CARTILAGINOUS FISHES. 509 



and viscous, reminding us of serpents in their external form; they 

 have neither pectoral nor ventral fins ; their vertebrae are reduced to 

 simple cartilaginous rings, scarcely perceptible one from the other, 

 traversed by tendons, and covered by a second and more solid series of 

 rings, which surround the soft cartilaginous spine. Their gills, in 

 place of presenting the comb-like appearance of other fishes, have 

 something of the form of a purse. The lampreys may be considered 

 as the type of this family. 



The Lampreys (Petromyzon) are cylindrical, with seven gill-openings 

 on each side of the neck, forming two longitudinal lines ; mouth round, 

 armed with many teeth. The Sea Lamprey, P. marinus (Fig. 348), 



Fig. 348. The Lamprey (Petromyzon marinus). 



belongs to the Mediterranean ; it is also found in the German Ocean, 

 and the friend who supplies this note has caught it with cockle bait 

 in the South Esk, Forfarshire. In the spring it ascends the rivers, 

 where it is sometimes caught in abundance. Full-grown it is about 

 three feet long, marbled brown upon yellow ; the dorsal fins are sepa- 

 rated by long intervals ; its mouth is circular and surrounded by a 

 fleshy lip, furnished with cirri, having a cartilaginous plate for sup- 

 port ; it is provided on its internal surface with many circular rows of 

 strong teeth, some single, the others double. 



The Lamprey feeds on worms, molluscs, and small fishes ; its mouth 

 is a powerful sucker, by the aid of which it attaches itself to fishes 



