68 NATURAL HISTORY. [n. ZOOL. GAL. 
the animal which, by the growth of new parts, are no 
longer wanted for its nourishment, and in this manner 
they form a hard and stony case, amongst the folds of 
which they can contract themselves, so as to be pro¬ 
tected from external injury, and by the same means to 
form for themselves a permanent attachment, which pre¬ 
vents their being tossed about by every wave of the ele¬ 
ment in which they live. The stony substances so formed 
are called Corals , and their mode of formation causes 
them exactly to represent the animal which secretes 
them ; the upper surface is always furnished with radiat¬ 
ing plates, the remains of the calcareous particles which 
were deposited in the longitudinal folds of the stomach 
before referred to, and as these plates do not usually 
reach to the centre, there is almost always a vacant space 
in the middle between them. 
The structure of these animals, and of the corals they 
form, is most easily studied in those kinds which are 
simple and separate from each other, as the Fungia , 
(Case 2,) and if these are understood, the structure of 
the other kinds will readily be made out, for they are all 
formed in the same manner, although they are much 
modified in their outward form by being crowded to¬ 
gether into a hemispherical mass like the Brain-stone, 
(Case 10,) in the form of a tree-like Coral, (Case 15,) or 
of an expanded frondose mass, like the Explanaria. All 
these variations result from the manner in which the 
animal emits from the whole surface, or from a particular 
part of the sides of its body, the bud by which the new 
individuals of the general mass or society are produced. 
In the greater part of these animals, the stomach is 
furnished with numerous folds, leaving many plates in the 
cells of the coral, and the mouth has generally equally 
numerous tentacles, as in the Sea Anemonies, or Actinice. 
In some, as the Fungia , Turbinolia } ^\^. Q/a£Abza,(Case2,) 
the animals are simple and solitary, and not spontaneously 
divided, so that the coral only offers a single cell. In 
others, where the animals live in societies, the mouth 
often contracts on the side and separates of its own 
accord gradually into two or more mouths; it then pro¬ 
duces as many separate cells, which are separated or 
forked where the contraction took place. In some 
