214 LECTURE Vlll. 



placed. Hunter counted about 240 of these plates in a single inch 

 of length of the hoi-izontal membrane. He rightly compares those 

 stronger membranes to the aponeurotic walls of the prisms of the 

 Torpedo, and the intersecting delicate plates, to the partitions of the 

 prisms : a pellucid liquid intervenes between the plates of the Gym- 

 notus ; and, if we admit the analogy of these plates, and of those of the 

 Torpedo, to the plates of the voltaic pile, we perceive that, in the 

 Gymnotus, the batteries are horizontal and the plates vertical, whilst 

 in the Torpedo the batteries are vertical and their plates horizontal. 

 The situation of the organs is also very different in the two fishes ; 

 they extend from before the pectoral fins to the anterior part of the 

 head in the one, and from behind the pectoral fins to near the end of 

 the tail in the other. But a more important difierence exists in the 

 source of the nervous supply. In the Gymnotus the electric organs 

 are supplied by the 'rami ventrales ' of all the spinal nerves, about 200 

 pairs, that issue in the course of their extent ; some of the filaments 

 ramify upon the horizontal membranes from their cutaneous margins; 

 but the greater part of the nerves come from the deeper-seated 

 branches which descend upon the median aponeurotic partition-wall, 

 and spread upon the septa of the organ from within outwards. Yet 

 the nervus lateralis, which is dei'ived from the same cerebral nerves as 

 those which, in the Torpedo, supply the electric battei'ies, and which is 

 formed by similar proportions of the trigeminal and vagus, extends 

 the whole length of the electric organs in the Gymnotus without 

 rendering them a filament ; it is situated nearer the spine, and is of 

 larger size than usual, but Hunter* "was not able to trace any nerves 

 going from it to join those of the medulla spinalis, which run to the 

 organ." 



The proportional size of the electric organs is much greater in the 

 Gymnotus than in the Torpedo: indeed, the proper body of the 

 Gymnotus is, as it were, a mere appendage tacked on to the fore 

 part of the enormous batteries ; for the digestive and generative 

 viscera, with the respiratory and circulating organs, the brain and 

 organs of sense, — all, in fact, that constitute the proper animal, — 

 are confined to that small segment of the entire body which is 

 anterior to the electrical apparatus. The vent even oj^ens beneath 

 the head, in advance of the pectoral fins. 



The electric organs of the Mala/pterurus electricus ai'e described 

 as forming on each side the body, between the skin and the lateral 

 muscles, two thin strata, one consisting of minute lozenge-shaped 

 cells, the other of six or more fine longitudinal membranes, with a 

 delicate intervening cellular structure : they thus combine the cha- 



