148 



COMPARATIVE ANATOMY 



hundred nerves 



and the constrictor of the gill-arches, the nerves arise from 

 the " electric lobe " of the medulla oblongata, a single branch 

 coming also from the trigeminal nerve ; in all pseudo- 

 electric Fishes, as well as in Gyrnnotus, in which over two 

 pass to the electric organ, they arise from the 

 spinal cord, and are probably in close relation 

 with the ventral cornua of the latter, which 

 are particularly well developed in the last-named 

 Fish. It is remarkable that the electric nerves 

 of Malopterurus arise on each side from a single 

 enormous lens-shaped nerve-cell, which, lying in 

 the neighbourhood of the second spinal nerve, is 

 continued into a very large primitive-fibre which 

 passes towards the end of the tail, dividing as 

 it goes. This fibre is invested by a thick sheath. 



PIG. 120. ELEC- 

 TRIC PRISMS OF 

 Torpedo mar- 

 morata. (Semi- 

 diagrammatic. ) 



Experiments have shown that all Electric Fishes are 

 proof against the electric current, with the limitation that 

 muscles and nerves even the electric nerves themselves 

 separated out from the body are capable of being excited 

 by the current. ' ' The last and most important question with regard to the 

 Electric Fishes is naturally concerning the mechanism whereby the electric 

 plates become temporarily charged with electricity. The reply to this ques- 

 tion, although probably not so difficult a one as that relating to the mechanism 

 of muscular contraction, is still far from being answered " (Du Bois-Reymond). 

 The only thing that can be stated with certainty is, that the electromotive 

 force is under the influence of the will. 



