114 LABORATORY WORK. 



tion of carmine or Prussian blue). What happens to 

 the ampullae and ambulacra? Part the ambulacra and 

 follow the colored radial canal to the region of the mouth, 

 and see how this is surrounded by a ring-canal. Are 

 stone-canal, racemose vesicles, or Polian vesicles filled 

 with the fluid? Insert the radial and ring canals, ampullae, 

 and ambulacra in the drawing of the stone-canal, etc. 



Beneath the radial canal is a thickening of the skin, the 

 radial nerve, which connects with a circumoral ring-nerve 

 just below the ring-canal. 



