196 BULLETIN OF THE BUREAU OB' FISHERIES. 



These, observations make it appear improbable that changes in hydrostatic pres- 

 sure, as suggested by Fuchs (1894, p. 474), are stimuli for the lateral-lino organs. 

 Nor in fact do the observations made by Fuchs really lend much support to this 

 hypothesis. He found that when he pressed on the lateral-line organs of Baja, the 

 electrical ehanges in the nerves connected with them indicated that the organs had 

 been stimulated. But the pressure thus exerted was without doubt of a very different 

 kind from increased or decreased hydrostatic pressure; it was very probably a 

 il, forming pressure and not one that exerts its influence in all directions equally. It 

 is well known that for the stimulations of the tactile organs of the human skin a 

 deforming pressure is vastly more effective than such a pressure as is obtained by 

 putting the hand deep in water. Under such circumstances the tactile sensations are 

 not strongest from the parts under greatest pressure but from the region of greatest 

 deformation, i. e., where water and air meet. It seems to me, therefore, that Fuchs's 

 experiments demonstrate that the lateral-line organs can be stimulated by a deforming 

 mechanical influence, but since hydrostatic pressure does not deform to any great 

 extent, there is no reason to suppose that it stimulates these organs. Hence I do not 

 think that my observations are at variance with those of Fuchs, but that he drew a 

 wrong inference from what he observed. 



Currents. — From the time of Schulze's second paper on the lateral-line organs 

 (1870), water currents have been regarded with more or less favor as stimuli for the 

 lateral-line organs. To ascertain whether currents do stimulate these organs, I have 

 experimented on Fundulus heteroclitus, F. majalis, Stenotomus chrysops, Pseudqpleu- 

 ronectes americanus, Must, I us cams, and U«jn i-rlnacea. All these fishes when intro- 

 duced into running water swim against the current, i. e., they are strongly rheotropie. 

 I tested the smaller species (Fund/this heteroclitus, F. majalis, Stenotomus 

 chrysops, and Pseudopleuronectes americanus) by exposing them in a large open 

 trough to a gentle flow of water. The trough, which was about 50 cm. wide, always 

 contained a depth of at least 10 cm. of water and was about 3 meters in length. An 

 inlet was established at one end and an outlet at the other, and a gentle current of 

 water was kept flowing through the trough. A normal Fundulus heteroclitus when 

 put in this trough immediately turned its head against the current and swam toward 

 tlie source, often making its way actually into the open end of the inlet tube. If in 

 its progress the fish was swept into the adjacent and more quiet water near the side 

 of the trough, it would often sport about there for a while, but on returning to the 

 current it woidd take up again its course toward the inlet. At times when the 

 current was strong there would form on the sides of the trough small backset 

 currents, and it was instructive to observe how quickly the fish reversed its direction 

 when by any accident it was carried from the main current into a backset. In all the 

 many tishes tested, irrespective of illumination, etc., they swam against the current. 



Individuals in which the nerve- to the lateral-line organs had been cut proved 

 to be absolutely indistinguishable from normal tishes under these conditions. In 

 agility and certainty of response there was no difference between the two set-. 

 Hence I was led to conclude that the lateral-line organs were not essential to the fish 

 in swimming against a current, and that therefore a current was probably not a 

 stimulus for these organs. 



