580 PHYLUM CHORDATA : CLASS CYCLOSTOMATA 



selves to living fishes, and scrape holes in their skin, 



Fig. 327. — The lamprey {Petromyzon marinus). 



I. The entire animal ; note the seven gill-slits of which the first is 

 marked g.s., the nostril n., and the unpaired median fins. 

 II. Ventral aspect of the head ; «./., upper teeth; /.^, lower 

 teeth ; p., the piston in the mouth. III. Upper surface of the 

 head ; n., the nostril with the pineal groove behind it ; e., the 

 eye. 



As their names suggest, they also fix their mouths to 

 stones, and some draw these together into nests. 



The spawning takes place in spring, usually far up rivers. 



