566 THE PHYSIOLOGY OF ELECTRICAL ORGANS. 



varieties differ, not only as regards adult size, shape, and skin markings, 

 but also in the number of columns which compose each of the electrical 

 organs. Thus in Torpedo occidentalis there are on an average 1069 

 columns, in T. califomica 895, in T. marmorata 450 to 500. 1 



In all varieties the columns are extremely distinct and consist of a 

 series of superimposed compartments, but these are more closely 

 approximated than in the case of the skate or Gymnotus organ, and the 

 electric discs which they contain are proportionately thinner. Since 

 the columns extend from the ventral to the dorsal surface of the organ, 

 and the discs are slung athwart the columns, the surfaces of the discs 

 are ventral and dorsal respectively. The nerves enter to be distributed 

 upon the ventral surface, which presents an extraordinarily beautiful 

 example of the dichotomous division of nerve fibres. This is readily 

 demonstrated in the organ of a young torpedo, after fixation in warm 

 osmic acid. If a single plate is stripped off, and spread out with its 

 ventral surface uppermost, microscopic examination shows innumerable 

 nerve twigs, and it may be seen that the twigs of any one branch do 

 not join those of any other. The nuclei of the primitive sheath of 

 the nerve fibres are conspicuous objects in such a preparation, as also 

 those of the granular protoplasmic mass in which the fibres are situated. 

 In cross-sections of the disc the deeper portions of this multinucleated 

 protoplasmic layer exhibit the ultimate endings of the axis cylinder 

 branches, which, according to Ogneff, are groups of nerve twigs with 

 slight bulbous enlargements, each twig being free, i.e. not connected 

 with its neighbours. A faint fibrillation running across the disc parallel 

 to the surface probably represents the meandering layer of the skate 

 organ, reduced in the torpedo to very small proportions. The dorsal sur- 

 face of the plate is not thrown into folds as in the organs just referred to. 



The nerves which supply each organ spring from prominent eleva- 

 tions, situated upon the dorsal aspect of the medulla. These elevations, 

 one on each side, constitute the electrical lobes of the medulla, and 

 contain a number of large multipolar nerve cells, each of which has one 

 axis cylinder process continuous with an electrical nerve fibre. The total 

 number of such nerve cells (and thus of electrical nerve fibres) in the 

 case of T. marmorata is 58,000 on each side, the fibres being massed 

 for distribution into five nerves, of which the middle are the largest. 

 Each nerve fibre, on entering the connective tissue septa, between the 

 columns of the organ, divides, giving off eighteen branches ; this multiple 

 division of the axis cylinder presents an appearance likened by Wagner 

 to a bouquet. Each of the eighteen branches enters the column at one 

 angle of eighteen successive discs, and as there are six such sets of 

 branches coming from six nerve fibres, and entering the angles of each 

 hexagonal disc, it follows that the nerve cells supply three times their 

 number of discs. 2 The direct enumeration of the discs bears out this 

 numerical relationship, there being about 180,000 discs in an organ of 

 T. marmorata, i.e. 450 columns, with an average of 400 discs in each 

 column. 3 



1 Fritsch, Arch. f. Physiol., Leipzig, 1886, S. 362. 



" Fritsch, Sitzungsb. d. k. prcvss. Akad. d. TFissensch., Berlin, 1889, Bel. Hi. 



3 For structure of organ in Torpedo, there is an extensive literature comprising among 

 others: Wagner, "Ueber den Bau ties elektr. Org. im Zitterrochen," Gottingen, 1847 ; A. 

 Ewald, "Torpedo," Heidelberg, 1880; Schultze, Arch. f. Anat.. Physiol, u. wissensch. 

 Med., 1862; Fritsch, "Die elektrischen Fische," Leipzig, 1887, 1890; Ballowitz, Arch. 

 f. mikr. Anat., Bonn, 1893, Bd, xlii. ; Ogneff', Arch. f. Physiol., Leipzig, 1897. 



