PHILOSOPHY OF ZOOLOGY. 



following species of fishes. Rhinobatus electricus, Torpe- 

 do vulgaris, unimaculata, marmorata and galvani*, Gymno- 

 tus electricus, Silurus electricus, Tetraodon electricus, and 

 Trichiurus Indicus. The claims of the first and last of 

 these species to rank as electrical fiishes, is doubtful ; these 

 of the others have been established. 



The electrical organs of the Torpedo are double, and 

 occur in the fore-part of the body, one on each side of the 

 cranium ; and extend backwards as far as the gill-openings, 

 occupying the whole skin between the upper and under 

 surfaces. In the Gymnotus electricus., these peculiar or- 

 gans occupy nearly one-half of the body of the animal. 

 They are four in number, two on each side ; and extend 

 along the sides and belly, from the head to near the tail. 

 They are of unequal size ; the superior one on each side 

 being the largest. It is covered on its dorsal aspect by the 

 muscles of the back, and on its ventral aspect by the small- 

 er organ. This last reaches to the middle of the belly, and is 

 scarcely one-fourth of the size of the superior one. In the 

 Sihirus electricys* tne electrical organ commences at the 

 head, where it U thickest, aud extends along the back and 

 sides towards the tail, gradually decreasing in thinness, 

 as.it approaches the caudal extremity. 



The electrical organs in all the fishes which have been 

 examined, appear to have a reticulated cellular structure. 

 In the Torpedo marmorata, which HUNTER ( examined, 



Doubts may be entertained with regard to the propriety of constitu- 

 ting so many species, out of the Raia torpedo of naturalists, as has been 

 done by M. Risso, in his Ichthyologie de Nice, p. 18., in a great measure 

 from the colour-markings of the body ; a character in the torpedo liable to 

 considerable variation, according to Mr TOD. (Phil. Trans. 1816, p. 121.) 

 The T. marmorata, is the species referred to by British writers. 



t Phil. Trans. 1773, p. 481. 



