ECHINODEEMATA. 



Ill 



depths in the sea. Many of the deep-sea forms exhibit singular 

 modifications of structure. Some Holothurians [e.g., Sipiapta) bur- 

 row in sand or mud ; others are free. Many attain a consideral^le 

 size. 



Fi<j. 70. — Anchor-shaped spicules of 

 Synapta, and the plates to which 

 these are attached. Magniiied 

 greatly. 



