242 



CLASSIFICATION OF ANIMALS 



kinds of coral. Some corals secrete a horny skeleton and in 



some there is a mixture of the horny and calcareous substances. 



530. The larger anemones are considerably more complex 



Fig. 138. — Coral colonies developing on a shell. Various steps in 



the process are shown. 



than the smaller corals but certain important characters are 

 common to all and serve to distinguish this type of polyp from 

 that of the Hydrozoa. The Anthozoan polyp is distinguished 

 by the oesophagus and mesenteries. The mouth does not open 



