324 A COURSE ON ZOOLOGY. 



grows to a length as great as ten feet. The flesh is 

 used as food, caviare is prepared from the eggs, while 

 the interior of the swimming-bladder furnishes isinglass. 



CYCLOSTOMATA. 



The members of this group differ from the true fishes 

 in having no jaws, no paired fins, no scales, and they 

 possess gill-pouches that act like lungs. The lamprey 



FIG. 283. 



LAMPKEV (Petromyzon marinus). 



and the hag-fish are examples ; the first a marine, the 

 second a fresh-water species. They have round mouths, 

 in which the tongue works like a piston, so that they 

 can attach themselves to the skin of fishes and suck not 

 only blood but flesh. 



