CORAL ISLANDS AND C ORAL. 269

all there is to it. Around this mouth are long little feelers or tentacles
that play in and out, taking up and then expelling the matter. The
sea water leaves behind its caleareous or limy matter, which is de-
posited in very thin strips in the sack or body. The lime-matter left
behind is the coral which keeps increasing as the polyp begets children
‘in the form of buds; for these develop into coral-making factories,
and go to work very soon.

“The coral-buds are sometimes sprouted sidewise, and then the
coral branches out like a tree; or the polyps may take a notion to
arrange themselves so as to form a convex surface, and keep growing
that way, in which case you have a kind of dome. Coral is very
beautiful in some of its colors and shapes. Its forms have been likened
to fans and even flowers, but the gardens that these bloom in are at the
bottom of the sea. Sometimes coral is shaped like a vase covered with

a flower-like growth.”

The captain paused. :

“ Well,” said Siah, who was quite a utilitarian, “ these are pretty; but
what good do dey do?”

“In various ways they are useful, and here is one: What we call
carbonic acid in the atmosphere is very essential, but it may be ex-
cessive, and so the plants, trees, gardens and forests take it up. This
carbonic acid is in the‘rivers in the form of lime-salts, and that too
much may not get into the sea, it is thought that the little polyp has
its mission; taking up the limy water and retaining the lime as coral.
That, though, is only an opinion.” |

“And then they build islands, uncle, don’t they? They are useful
that way.”

“Yes, many islands and reefs are built in that way. Off Australia is a
reef with occasional gaps, over one thousand miles long. Some are ring-
like, and the people of the Maldive Islands call them atolls. Matter will