1 Mi BULLETIN OF THE BUREAU OF FISHERIES. 



and their environment withal is so different that they afford a most fascinating tield 

 for investigation. It is now fairly well established that many .fishes possess in a 

 high functional state the five chief senses of man taste, smell, touch, hearing, and 

 sight; but it is also known that many fishes possess a sixth set of organs, the 

 lateral line organs, for which there is no representative in man. As these are well- 

 developed and conspicuous structures in many ease.-, they may be suspected of 

 playing an important part in the economy of these animals, and it is the purpose of 

 this investigation to ascertain something of their role in the ordinary habits of some 

 of our fishes. 



HISTORICAL REVIEW. 



Every one who is at all conversant with the external markings of fishes is 

 familiar with a line which, in most instances, extends along the side from tail to head. 

 This line, known from its position as the lateral Hue. consists usually of a row of 

 small pores which lead into an underlying canal, the lateral-line canal. In the head 

 of the fish this canal usually branches into three main stems, one of which passes 

 forward and above the eye. another forward and immediately below the eye. and a 

 third downward and over the lower jaw. These three canals, like the lateral-line 

 canal, open on the surface by numerous pores, and, together with this canal, constitute 

 the lateral-line system. 



According to Leydig ( 1868, p. 3) the pores of these canals were recognized over 

 two centuries ago by Stenon (1664) and by Lorenzini (1678) in elasmobranchs, and 

 by Rivinus (1687) in fresh-water fishes. Subsequently the canals were described b\ 

 many of the earlier anatomists, particularly by Monro (l~s">). and an excellent sum- 

 marized account of them was given by Stannius (1846, [>. 49) in his comparative 

 anatomy of the vertebrates. Thus before the middle of the last century the gross 

 anatomy of these organs had come to be fairly well recognized. 



All the earlier investigators, so far as their opinions are known to me, seem to 

 have regarded the lateral-line system as a system of glands for the production of the 

 mucus so characteristic of the skins of many fishes. Suggestions contrary to this, 

 however, came from two sources. First, observations on elasmobranchs had shown 

 that this group possesses, in addition to the lateral-line system proper, a set of closely 

 related organs, the ampullae of Lorenzini. Jacobson (1813) studied the structures of 

 these organs with the view of determining what their probable function was. and 

 concluded from their extensive nerve supply that they were certainly sense organs 

 and probably stimulated mechanically, like delicate organs of touch. Treviranus 

 (1820, p. 146), concurred in Jacobson's opinion that the ampullse were sense organs, 

 and believed that they probably represented a sense cpiite distinct from any that we 

 possess. Knox (1825, p. 15) in reviewing the whole subject made the interesting 

 statement that "we can not * * greatly err in considering these organs as 



organs of touch, so modified, however, as to hold an intermediate place between the 

 sensations of touch and hearing." Finally, Savi (1841) suggested that in the torpedo 

 they might be organs for the reception of electrical stimuli. 



A second body of evidence that suggested the nonsecrctory nature of the lateral- 

 line system came from investigations on the vesicles of Savi. These are closed, sac- 

 like organs found in clusters in the anterior part of the head of the torpedo. Like 



