128 COMPARATIVE AN ATOM \ r . 



As this disk, which, as already mentioned, is to be looked upon as 

 metamorphosed muscle-substance, becomes inseparably fused with 

 the nerve- plate lying close to it, it follows that the electric plate is 

 not a uniform structure, as was formerly believed, but is to be 

 regarded as having arisen out o( two tissue-elements. The com- 

 partments are not entirely filled by the electric plates ; a space 

 tilled by gelatinous tissue (Fig. 103, G], or sometimes only 

 by a fluid, always remains in the upper (Torpedo) or anterior 

 (Gymnotus, Malapterurus) side of each compartment along 

 the wall separating it from the next. The side of the electric 

 plate on which the nerve branches out is negative at the 

 moment of discharge, while the opposite side is positive, and thus 

 the different arrangements of the parts in Gymnotus and 

 Malapterurus render it clear that the electric shock must pass 

 in different directions in these Fishes : thus in Malapterurus it 

 passes from the head to the tail, but in the contrary direction in 

 Gymnotus. In Torpedo the discharge passes from below upwards. 



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 question, 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. 



BIBLIOGRAPHY. 



BABUCHIN'. Uebers. dor ncucren Untersuchungcn uber Entwickhmg, &c., der elektri- 

 schcn und pseudoelektriscficn Organe. Arch.f. Anat. und Physiol. 1876. 



KCKER, A. Entioickl. der Nerven des elektr. Organs von Torpedo Galv. Zeitschr. fiir 

 wiss. Zoot. Bd. I. 1848. Unters. zur Ichthyologie. Freiburg, 1857. 



JiRYMOND, E Du Bois. Gcsammelte Abhandlungcn zur ally. Muskel- und Nerven- 

 physik. Bd. II. 



