ACTINOZOA 29 



useful not only for defense, but for capturing crabs and small 

 fishes which form the anemone's food. 



Sea-anemones are solitary, that is, they form no permanent 

 colony. The>' have no true skeleton. There is no alternation 

 of generations. They vary in size from } inch to 2 feet in 

 diameter, and, though attached, have the power of changing 

 their position. 



The Stony Corals (Fig. 18). — The coral polyps resemble small 

 sea-anemones on a much-branched stem. The calcareous skele- 



Fig. 20. — Isopo'ra murica'ta forma prolif'era lam. End of branch, height 

 9 cm. (Vaughan, U. S. F. C. Bull., 1900.) 



ton is secreted by the ectoderm. The branched form arises 

 from the continual budding and branching from a parent stem. 

 The different forms (Fig. 19) of coral are caused by the different 

 modes of budding in the various species. Corals are of various 

 colors and some are said to be phosphorescent. 



The members of a coral colony are organically connected. 

 Each feeds himself, it is true, but no individual of the colony is 

 independent of the others. 



The size varies from that of the head of a pin to | inch, 



