142 
NATURAL HISTORY. [NEW BUILDING. 
In some, the stomach of the animal is only provided 
with 12 slight folds, and the mouth has only 10 or 12 
tentacles. In this case the cell of the coral is provided 
with only a few slightly raised rays. Most of these animals 
live crowded together in societies forming a branched 
coral, and the cellular substance of the animal is in ge¬ 
neral not so perfectly filled with calcareous matter as in 
the former kinds; consequently the coral is of a more 
spongy or lighter texture, as in the Madrepores, Madre- 
pora , Porites , &c. (Cases 15 to 18.) 
Near these Corals must be arranged for the present, 
until their animals are better known, the Millepores ( Mil - 
lepora alcicornis of Linnaeus). The latter is remarkable 
for the rapidity of its growth and the facility with which 
it expands itself over all the different anomalous objects 
that come in its way; thus we have it covering shells, 
bottles, gorgoniae, &c., and assuming the form of all the 
things it covers (Case 20). According to Mr. Nelson, 
the animal is very different from that of any other coral, 
being quadrangular, expanded at intervals into four rays, 
and destitute of any true tentacles. 
The different kinds of these animals grow and in¬ 
crease with great rapidity, forming enormous masses 
of coral, as may be judged from a fragment on the 
south side of this Room. It is their skeletons that 
form the reefs round the islands in the Pacific Ocean, 
the growth of which has furnished such an inter¬ 
esting problem to the scientific naturalist. The spe¬ 
cimens usually shewn in collections are small indivi¬ 
duals which grow in the sheltered places among the 
rocks, where they are not exposed to the action of the 
waves, and collected before they have reached their 
proper magnitude. The form of the masses appears to 
be greatly influenced by the positions in which they have 
grown, and the size of the individuals greatly depends on 
the quantity of nourishment they are able to procure. 
This is proved by the fact, that if all the individuals of 
the same mass are equally exposed, they are of an equal 
size, but if the surface of the coral is waved, as in the 
Explanaria , (Case 13,) the individuals on the convex 
part of the mass, which could procure the most food, are 
large, while those in the concave or sunken parts are small. 
The Zoophytaria, or second order of the Zoophytes, 
