FUNCTION OF LATERAL-LINE ORGANS IN FISHES. 1S7 



the ampulla' of Lorenzini, they arc undoubtedly closely related to the lateral-line 

 system. They were originally described by Savi (1841) as nervous organs, and a 

 sensory function was claimed for them by Wagner (1847). This opinion was, subse- 

 quently supported by Schultze's discovery (1863, p. 11) that the epithelium of these 

 organs contained an abundance of sense cells. Thus the sensory nature of the vesi- 

 cles of Savi and of the ampulla- of Lorenzini was clearly in the minds of several of 

 the earlier investigators at a time when the nearly related lateral-line system was 

 regarded as a purely secreton mechanism. 



In April, L850, Leydig ( L850a) gave a preliminary account of certain large sense 

 organs found by him in the lateral-line canals on the head of the ruffe ( A<; nna <; rinm). 



and later in the same year he (Leydig, 1850b) figured and described thes gans in 



detail not only in the ruffe, but in several other species of fresh-water lishes. Since 

 he could find no reason to suppose that the slime on the surface of these fishes was pro- 

 duced in the lateral-line canals, and since these canals contained large sense organs, he 

 concluded that the lateral-line system was not a set of elands, but a system of sense 

 organs which he believed to be peculiar to lishes (Leydig, ls.">ob, p. 171). Shortly 

 after this, similar organs were found by Leydig (1851) in certain marine teleosts and 

 bv Midler (1852, p. 149) in elasmobranchs; and a few years later Leydig (1857, p. 

 L96) gave in his text-book of histology, an excellent summary of the liner anatomy of 

 these and other closely related structures. Here he briefly discussed the function of 

 the lateral-line organs, and expressed the belief that if they must be placed under 

 one of the rive sense-, as usually defined, they certainly belonged under touch, but in 

 his opinion they were very probably representatives of a new sense especially adapted 

 for life in the water. 



A few years later Schulze (1861) showed that on the skin of very young fishes 

 there were sense organs essentially like those described by Leydig from the lateral- 

 line canals of mature fishes. These were so distributed as to foreshadow the lateral- 

 line canals, and they undoubtedly represented the organs which were later to occupy 

 these canals. Schulze further demonstrated a similar system of superficial organs in 

 the water-inhabiting stages of amphibians, and thus showed that these organs 

 occurred in other vertebrates than the tishes, ;i conclusion subsequently continued by 

 Leydig (1868), who. though still holding that the lateral-line organs were closely 

 allied to the organs of touch, regarded them as sufficiently distinct to constitute a 

 sixth (lass of sense organs. Leydig also suggested the possibility that these organs 

 might be represented in other groups of the animal kingdom than the fishes and 

 amphibians, and went so far as to intimate that certain glandular structures in the 

 skin of the air-inhabiting vertebrates might have been derived from them. 



In a second paper Schulze (LSTo, p. 83) pointed out the inaccuracy of this opinion 

 and maintained that the lateral-line organs were strictly limited to tishes and the 

 water-inhabiting stages of amphibians. lie also called attention to the important and 

 striking similarity between the sense cells in the lateral-line organs and those in the 

 ear as described by Schultze and by Hasse, a comparison already made by Leydig 

 (1850b, p. lsii). and he concluded that the lateral-line organs were stimulated either 

 bv mass movements of the water, as when a fish swims through this medium or a 

 current impinges on its body, or by water vibrations whose period is longer than that 

 of the vibrations which stimulate the ear. Notwithstanding this supposed relation 



