CORALS 57 
mind spending a good time in your search. But you 
won’t mind the passage of time if you are en- 
thusiastic. 
Corals form a very important group of the Ceelen- 
terata. I have no doubt you have all seen pieces 
of what is called “‘ coral,” which, however, is but a 
mass of shells of carbonate of lime which the busy 
little builders once inhabited. Corals are closely 
Rastrites peregrinus | Monograptus priodon Didymograpsus Mur - 
(Upper Silurian). (Upper Silurian).  chisonit (Ordovician). 
Fia. 9.—GRAPTOLITES. 
related to sea-anemones, but they are very small 
animals ; they possess tentacles, which move about 
in water and catch food; they also have mouths, 
gullets, and internal cavities in their soft bodies 
where food is digested. They extract carbonate of 
lime from water, and secrete it from their bodies as 
shells or skeletons. These shells become cemented 
together when corals live in colonies, and coral reefs 
are built up in this way by millions of the little 
8 
