RAYS. 339 



caudal always, present. Anterior nasal valves confluent into a 

 quadrangular lobe. An electric organ composed of vertical 

 hexagonal prisms hctween the pectoral fins and the head. 



" Electric Eays." The electric organs with which these 

 fishes are armed are large, flat, uniform bodies, lying one on 

 each side of the head, bounded behind by the scapular arch, and 

 laterally by the anterior crescentic tips of the pectoral fins. 

 They consist of an assemblage of vertical hexagonal prisms, 

 whose ends are in contact with the integuments above and 

 below ; and each prism is subdivided by delicate transverse 

 septa, forming cells, filled with a clear, trembling, jelly-like 

 fluid, and lined within by an epithelium of nucleated cor- 

 puscles. Between tliis epithelium and the transverse septa 

 and walls of the prism there is a layer of tissue on which the 

 terminations of the nerves and vessels ramify. Hunter 

 counted 470 prisms in each battery of Torpedo marmorata, 

 and demonstrated the enormous supply of nervous matter 

 which they receive. Each organ receives one branch of the 

 Trigeminal nerve and four branches of the Vagus, the former, 

 and the three anterior branches of the latter, being each as 

 thick as the spinal chord (electric lobes). The fish gives the 

 electric shock voluntarily, when it is excited to do so in self- 

 defence or intends to stun or to kill its prey ; but to receive 

 the shock the object must complete the galvanic circuit by 

 communicating with the fish at two distinct points, either 

 directly or through the medium of some conducting body. 

 If an insulated frog's leg touches the fish by the end of the 

 nerve only, no muscular contractions ensue on the discharge 

 of the battery, but a second point of contact immediately 

 produces them. It is said that a painful sensation may be 

 produced by a discharge conveyed through the medium of a 

 stream of water. The electric currents created in these fishes 

 exercise all the other known powers of electricity : they 

 render the needle magnetic, decompose chemical compounds, 



