The Porites are madrepores produced by a pitcher-shaped fleshy animal, with twelve short tentacula; the cells are unequally polygonal, imperfectly defined, slightly radiating by thread-like pointed rays, with prickles placed at intervals. The polypus is polymorphous or many-formed, composed of a reticulated and porous tissue, the individuals forming it being always completely united together. Externally it presents the figure of an irregular trellis-work, more or less loosely connected in its meshes. As a type of this organization, we give a figure of the Forked Porites (_P. furcata_, Fig. 78), of the natural size. The branches are generally dichotomous, that is, rising in pairs obtusely lobed. In some of the species the rays are more fully marked, and resemble a bed of miniature anemones thickly crowded together, as in _Gonispora columna_, in which the polypi have a central mouth, round which the twelve short tentacula radiate; the coral is stony, fixed, branched, or lobed, having a free surface covered with a great number of regular stars, which are highly characteristic, and cannot be confounded with those of an astrea or madrepore. [Illustration: Fig. 78. Porites furcata (Lamarck), natural size.] [Illustration: Fig. 79. Millepora alcicornis (Linn.), one-fourth natural size.] In the Tabulate Madreporides, the polyp is essentially composed of a highly-developed mural system. The visceral chambers are divided into a series of stages or stories, by perfect diaphragms or plates placed transversely, the plates depending from the walls and forming perfect horizontal divisions, extending from one wall of the general cavity to the other. In order that the reader may form some idea of the Tabulate Madrepores, one of the polyps known as _millepores_ is here represented. The millepores were first separated from the madrepores by Linnæus, along with a great number of species distinguished by the minuteness of their pores or polypiferous cells (Fig. 79), represented above, as nearly allied, and perhaps identical with Dr. Johnston's _Cellepora cervicornis_, a species found in deep water on the Devonshire and Cornwall coasts, and, indeed, all round our west coast. "A single specimen of this millepore is about three inches in height," says Dr. Johnston, "and somewhat more in breadth. It rises from a broad flattened base, and begins immediately to expand and divide into kneed branches or broad segments, many of which anastomose, so as to form arches and imperfect circles. The extreme segments are dilated and variously cut, sometimes truncate, both sides being perforated with numerous pores just visible to the naked eye, and arranged in rows; the pores circular, and level with the surface on the smooth and newly-formed parts; but in the older parts they form apertures of urceolate cells, which appear to be formed over the primary layer of cells, giving to the surface a roughish or angular appearance. The orifice is simple, contracted, with a very