ECHINODERMATA. 



Ill 



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

 modifications of structure. Some Holothurians {e.g., Synapta) bur- 

 row in sand or mud ; others are free. Many attain a considerable 

 size. 



Fig. 70. — Anchor-shaped spicules of 

 SyiMpta, and tlie plates to which 

 these are attached. Magnified 

 gi-eatly. 



