L88 BULLETIN OF THE BUKEAU OF FISHERIES. 



to the ear. Schulze agreed with Leydig in regarding the lateral-line organs as organs 

 of touch, though specially modified to meet' the requirements of an organism living 

 in the water. 



About ten years after the appearance of Schulze's second paper, Dercurn (1880, 

 ]). 154) called attention to the fact thai in many fishes the lateral-line canals were 

 almost if not entirely closed, and that in consequence water could not flow through 

 them, as was supposed by Schulze. Dercum, however, pointed out that since many 

 of the canals were separated from the outer water by only a layer of thin skin applied 

 to the membrane of the canal wall, the system might be said to possess numerous 

 drumheads through which vibrations in the surrounding water could be transmitted 

 to the fluid within the canal, and thus these vibrations could become effective in 

 stimulating the lateral-line organs. Dercum also suggested that the effect of the 

 vibrations might be the more intense the more nearly perpendicular they were to 

 the surface of the canal on which they fell, and in this way it was conceivable that a 

 tish might orient itself in reference to the direction of the vibrations. 



These views were in large part accepted by Emery (1880, p. 48), who emphasized 

 the comparison between the lateral-line organs and the internal ear. and thus lead 

 to the opinion subsequently expressed by Mayser (1881, p. :-111), Bodenstein (1882, 

 p. 137), and P. and F. Sarasin (1887-1890, p. 54). that the lateral-line organs were 

 •accessory ears. 



Meanwhile Merkel (1880, |>. 55). without knowledge of the contributions made 

 by Dercum and by Emery, showed that it was unlikely that water could be said ever 

 to stream through the canals, and yet he gave very good reasons for supposing- that 

 the lateral-line organs were adapted to a mechanical stimulus. From his standpoint 

 there was insufficient ground to consider the lateral-line organs as constituting a sixth 

 group of sense organs, and he was convinced that the\ were merely tactile organ- 

 somewhat modified for aquatic life. 



The opinions thus far presented as to the function- of the lateral-line organs are 

 in no instance based upon experimentation, but upon such indirect evidence as that 

 afforded by the structure of the sense organs and of their surrounding parts. 



Previous to the appearance of Fuchs's paper in 1894 very few investigators had 

 made experiments on the lateral-line organs, and such experiments as had been 

 undertaken were of a very simple and tentative character. The earliest of these 

 was the work of Bugnion (1873, p. 302), who showed that a living Prott us was not 

 especially sensitive to solutions of alum, salt, or weak acid applied to the lateral- 

 line organs, but that it reacted vigorously when these organs were touched with a 

 needle. Later de Sede (1884, p. 469) reported that fishes in which the lateral line 

 had been cut were less successful in guiding themselves in an aquarium containing 

 numerous obstacles than were normal fish, and he stated that in his opinion the 

 lateral-line organs did not represent a sixth sense but were organs of touch especially 

 concerned with directing the animals. Bateson, some years later (1890, p. 237), 

 stated that he had been unable to get responses from fishes when food substances 

 were tried as stimuli for the lateral-line organs, and lastly, Nagel (ls'.>4, p. 191) 

 found no evidence that the lateral-line organs of fishes and amphibians were stimu- 

 lated chemically: when the lateral-line nerves in Barbus JluviatiUs were cut on both 

 sides the fish apparently remained normal, but when in certain fish (Scbuppfisch) 





