150 ANIMALS 



the lime is deposited in great quantities. This is notably true 

 of the corals, which are closely related to hydra. Many 



FIG. 75. A common type of massive coral, Solenastrea, from Bermuda. Each 

 cup is formed by a polyp and radial septa in the cups indicate the pairs of 

 mesenteries of the polyp. Slightly reduced. 



worms live in hard, limey tubes which they secrete. The shell 

 of the mollusc originates in the same way, but here it forms part 

 of the body of the animal. 



