hearing. It is on this point that the majority of 

 investigations disagree, some maintaining that the lateral-line organs are simply 

 organs of touch (Merkel, de Sede), or of pressure (Fuchs). others that they are organs 

 belonging to an independent class, probably intermediate between touch and hear- 

 ing (Leydig. Sehulze, Dercum, Parker), and. lastly, those that believe them to be 

 accessory auditory organs (Emery, Mayser, Bodenstein, P. and F. Sarasin). That the 

 lateral-line organs were necessary to successful locomotion as organs of equilibration, 

 etc.. was first suggested, I believe, by de Sede; and this opinion has received the sup- 

 port of Nagel, Bonnier, and especially of Lee. In attempting to decide between 

 these various views, the first question that arises is: What is the normal stimulus 

 for the lateral-line organs? It is the object of this investigation to find an answer 

 to this question. 



MATERIALS AND METHODS. 



The experiments about to be described were carried out chiefly on the common 

 mummichog, Fundulus heteroclitus, a tish of convenient size, great hardiness, and 

 everywhere abundant in the neighborhood of the biological laboratory of the United 

 States Bureau of Fisheries at Woods Hole. Mass.. where the experiments were made. 

 Besides this species seven others were also tested, though not with a full range of 

 stimuli. These additional species were the smooth dog-fish, Mustelus canis; the com- 

 mon skate. Raja erinacea; the killi-fish, Fundulus majalis; the scup, Stenotomus 

 chrysops; the toad-fish, Opsanustau; the common flat-fish, Pseudopleuronectes ameri- 

 canus; and the swell-fish, Ohylomycterus sckwpfi. 



The general method of experimenting was to cut the nerves connected with the 

 lateral-line organs of a number of individuals of a given species, and. after the tish 



