1 86 Papers from the Marine Biological Laboratory at Tortugas. 



electric nerves to pass to the electroplaxes, assuming that they have no 

 peculiarities of interest during their course through the nerve-tracts between 

 the cord and the electric chambers. (The electric chambers are not divided 

 as in Mormyrus by a transverse septum of heavy, opaque, white connective 

 tissue; this can be explained by the fact of their secondary segmentation.) 



As the few fibers destined for any particular electroplax first leave the 

 electric nerve they are directed caudad and are very small in diameter and 

 invested with a fine connective-tissue sheath. This covering is probably 

 medullated in the grown fish. They quickly turn in a gentle curve whose 

 diameter is about half that of the spindle and pass forward through the 

 electric connective tissue to the posterior surface of the electroplax. At the 

 beginning of this curve, or just after leaving the electric nerve, the axis 

 cylinder or neuraxon enlarges to a considerable diameter and becomes very 

 wavy and irregular in diameter. Its course is no longer straight, and it is 

 not possible to find a section of any considerable part of its length, except 

 in some very few cases. Its sheath of connective tissue is loose fitting and 

 the inner side shows a loose reticulum of fine fibrils and plates that form a 

 weak connection between the axon and sheath. 



It is at once apparent in the maze of fibers which approach the electro- 

 plax that the few neuraxones which first entered the compartment are now 

 many in number. Still, it is difficult to see where they branch in the thin 

 sections, owing to their sinuous and irregular courses and to the large 

 numbers of transverse and oblique sections present. In several places this 

 branching was seen, however, and recognized as the same multiple branching 

 which has often been described in the terminal part of nerve-paths and, in 

 particular, in the same comparative region of the electric tissue of Raja by 

 Ballowitz (5) and Retzius (26), in Torpedo by several authors, and especially 

 in Malopterurus by Ballowitz (4), who refers in this article to many other 

 cases. The writer has also seen and figured it in the electric tissue of 

 Astroscopus in a paper soon to appear. In the present case, one section, as 

 can be seen in figure 16, plate 5, exhibits two cases of this branching, one of 

 them showing a single fiber dividing into at least three or four branches; 

 also, figure 25, plate 9, in which there is to be seen a well-defined single fiber 

 dividing into two branches just before they end in two club-shaped nerve- 

 endings in the electric layer of the posterior surface of an electroplax. 

 The abundant nodes of Ranvier, described by Schlichter (30) in the case 

 of Mormyrus, were not observable here, probably on account of the lack of 

 osmic-acid fixation. I have no doubt that they are present and they must 

 be present at the points at which the fibers divide. 



As has already been stated, the fibers now approach and end on the 

 posterior surface of the electroplax, as well as on the lower sides of some of 

 the papillae that arise from it. The mode of ending is not difficult to see, 

 apparently, although this much studied and controverted question should 

 not be approached lightly, especially where the material is merely a subli- 

 mate-acetic fixation stained with iron-haematoxylin and eosin. 



