THE SEA-ANEMONE AND SOME ALLIES 259 



relation between the color of the animal and the c'olor of the 

 objects in the environment. In the same situation one may 

 find all variations of uniform or mingled shades, from light 

 yellow to dark brown, a fact which of itself would indicate 

 that the animal does not depend on color-resemblance for 

 protection. 



The Coral Polyp. The only coral polyp of the North 

 Atlantic coast is Astran'gia da'nce (Fig. 130). It occurs in 

 colonies of many individuals and incrusts rocks or pebbles 



FIG. 130. Colony of Coral Polyps. Enlarged 



in shallow water, near the shore line from Massachusetts to 

 North Carolina. 



A polyp of Astrangia is about one eighth of an inch in 

 diameter and of variable length. It bears a very obvious 

 resemblance to a sea-anemone. The columnar form, the flat- 

 tened aboral surface resting on a support, and the oral end 

 with its crown of tentacles, prove the relationship. Besides, 

 examination of the interior reveals the presence of mesenteries 

 arranged very much as in Metridium. One important struc- 

 ture of Astrangia, however, is never found in the sea-anemone, 

 and that is the carbonate of lime " skeleton." This structure 



