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 turn, each one surrounding itself with a numerous progeny, all remaining, however, 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 measuring not more than twelve feet in diameter. These are the so-called Coral heads which form the foundation of a Coral wall, and their massive character and regular form seem to be especially adapted to give a strong, solid base to the whole structure. They are known in our classifications as the Astraeans, so named on account of the star-shaped form of the little pits that are crowded upon the surface, each one marking the place of a single individual in such a community. Thus firmly and strongly is the foundation of the reef laid by the Astraeans; but we have seen that for their prosperous 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 home nearer the surface; such a home being made ready for them by their predecessors, they now establish themselves on the top of the Coral wall and continue its growth for a certain time. These are the Mandrinas, or the so-called Brain-Corals, and the Porites. The Mandrinas differ from the Astraeans by their less compact and definite pits. In the Astraeans the place occupied by the animal in the community is marked by a little star-shaped spot, in the centre of which all the partition-walls meet. But in the Mandrinas, although all the partitions converge toward the central opening, as in the Astraeans, these central openings elongate, run into each other, and form waving furrows all over the surface, instead of the small round pits so characteristic of the Astraeans. The Porites resemble the Astraeans, but the pits are smaller, with fewer partitions and fewer tentacles, and their whole substance is more porous.