FOSSIL CORALS. 61 



not to be corals at all, but demonstrated they actually 

 belong to another class, the Hydrozoa. In other words, 

 they are the remains of colonies of animals allied to 

 Sertularians, but possessing limy structures, instead 

 of the chitinous or horn-like material which composes 

 the solid parts of our " sea-firs." Professor Mosely shows 

 there is a peculiar division of labour in the polyps of 



Fig. 40. Section of " Chain-Coral " (Halysites catenulatus), showing tubes 

 (Upper Silurian formation). 



modern Millepores, some of the zoophytes catching 

 the food and others digesting it, after they have 

 received it from the catchers. This is the case in 

 Stylaster, where the food-catching zoophytes much 

 resemble the tentacles arranged round the mouth of 

 the common sea-anemone. 



The abundant recent coral Heliopora ccerulea 



