SECT. vi. ECHINODERMATA. 187 



internal cavity by the cilia with which it is lined. The 

 mouth of the Sipunculus is a kind of proboscis with a 

 circular fringed lip and two contractile vessels, supposed 

 to serve for raising the fringes. An alimentary canal 

 extends to the end of the animal, turns back again, 

 and the intestine ends in a vent near the mouth, so 

 that the creature need not leave its burrow and expose 

 itself to enemies in order to eject the refuse of its food. 

 The locomotive larval zooids from the rose-coloured 

 eggs undergo two metamorphoses; at last the young 

 Sipunculus unites with the zooid, and no part is thrown 

 off. 



