374 



MANUAL OF ZOOLOGY. 



and the head is so twisted that both eyes are brought to one 



side of the body. 



The typical members of the Batides are the Skates and 



Rays, of which the common Thornback (Raia davatd) may 



be taken as a familiar example. More remarkable than the 



common Rays is the Elec- 

 tric Ray or Torpedo, which 

 has the power of discharg- 

 ing electrical shocks, if irri- 

 tated. The identity of the 

 force produced in this way 

 with the electricity of the 

 machine has been demon- 

 strated by many careful ex- 

 periments. The Torpedo 

 owes its remarkable powers 

 to two special organs the 

 " electrical organs," which 

 consist of two masses placed 

 on each side of the head, 

 and consisting each of nu- 

 merous vertical gelatinous 

 columns, separated by mem- 

 branous septa, and richly 



Fig. 143. Eatides. Raia marginata, one of 

 the Skates. Reduced one-sixth. (After 

 Gosse.) 



furnished with nerves ; the 

 whole arrangement present- 

 ing a singular resemblance 

 to the cells of a voltaic battery. There is no doubt, however, 

 but that the force wiiich is expended in the production of the 

 electricity is only nerve-force. For every equivalent of elec- 

 tricity which is generated, the fish loses an equivalent of nerv- 

 ous energy ; and for this reason, the production of the electric 

 force is strictly limited by the amount of nerve-force possessed 

 by the animal. 



In the Saw-fish (Pristis antiquorum) the body has not the 

 typical flattened form of the Rays, and the snout is elongated 

 so as to form a long sword-like organ, the sides of which are 

 furnished with strong tooth-like spines. This constitutes a 

 powerful weapon, with which the Saw-fish attacks the largest 

 marine animals. 



Before leaving the Elasmobranchii, a few words may be said 

 as to their position in the class of Fishes. From the cartilag- 

 inous nature of the endoskeleton, and the similarity between 

 the form of their gills and those of the Lampreys and Myxin- 

 pids, the Elasmobranchii were long placed low down in the 



