256 VERTEBEATA: PISCES OR FISHES. 



the mouth, nostrils, and gill-openings on the under sur- 

 facethe eyes being on the upper surface. Their teeth 

 are of a definite form, and set together like a pavement, 



FIG. 296. 



Teeth of a Ray. 



and are suited to crushing shell-fish, upon which they 

 mainly feed. 



The Rays vary in size from those two or three feet long to those 

 known as Vampires, which attain the most wonderful dimensions. 

 One of these taken off Messina weighed over half a ton. Another 

 taken off Barbadoes is said to have required seven yoke of oxen to 

 draw it ! And Levaillant tells us of one which was twenty-five feet 

 long and thirty feet wide ! 



The Rays known as Torpedoes are famous for their 

 electric or galvanic power. These have the space be- 

 tween the pectorals, head, and the branchiae, on each side, 

 filled with a singular apparatus formed of little mem- 

 branous tubes placed close together, and subdivided by 

 horizontal partitions into small cells filled with mucus, 

 and traversed by nerves. In this apparatus resides the 

 electric power. Yiolent shocks are received by coming 

 in contact with these fishes when alive. 



The famous Saw-fishes (Fig. 298) are selachians, which 

 in some respects are like the Rays, but their body is very 

 much narrower, and more like that of the Sharks, and 

 they have one feature which at once distinguishes them 



