48 FLORIDA REEFS. 
io-neous mass of materials which formed its earliest condition, their inves- 
tigation mingles with that of the astronomer, and we cannot trace the 
limestone in a little coital without going back to the creation of our solar 
system, when the worlds that compose it were thrown off from a central 
mass in a gaseous condition. 
When the coral has become in this way permeated with lime, all parts 
of the body are rigid, with the exception of the upper margin, the 
stomach, and the tentacles. The tentacles are soft and waving, projected 
or drawn in at will ; they retain their flexible character through life, and 
decompose when the animal dies. For this reason the dried specimens 
of corals preserved in museums do not give us the least idea of the living 
corals, in which every one of the millions of beings composing such a 
community is crowned by a waving wreath of white or green or rose- 
colored tentacles. 
As soon as the little coral is fairly established and solidly attached to 
the ground, it begins to bud. This may take place in a variety of ways, 
dividing at the top or budding from the base or from the sides, till the 
primitive animal is surrounded by a number of individuals like itself, of 
which it forms the nucleus, and which now begin to bud in their tiu-n, 
each one surrounding itself Avith a numerous progeny, all remaining, how- 
ever, attached to the parent. Such a community increases till its individuals 
are numbered by millions ; and I have myself counted no less than fourteen 
millions of individuals in a coral mass of Porites (Plate XVI.) measuring 
not more than twelve feet in diameter. The so-called coral heads, which 
make the foundation of a coral wall, and seem by their massive character 
and regular form especially adapted to give a strong, solid base to the 
whole structure, are known in our classifications as the Astroeans, so named 
on account of the star-shaped form of the little pits crowded upon their 
surface, each one of which marks the place of a single more or less 
isolated individual in such a community. 
Thus firmly and strongly is the foundation of the reef laid by the 
Astra3ans (Plate IV.) ; but we have seen that for their jjrosperous growth 
they require a certain depth and pressure of water, and, when they have 
brought the wall so high that they have not more than six fathoms of 
water above them, this kind of coral ceases to grow. They have, however, 
prepared a fitting surface for different kinds of corals that could not live 
in the depths from which the Astraeans have come, but find their genial 
