January 19, 1893] 



NATURE 



271 



ON THE ORIGIN OF THE ELECTRIC NERVES 

 IN THE TORPEDO, GYM NOT US, MORMY- 

 RUSAND MALAPTERURUS. 



T^HE subject of this communication may seem remote 

 -■■ and uninteresting, but it will not be difficult to 

 show that questions of the highest importance for phy- 

 siology, anatomy, and the Darwinian theory are closely 

 related to those touching the structure of the electric 

 organs of certain fishes and the laws of their functions. 



The fact that the body of an animal should become a 

 complete electrical apparatus acting at the will of its 

 owner induces us to inquire how this extraordinary result 

 has been attained ; that is, to investigate the origin of 

 the electric organs of fishes, and the manner in which 

 the animal throws them into action. We shall see that 

 in pursuing both lines of enquiry we open far-reaching 

 views into regions as yet unknown. 



According to the present state of our knowledge there 

 ■can be no doubt that most of the electric organs hitherto 

 discovered are of muscular origin. It is not my intention 

 to dwell on this transformation of muscular tissue, but it 

 may nevertheless prove interesting to cite an example of 



The well-known electric eel of America, Gymnotus 

 eleciricus, has only the external shape of an eel, and is in 

 reality a very short fish, carrying very powerful electric 

 organs in a long tail springing from a very short rump. A 

 transverse section of the tail shows that a part of the 

 muscle is changed into electric organs, while another 

 remains unchanged. 



In the different kinds of electric skates — Torpedinidae 

 — the electric organs are developed from muscles, which 

 originally belong to the branchial arches and the arch 

 of the lower jaw. 



When we look to the nerve apparatus which enables 

 the fish to throw the electric organs into action by a 

 voluntary impulse, we find in every case wonderfully 

 developed ganglion cells from which the impulse is trans- 

 mitted directly to the electric batteries. Such a coinci- 

 dence certainly cannot be the result of mere chance. 

 But beyond the invariable presence of large ganglion cells 

 as the starting points of electric nerve fibres there is 

 very little uniformity in the arrangement of these elements 

 in the different sorts of electrical fishes ; on the contrary, 

 there are most remarkable and striking differences 

 not only in the position but also in the number and in the 



-Xraniverse section of the tail of Morinytus cyprinoides. 



Fig. 2.— Ganglion cells from roots of electnc nerves of Torpedo. 



the completeness with which such transformation can 

 take place ; I refer to the Mormyrus — the so-called pike 

 of the Nile — a fish which has only of late been sufficiently 

 known to possess electric power. A transverse section of 

 the tail of any ordinary fish shows scarcely anything more 

 than the vertebral column, muscles and their tendons, 

 attached to the bones. On the other hand, a transverse 

 section of the tail of Mormyrus (Fig. i) shows no con- 

 spicuous muscles, but in place of them electric tissue 

 filling up the entire space occupied by muscles in ordinary 

 fishes. Of the muscular apparatus there is nothing 

 left except the longitudinal tendons passing outside the 

 electric organs from muscles placed anteriorly. If these 

 tendons were cut across the Mormyrus would be unable 

 to move its tail. 



Omitting the complicated arrangement of histological 

 elements in this modified muscular tissue in the different 

 electrical fishes— which could not be sufficiently explained 

 without a large number of illustrations— it may be suffi- 

 cient to state that a kind of swelling loosens the molecular 

 elements of the muscles and allows them to be settled 

 agjain in a very regular but quite new form. 



NO. I 2 12, VOL. 47] 



appearance of these nerve centres. It is to be hoped 

 therefore, that some important views regarding the 

 character and functions of ganglion cells in general may 

 be suggested by their study. 



In the Torpedo the electric ganglion cells — being in 

 vast numbers — form a bean-shaped mass in the medulla 

 ! constituting the well-known electric lobe. It represents 

 1 modified motor centres of the vagus nerve ; anteriorly it 

 is covered by the cerebellum, but emerging from beneath 

 I that organ, the lobe increases rapidly where the largest 

 I electric nerve leaves the medulla. Lower down its size 

 again diminishes, where it gives rise to the fourth electric 

 nerve and terminates quite free in a blunt point on each 

 side. On counting the ganglion cells in a complete series 

 of sections one finds the number to be about 54,000 — a 

 number that can be found to nearly corresp>ond with the 

 fibres in the electric nerves that arise from them. A trans- 

 verse section of the medulla, close to the spot where the 

 roots of the electric nerves are gathering, shows the so-called 

 axis cylinder processes of the cells entering the roots to 

 form the nerves. This is seen in Fig. 2— a photogram taken 

 from nature like all the other illustrations of this paper. 



