92 VERTEBRATE ZOOLOGY 



mouth or oral funnel, which is lined with chitinous teeth to help in 

 securing a firm hold. The flesh of the fish is then lacerated by the 

 rasping tongue and swallowed. Ultimately, of course, the prey is 

 killed and then feeding may be carried on at leisure. While they are 

 feeding, the mouth is closed and respiration is carried on by incurrent 

 and excurrent streams of water through the branchial clefts. The 

 branchial part of the pharynx is cut off from the alimentary part and 

 ends blindly, so that respiration is independent of the mouth. 



The fresh-water lampreys are lovers of rapid waters and are often 

 seen in rocky streams attached by the mouth to stones. 



The Petromyzontia represent an evolutionary stage a step or two 

 beyond that occupied by the Myxinoidea and a formal list of their 

 characters furnishes an interesting comparison with those given 

 above for the latter. The characters of the adult lamprey are shown 

 in Fig. 49. 



. 1. The mouth is provided with a perfect oral funnel, used as a 

 vacuum cup, and armed with chitinous teeth. 



^ 2. The naso-pituitary sac ends blindly beneath the brain. 



,3. N6 buccal tentacles. 



.4. Branchial skeleton a stiff intricate basket of cartilaginous bands 

 and rods. 



.5. Vertebral arches extend well forward from the tail and are of a 

 more advanced structure than in the myxinoids. 



6. A rudimentary spiral valve is present in the intestine, probably 

 indicating a specialization of the intestine paralleling that seen in the 

 sharks and certain other fishes. 

 7. No distinct mucous sacs. 



8. The cerebral hemispheres are distinct and a band-like cerebellum 

 is recognizable. 



9. Eyes well developed, with good muscles and nerves. 



J.O. The median fin system is specialized into two dorsal fins and 

 a caudal fin. 



f 11. There are two semicircular canals in the inner ear, a condition 

 intermediate between that seen in the myxinoids and that in the 

 true fishes, where three canals are always present. 

 12. " Tongue" apparatus less elaborate. 



13. Number of gill-slits uniformly 7, more primitive than fishes, but 

 more specialized than in some of the myxinoids. 



14. Pronephros non-functional in the adult. 



