NATURAL HISTORY, 
129 
ROOM III.] 
Each individual animal of these zoophytes has a simple plaited mem¬ 
branaceous bag-like stomach, with only a single orifice, like that of the 
Star-fish, and their mouth is surrounded by a more or less numerous 
series of tentacles, which search for and conduct the food that comes 
within their reach into the digestive cavity, while the animal itself is 
generally attached by its back to marine bodies, and very commonly to 
others of its own kind; the union which they form with each other is some¬ 
times so intimate that one individual cannot be injured without its being 
felt by the whole society. The hard parts of these animals have been 
all classed under the name of Corals, but the animals which form them 
are of three very different kinds, each forming a peculiar kind of skeleton 
for its protection. They are divided according to the form of the 
stomach, and the number of the tentacles, into three orders, the Zoan - 
ihiaria , Zoophytaria , (p. 131,) and Polypiaria, (p. 133). 
The first order of these animals, or Zoanthiaria, (Cases 1 to 20,) 
are so called from their resembling a flower when their tentacles are ex¬ 
panded : they are characterized by having very numerous simple ten¬ 
tacles placed in one or more series round their mouth, and their stomach 
furnished with more or less numerous longitudinal folds, which subdivide 
it into different cells. 
Some of these, as the Sea Anemonies, ( Actiniadce ,) are quite soft 
and covered with a smooth skin, so that they can only be preserved in 
a damp state. The Lucernarics only differ from these in the mouth being 
cut into four or eight lobes. A few have a hard cartilaginous outer skin, 
which is often strengthened by the deposition of earthy grains within its 
surface, as the Zoanthidce (Case 1). Some of these are crowded to¬ 
gether into a mass, as Corticifera y others are distinct from one another, 
but arise from a common surface, which is either an expanded base, as 
in Mammillifera , or a creeping stem, as in Zoanthus. By far the 
greater number of these animals, as they grow 7 , deposit in the cellular 
substance of the flesh of their back an immense quantity of earthy matter, 
which enlarges as the animal increases in size, and in fact fills up all those 
portions of the substance of the animal which, by the growth of new 7 
parts, are no longer w anted for its nourishment, and in this manner they 
form a hard and stony case, amongst the folds of which they can con¬ 
tract themselves, so as to be protected from external injury, and by the 
same means to form for themselves a permanent attachment, which pre¬ 
vents their being tossed about by every w ave of the element 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 alw 7 ays furnished with radiating 
plates, the remains of the calcareous particles which w 7 ere 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 together into a hemispherical mass like the 
Brain-stone, (Case 10,) in the form of a tree-like Coral, (Case 15,) 
