ON THE ZOOLOGICAL STATION AT NAPLES. 155 



torpedo, on the other hand, the electric organ is somewhat flat and 

 uniform in thickness, and occupies the entire region bounded laterally by 

 the head and branchial sac and the margin of the body, anteriorly by the 

 anterior boundary of the body and posteriorly by the cartilages of the 

 pectoral fins. 



In both forms the organ consists of a large number of pillars or 

 columns, but -while in the torpedo these run vertically and occupy the 

 whole thickness of the organ, and are on the whole of a similar and 

 uniform diameter, in the rays they run lougitudinally, are of variable 

 thickness, and have pointed extremities ; nor do they extend the whole 

 length of the organ, but after a somewhat oblique course they very soon 

 die out. Indeed, the constituent elements of the electrical apparatus of 

 rays are much less regularly disposed than is the case with torpedoes. 

 The walls of the pillar consist of connective tissue, in which the nerves 

 and blood-vessels run, and in torpedoes adjoining columns maybe separated 

 from one another, but this I have not found possible in the rays. 



The columns are found to consist of a large number of superimposed 

 plates, the electric plates, separated from each other by thin transverse 

 partitions of connective tissue, and on one side of these the nerves ramify 

 to a great extent and then terminate. In rays the number of plates is 

 much less numerous than in torpedoes, the individual plates or discs are 

 a great deal smaller in diameter, and of a much greater thickness ; and," 

 further, the ramification of the nerves takes place on the ventral face of 

 the plate in torpedoes, while in rays it is on the anteriorly directed surface. 



In the case of rays I have not been able to find any division of the 

 nerves to supply the plates corresponding to Wagner's bouquet ; they 

 seem rather to branch in the usual way, and distribute themselves along 

 the transverse ])artitions by which the columns are divided. In the 

 torpedo the nerves run from the partition to the ventral surface of the 

 electric plate, and there divide again and again very frequently in a 

 perfectly dichotomous manner ; this ramification takes place pretty nearly 

 in the same plane, so that by simply placing the plate on a slide with its 

 ventral face upwards one is able to make a study of the nerve-branch- 

 ings. In rays, on the other hand, the nerves run backward from the 

 partition immediately in front of the plate, and on their way undergo 

 many divisions, and so reach it in the form of very delicate branches, 

 which run perpendicularly to the surface of the disc. This can only be 

 seen to any advantage in longitudinal or very oblique transverse sections 

 of the organ. Before giving rise to the fine perpendicular twigs the 

 branches of adjoining nerves anastomose, and frequently at the point of 

 union a large nucleus is present. It is not improbable that this ana- 

 stomosis may correspond to the final branching and network in the plates 

 of the torpedo, while the fine delicate twigs may have as their homologues 

 the ' Stabchen ' of Boll. What becomes of the nerve-fibres after they 

 reach the plate I have not been able to make out ; that they give rise to 

 a second reticulation, and by further division become smaller and smaller 

 and gradually pass into the substance of the plate as is stated by Schultze, 

 I have not succeeded in confirming, and consider far from likely, the 

 structure and development of the plate showing its elements to be 

 muscular, and not nervous, as Schultze maintained. 



The disc on which the nerves end consists anteriorly of a finely 

 granular groundwork in which large nuclei are embedded ; then follows 

 a layer of considerable thickness characterised by the presence of 



