368 PHILOSOPHY OF ZOOLOGY. 
following species of fishes. Rhinobatus electricus, Torpe- 
do vulgaris, unimaculata, marmorata and galvani*, Gymno- 
tus electricus, Silurus electricus, Tetraodon eleetricus, and 
Trichiurus Indicus. The claims of the first and last of 
these species to rank as electrical fiishes, is doubtful; those 
of the others have been established. 
The electrical organs of the Torpedo are double, and 
oceur 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 Gymmnotus 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 
Silurus electricys, the electrical organ commences at the 
head, where it is 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 Iehthyologie 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 Top. (Phil. Trans. 1816, p. 121.) 
The T. marmorata, is the species referred to by British writers. 
+ Phil. Trans. 1773, p. 481. 
