328 



Descriptive Zoology. 



sea anemones attach themselves to the shells inhabited by 

 hermit crabs. They thus get transportation, and are 

 more secure of getting food. In return they protect the 

 crab, for few animals care to eat so tough and nettling an 

 animal as a sea anemone. 



Coral Polyps. The coral polyps are essentially like 

 the sea anemone in their structure. But, unlike the sea 

 anemones, they are almost always in colonies. They are 

 unlike the sea anemone, too, in secreting carbonate of lime 

 at the base. The single coral makes a cup or circular 



FIG. 186. A CLUSTER OF NEW ENGLAND CORAL POLYPS. 



They secrete but little coral. 



wall, with radiating partitions, these radiating partitions 

 alternating with the mesenteries. In the colonies thej 

 individual cups fuse more or less together, making ii 

 mense masses of coral. 



Kinds of Coral Polyps. Coral polyps are usual!} 

 classed in two groups, according to the number of ten- 

 tacles. In the sea anemone the tentacles are some mul- 

 tiple of six. Some authors call these Hexacoralla. To 

 this group, besides the sea anemone, belong all the true 

 corals which produce coral reefs and islands. As is well 



