294 ELECTRICAL ORGANS IN FISHES. 



Maiapterums of the Nile, of which species only dissections 

 have hitherto been published (St. Hilaire, Annales de Museum, 

 torn. i. ; Eudolphi, Abhand. Berl. Akad. 1824 ; Valenciennes, 

 An. des Sci. Nat. torn, xvi.), a subjacent areolar, laminated, 

 fatty layer, has been described as a second and deeper electrical 

 apparatus ; and in the Malapterurus of Western Africa, with 

 the examination of which I am at present engaged, this 

 deeper layer exists in the form of longitudinal streaks of 

 fat between the muscles and gelatinous layer. Pacini, how- 

 ever (" Sopra 1'organo elettrico del siluro elettrico del Nilo, 

 etc.," negli Annali delle Sci. Nat. di Bologna, 1846), has shown 

 that this presumed deep electrical structure consists princi- 

 pally of fat (as it assuredly does in the species from Western 

 Africa), and probably acts as an insulator to protect the fish 

 from its own shocks ; the electrical currents being presumed 

 to pass from within outwards that is, through any point on 

 the surface of the body. 



The determination of the intimate structure of the battery 

 of Malapterurus is extremely difficult. Before Pacini, no 

 precise description of it had been attempted. He represents 

 the structure as consisting of octahedral cellules or alveoli, a 

 form which in some measure explains the variable direction 

 of the currents through the electro-motor mass. Professor 

 Ecker, in a communication contained in Siebold and Kolliker's 

 Zeitschrift fur Wissensch. Zoologie, July 1854, states that 

 Dr. Bilharz,* at present in Egypt, is engaged in the anatomy 

 of the Nilotic species, and that he conceives he has determined 

 the alveoli of the electro-motor layer to be lenticular in form, 

 with their surfaces directed forwards and backwards. He 

 would appear to have observed that they are arranged not 

 in antero-posterior series, but alternately ; so as to constitute 



* The observations of Dr. Bilharz, the Professor of Anatomy in Cairo, have 

 since been published in extenso, in a volume entitled, Das Elcdrische organ des 

 Zitterwelses ; Leipzig, 1857. EDS. 



