UKOCHORDA AND VERTEBRATA 



205 



but has no distinct head, no brain, and no eyes, legs, or fins. 

 It is about two inches long and is if ound buried in the sand, 

 along the shores of the Mediterranean Sea, North Sea, Eng- 

 lish Channel, our Atlantic and Gulf coasts, West Indies, coast 

 of California, etc. It is transparent, flattened from right 

 to left, and pointed at either end, hence its resemblance to 

 the head of a lance. 



The mouih is simply a slit surrounded by slender fila- 

 ments, called cirri. The blood, which is colorless, is puri- 

 fied by internal gills. No true heart is present. The 

 lancelet has no backbone, but the notochord persists 

 throughout life, and, just above it, lies the spinal cord. 



Fig. 144. — Diagram of a lancelet ; m, mouth ; gs, gill slits ; s, spinal cord ; 

 n, notochord ; i, intestine ; tf, tail fin. 



The lancelet shows its relationship to the vertebrates by 

 the possession of the notochord, spinal cord, and gill 

 slits in the walls of the phar5Tix. 



Lampreys 



Glass. — Gyelostomata 



Lampreys. — They are long, smooth, and cylindrical, ap- 

 pearing nluch like eels. In fact, they are often called " lam- 

 prey eels." There are at least twelve species in the United 

 States. They vary in length from one to two feet. The 

 mouth is circular and is formed for suction. The interior 



