56 INTRODUCTION. 



from the alternation of these different laminae an 

 analogy is established with the common galvanic 

 pile; and that thus this animal can give and with- 

 hold at pleasure electric shocks, as means of de- 

 fence, and also as weapons wherewith to stun its 

 prey. 



In the otherwise excellent representation which 

 M. Geoffrey supplied of this fish, in the 1st volume 

 of the Annales du Musee, it appears covered with 

 scales. This, however, is quite contrary to the fact, 

 and opposed to an important law in the galvanic 

 physiology of those fishes which are possessed of 

 electrical powers. All of these, remarks M. Valen- 

 ciennes, which are as yet known, have neither 

 scales nor spines upon their body. The Torpedo, 

 Gymnotus, and this Silurus, have the skin smooth ; 

 and even the Tetrodon electricus furnishes an addi- 

 tional example. Although most of the genus Tetro- 

 don have the surface actually bristled, so that they 

 have received the popular name of Sea-hedgehogs, 

 yet a few are included which are destitute of osseous 

 spines, and possessed of a smooth skin ; and to this 

 class the electric animal belongs. 



The electrical powers of this fish have not hither- 

 to been the subject of any accurate experiments. 

 Adanson only remarked, that it did not appear 

 to differ sensibly from the shock of the Leyden 

 phial; and the account of Richard Jobson is to the 

 effect, that when using a net in the river Gambia, 

 they captured, among other fishes, one like an 

 English bream, but broader and thicker, which. 



