2Ut:i 



UROCHUKDA AND \'EKrEBKATA 



surface of the mouth of the c(jnimon sea lamprey is covered 

 with strong teetii and even the toufjue is fui-nished with 

 three large teeth. 13y means of the suckerhke mouth tlie 

 sea lampreys attacli themselves to the bodies of fish and, 

 with the strong teeth, rasp off bits of flesh, at the same 

 time sucking the blood. 



Just back of the mouth, on each side of the neck, is a 

 row of seven round holes (Fig. 145). These open into .short 

 tubes that lead to sacs in which the gills are situated. Con- 



sequently, in spite of the fact that the mouth of the 1am- 

 [jrey is closed, the gills are bathed by fresh sea water that en- 

 ters through the circular holes along the sides of the neck. 

 They have no backbone, but the notochord persists through 

 life. Attached to the sides of the notochord ai'c small 

 cartilaginous projections that suggest vertebra\ 



Lampreys have a rudimentary brain, a spinal cord, and 

 two eyes that ai'c without eyelids but are covered by a 

 thin transparent skin. The sea lampreys go up rivers in 

 the spring, build rude nests out of small stones, antl lay 

 their eggs there. In the autunm the }'oung return to the 

 sea. The fresh-water lampreys in Cayuga Lake, N.Y., go 

 U|) the small streams tn lay theii' eggs. 



Tlie liagfishes which belong to tliis class and greatly re- 



