January 19. 1893 



NA TURE 



273 



electromotor properties ; on the contrary the loosened 

 and differently arranged elements of the changed muscles 

 are more capable of producing electric currents. In that 



. — Transverse section through the body of Malapterurus with a parasite 

 in the electric organ. 



State of development which has still quite an occasional 

 character, it seems only necessary to assume that under 

 certain favourable circumstances the fish while trying to 

 catch a prey or to defend itself against an enemy in the 

 sudden excitement becomes aware of its electric power 

 hitherto unknown to itself On perceiving the advan- 

 tage of the electric power in the struggle of life the fish 

 might begin to use it regularly and to develop it gradually 

 to perfection in its descendants ; just as a man might one 

 day perceive that he is endowed with the power of hyp- 

 notism, consequently learns to use it and gradually 

 improves it. 



But now it is necessary to consider also the electric 

 Shadfish of the Nile, the Malapterurus electricus, a 

 powerful fish of very peculiar structure, which places it 

 in quite a different category from the electric fishes 

 already mentioned. A transverse section of the whole 

 fish (Fig. 4) shows the difference at once. The body of 

 the animal is enveloped in a very thick electric skin, con- 

 stituting one electric organ. Muscular tissue is nowhere 

 deficient, other histological elements must therefore have 

 furnished the material for the electric plates, which are 

 packed very close in lozenge-shaped compartments of 

 the skin. 



In my opinion the plates are nothing else than modi- 

 fied cells of the cutaneous glands which are plentiful in 

 the remainder of the skin. The precise proof of that 

 statement ought to be furnished by a complete investiga- 

 tion of the development of the animal, which as yet is 

 quite unknown. But the differences lietween the two 

 kinds of electric organs are so great that we are surely 

 entitled to separate the muscular from the cutaneous 

 electric organs. 



Assuming that the origin of these cutaneous batteries 

 differs from those developed from muscle, we cannot 

 wonder that their functions also differ in most important 

 points. The electric current passes through the body in 

 a direction the opposite of that in other electric fishes. 

 There are only two electric nerve fibres, one on each 

 side, which divide and subdivide until they give off more 

 th.-in two million branches. We shall see that these two 

 nerve fibres are not true axis cylinder processes of 



NO. i 2 12, VOL. 47] 



ganglion cells. Before making a more detailed reference 

 to these interesting elements it may not be amiss to point 

 out in the section shown in Fig. 4 the existence of an 

 intruder, a specimen of the so-called Filariapiscium^ 

 which had taken up its abode in the electric organ 

 itself. This proves that animals can become accus- 

 tomed to strong electric currents without receiving 

 injury, and it suggests that the immunity of electric 

 fishes against their own currents and that of their 

 young in utero (Torpedo) is a faculty acquired by 

 gradual training. 



The construction of the single electric nerve fibre 

 in Malapterurus resembles to a surprising extent 

 that of an electric cable on a minute scale. We see 

 the tiny nerve fibre like the central wire of the cable 

 surrounded by a little non-conducting material and 

 held in situ by a sort of network ; the whole being- 

 enveloped in an enormous mass of connective tissue 

 sheaths just like a cable protected externally by 

 numerous layers of strong material. Fig. 5 shows a 

 transverse section of the central part only to render 

 the details of the round fibre and supporting net- 

 work more distinct. If we follow this single fibre 

 inwards to its origin in the central nervous system 

 we are led to a si?igle ganglion cell from which the 

 single fibre arises. There is one cell on each side of 

 the cord, therefore just two cells in all ; whereas 

 in Mormyrus, which has the smallest number of " 

 electric cells in the fishes with electric organs of 

 muscular origin, the cells must be estimated at more 

 than 1500. The position of the two cells in the 

 spinal cord of Malapterurus reminds one of Clarke's 

 column in the cord of higher vertebrates where the 

 cells differ in certain particulars from the motor cells. 

 As already stated there is only one cell on each side, but 



Fig. 5. — Transverse section of the central part of the electric nerve of 

 Malapterurus. 



that is a giant of its race. There is no real axis cylinder 

 arising from the cell, but in place of it branched proto- 

 plasmic processes join and form a kind of perforated 



