MADREPORES. 189 
defined, slightly radiating by thread-like pointed rays, with papilla 
placed at intervals. The polypidom is polymorphous or many-formed, 
composed of a reticulated and porous tissue, the individuals forming 
it being always completely united together. Externally it presents 
Fig. 73.—Millepora alcicornis (Linn.), one-fourth natural size. 
the figure of an irregular trellis-work, more or less loosely connected 
in its meshes. As a type of this organisation, we give a figure of the 
Forked Porites (2. furcata, Fig. 72), 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 
>ed of miniature anemones thickly crowded together, as in Goniopora 
columna, from the Fiji Islands, in which the polyps have a central 
mouth, round which the twelve short tentacula radiate ; the coral is 
