FISHES 



91 



provided with electric organs, by which other fishes may be killed 

 or rendered powerless. 



ROUND-MOUTHS (Cyclostomes) 



The lowest Vertebrates which have any claim to be included 

 among the fishes are the Round- Mouths or Cyclostomes, including 

 the Lampreys and Hags, which have a 

 wide distribution in both hemispheres. 

 They are eel-like creatures, remarkable for 

 the absence of a lower jaw. so that they 

 are unable to bite in the ordinary sense of 

 the word. Notwithstanding this, they are 

 essentially carnivorous in habit, and prey 

 upon other fishes. If, for example, we 

 examine the common fresh-water Lampern 

 iyPetromyzon fluviatilis) (see vol. i, p. 291), 

 or the larger Sea Lamprey {P. marinus), 

 we shall find that the mouth opens in 

 the middle of a large bell-shaped sucker, studded with horny teeth. 

 A muscular projection, the tongue, also provided with powerful 

 teeth, can be alternately protruded from and withdrawn into the 



^'&- 373- — Suctorial Mouth of 

 Lamprey [Petrotnyzon) 



Fig. 374. — Hag- Fish {Myxine glutinosa) 



mouth. The sucker is firmly attached to the prey, and the tongue 



is then used as a rasp for scraping away parts of the flesh (fig. 373). 



Still more specialized is the Hag- Fish {Myxine glutinosa) 



(fig. 374), in which the degenerate and useless eyes are sunk 



