XIV] 



ECHINOIDEA 



351 



B. 



FIG. 164. Sections through parts of Echinus esculentus. 



A section at right angles to the plane of the madreporic plate x 16. 

 From Chadwick. 1. Madreporic plate. 2. Pores in the same. 



3. Madreporic vesicle. 4. Ampulla of madreporic plate or dilatation of 

 stone-canal into which the pores open. 5. Madreporic tube. 6. Geni- 

 tal stolon. 7. Axial sinus. 



A section at right angles to an ambulacral area. 1. Eadial nerve-cord. 

 2. Eadial perihaemal canal. 3. Eadial water-canal. 4. Epineural 

 canal. 5. Ampulla. 6. Cavity of tube-foot. 7. Ambulacral plate. 

 8. Boss for articulation of spine. 9. Spine. 10. Muscles which move 

 the spine. 11. Ectoderm. 



