PERIPHERIC TERMINAL ORGANS OF THE NERVES. 171 



taken from the Mormyrus, shows the electrical plates forming 

 direct expansions of the nerve-fibre substance, from which it 

 appears that the nerve fibres penetrate foramina in the plates 

 (as in some species of Mormyrus and Malapterurus) before they 

 break up in its substance. 



The point of entrance always occurs on one only of the 

 two surfaces of the disk, and, indeed, on the same or corre- 

 sponding surface of all the plates of the same animal; thus, for 

 example, in the torpedo, in which the plates have a dorsal and 

 ventral surface, the nerves are always applied to the ventral 

 surface, the dorsal remaining smooth ; consequently all these 

 electric plates have a smooth free, and a rough surface to 

 which the nerve fibres are attached, and these all look in the 

 same direction. At the moment of the discharge in all the 

 electric fishes hitherto examined, that side of the animal to 

 which the rough surfaces of the electrical plates are turned is 

 negative as compared with the opposite. In Malapterurus 

 only a single primitive nerve fibre, which has just previously 

 lost its medullary sheath, penetrates each plate ; but in all 

 other animals many fibres enter. The structure of these 

 electric plates, composed of albuminous material, differs in two 

 points from the former. The plates of the true electric organs 

 are homogeneous disks, slightly uneven on their free surface, in 

 the interior of which oval or spherical nuclei, surrounded here 

 and there with a little finely granular substance, lie scattered 

 at definite distances. The plates of the so-called pseudo-electric 

 organs, on the other hand, exhibit similar nuclei, but their sub- 

 stance is not homogeneous, being marked by delicate, meandering, 

 and looped systems of lines, which result from their complicated 

 structure, composed of a number of layers of very thin curved 

 plates. The tissue in some measure calls to mind that of the 

 transversely striated muscles * 



* A. Ecker, Untersuchungen zur Ichthyologie, Freiburg, 1857; Berichte 

 der Naturf. Gesellschaft zu Freiburg, 1858, No. 28. Max Schultze, Uber 

 Pseitdo-clectrik. Organ, Sitzungsberichte der Naturf. Gesellschaft in Halle, 

 1857, p. 17 ; and in Muller's Archiv, 1858, p. 193. Also Bilharz, Das Elektrik. 

 Organ des Zitterwelses, 1857 ; and Max Schultze, Zur Kenntniss der Elek- 

 trik. Organ der Fische, 2 Abtheilungen. Halle, 1858 and 1859. 



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