182 MORPHOLOGY OF INVERTEBRATE TYPES 



11. Remove the peristomial membrane, the ampullae of the 

 oral ossicles and all ampullae of one arm. Make a full size draw- 

 ing showing the teeth, ring of oral ossicles with ten pores for the 

 ampullae and the ossicles of the arm with the ambulacral pores 

 between them. 



(c) Cross-section of arm. 



12. Make a drawing of the prepared slide showing body wall, 

 ccelome, digestive glands with mesenteries, ampullae, ambula- 

 cral feet, radial canal, radial sinuses with the septum containing 

 the radial lacuna and the ectoneural radial nerve. 



