ROOM III.] NATURAL HISTORY. 69 
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 
Expianaria , (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 division of the Zoo¬ 
phytes, (Cases 21 to 28,) are easily known from the other 
kinds by having only six or eight tentacles, furnished 
with one or more series of short processes on each 
side. Their stomach ends in six or eight elongated 
processes, which are considered as the oviducts. One 
genus of these animals ( Cornularia , Case 21) is said 
to have a horny external skin like the Tuhularia , into 
which the animal is retracted for protection. There are 
some other genera which are said to have a hard carti¬ 
laginous external skin like the Zoanthi , as the Telesto . 
One genus has a similar tough skin, which is at length so 
hardened by the deposition of calcareous matter within 
its substance as to become a hard coral. This genus of 
animals live in groups side by side, and as they increase in 
size form shelly tubes, which has caused them to be called 
Organ Coral ox Tubipora (Case 21). At certain intervals 
the animals contract themselves into their tubes, and 
bend out the soft part of the outer skin of the body near 
the head, so that it forms a broad collar round the end 
of the harder tube ; and as the different animals of the 
same group of tubes generally perform this action simul- 
