206 



UROCHORDA AND VERTEBRATA 



surface of the mouth of the common sea lamprey is covered 

 with strong teeth and even the tongue is furnished with 

 three large teeth. By means of the suckerlike mouth the 

 sea lampreys attach themselves to the bodies of fish and, 

 with the strong teeth, rasp off bits of flesh, a,t 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 giUs are situated. Con- 



Fl6. 145. — Sea lamprey. 



sequently, in spite of the fact that the mouth of the lam- 

 prey 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 are small 

 cartilaginous projections that suggest vertebrae. 



Lampreys have a rudimentary brain, a spinal cord, and 

 two eyes that are without eyeUds but are covered by a 

 thin transparent skin. The sea lampreys go up rivers in 

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

 their eggs there. In the autumn the young return to the 

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

 up the small streams to lay their eggs. 



The hagfishes which belong to this class ard greatly re- 



