MINUTE STRUCTURE. 565 



This has a flask-like shape, the cephalic extremity being wide and cup- 

 shaped, the caudal long and tapering. The former is seen to be con- 

 nected with numerous branches of nerve fibres, and corresponds to the 

 nervous layer of the plate just described. 



The columns which compose the four organs of Gymnotus resemble 

 those of the skate in having compartments, each enclosing a pro- 

 toplasmic mass which constitutes the electric plate or disc. This 

 presents the same different layers, though with certain modifications. 

 The nerve fibres enter the caudal aspect of each disc, and appear to end 

 in granular protoplasm containing very conspicuous nuclei ; this caudal 

 surface is thrown into conspicuous folds with secondary villous pro- 

 jections, all of which are richly supplied with nerve fibres. The 

 meandering layer is not conspicuous, being represented by a few fine 

 parallel lines (Pacini), running through the interior of the whole 

 protoplasmic mass, as in the skate organ ; finally, the surface of the 

 cephalic portion is thrown into very prominent papillse, upon which 

 blood vessels ramify. It is evident that the great difference between 

 this organ and that of the skate is the position of the plate layers with 

 regard to the body extremities, the nerved side being caudal in Gymnotus 

 and cephalic in the skate. 



A noteworthy feature is the striking difference which exists between 

 different portions of the whole organ of Gymnotus. The columns near 

 the tail run somewhat obliquely from the ventral towards the dorsal 

 aspect, are yellowish red in colour, and are subdivided into compart- 

 ments of very considerable size, in which the protoplasmic plate occu- 

 pies but a small part of the available space, the clear albuminous 

 substance filling the remainder of the compartment. These columns 

 were supposed by Sachs to be less highly developed; his view is 

 rendered plausible by the microscopic characters of the contained discs, 

 the cephalic surface of each such disc being distinguished by having a 

 large number of long tapering processes, in which may be detected traces 

 of transverse striae with doubly refracting properties, analogous to those 

 of muscle fibres. All the columns receive nerves from the spinal cord ; 

 these emerge from the whole length of the cord, and are the axis cylinder 

 processes of special large cells, the electrical nerve cells. They form a 

 vesicular column on each side, and are seen in any transverse section of 

 the cord to be situated in the grey matter, dorsal and somewhat lateral 

 to the central canal. 1 



The organs of Mormyrus are in many respects analogous to those of Gymnotus, 

 although, owing to the small number of discs and their imperfect development, 

 the total electromotive force of the columns is small. The compartments 

 contain discs athwart the line of the columns, which latter is parallel to the 

 spinal axis. The nerves enter the caudal side of each disc and are derived from 

 special spinal cells like those of Gymnotus. A noteworthy feature is that some 

 fibres decussate and supply the half of the organ which is upon opposite side. The 

 nerve cells also are remarkable since their processes join by short anastomoses. 2 



There are several different varieties of Torpedo, all possessing two 

 electrical organs symmetrically placed on each side of the body. The 



1 For structure of organ in Gymnotus, see Sachs, " Untersuch. am Zitteraal," Leipzig, 

 1881; Pacini, "Sulla struttura intima dell' organo elettrico," Firenze, 1852; Schultz, 

 Arch. f. Anat., Physiol. u. wissensch. Med., 1858, 1862 ; Fritsch, " die elektrischen Fische," 

 Leipzig, 1887. 



a Fritsch, Sitzungsb. d. k. preuss. Akad. d. Wissensch. , Berlin, 1891, Bd. xliv. 



