Z SYDNEY EVANS JOHNSON 



F. E. Schulze carried observation.s a step further and, in 1861, 

 published sketches of histological preparations that embraced 

 bony fishes and gilled amphibia and included in his observa- 

 tions the sense organs of the trunk as well as those of the head. 

 Nevertheless, it was not till the pubUcation of Leydig's elabo- 

 rate paper of 1868 on organs of a sixth sense that the sensory 

 nature of the canal organs was generally recognized. From 

 that time onward the designations sense organs of the lateral 

 line, or of the lateral canal system, came more and more into 

 use. 



Steno's observations, published in 1664 and 1667, were con- 

 fined to pores of the head of a skate (1664) and of a shark (1667). 



Lorenzini, a disciple of Redi, soon thereafter (1678) discov- 

 ered another set of tubular organs on the head of selachians 

 that had been unknown to Steno. These have long been desig- 

 nated the ampullae of Lorenzini. 



Another variety of follicular organs, distributed on the lips 

 and near the mouth of Torpedo, were described and figured in 

 1844 by Savi. 



These three sets of organs have been somewhat confused in 

 discussions of the sense organs of the lateral canal system. 

 Accordingly it is essential to state at the outset that in this 

 paper the ampullae of Lorenzini and the corpuscles of Savi are 

 not taken under consideration. 



As regards the sensory nature of these various organs, Jacob- 

 son, in 1813, maintained on the basis of reasoning that the am- 

 pullae of Lorenzini were sensory organs, probably of a highly 

 elevated sense of touch, and Savi, in the comments on his orig- 

 inal sketches of corpuscles of the torpedo, points out they are 

 provided with more nerves than blood vessels and concludes 

 that the- also are sensory. 



The main question, however, which concerns the canal organs, 

 remained untouched, and it was reserved for Leydig and Schulze 

 to take up the investigation on broader lines. Leydig on the 

 basis of his morphological and histological observations ('50) 

 concluded that the lateral hne organs of the head are sensory 

 in nature and not merely mucous secreting and Schulze ('61 and 



