PRODUCTION OF ELECTRICITY 435 



parts of the lateral tail-muscles, and the electric nerves are 

 branches of the spinal nerves. 



The electric organs of the electric cat-fish, Malopterurus, 

 differ in many characteristics from those of the other electric 

 fishes. In this fish the organ consists of an almost uniform 

 layer of gelatinous tissue situated beneath the skin and extend- 

 ing all round the body, from the level of the bases of the pectoral 

 fins to the commencement of the dorsal adipose fin and the 

 ventral fin which is opposite to the dorsal. The electric layers 

 of the two sides are separated only by thin dorsal and ventral 

 partitions of fibrous tissue. The tissue beneath the electric 

 layer is continued behind into the ordinary tissue of the skin 

 so that the electric tissue seems to be derived not from muscular 

 tissue but from the skin. The organ in this case is not divided 

 into columns of plates as in the other cases, but at the same 

 time it consists of electric plates which are placed transversely 

 to the length of the body. These plates are much smaller than 

 those of the usual type of organ and are irregularly arranged ; 

 each one is flat and thin, circular in outline, and at the centre 

 of each is a funnel-shaped depression projecting backwards, to 

 the posterior end of which is attached the nerve-fibre. The 

 plates, as in other cases, contain numerous nuclei and in minute 

 structure are similar to the plates in the other cases. The 

 electric condition of the plates is, however, just the opposite 

 to that in other electric fishes, for the posterior face to which 

 the nerve is connected is positive and the anterior face is nega- 

 tive ; the posterior end of the fish is therefore positive and the 

 anterior end negative, and the current of discharge passes from 

 the tail to the head outside the fish. Still more extraordinary 

 is the innervation of the organ in Malopterurus : on each side 

 of the body the organ is supplied by a single large nerve-fibre, 

 not a single nerve but a single fibre, which branches repeatedly, 

 each ultimate branch being connected with a single plate as 

 above described. Each of these two fibres arises from a single 

 giant ganglion cell near the anterior end of the spinal cord, 

 and the fibre emerges from the spinal canal by the first inter- 

 vertebral aperture. The development of these organs is still 

 unknown, even the smallest specimens of the fish hitherto ob- 

 tained, only a few inches long, having the organs already de- 

 veloped and giving shocks like a succession of pricks when 



