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 





. 7j. 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 (P. furcata, Fig. 7 2), 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 Goniopora 

 columna, from the Fiji Islands, in which the polyps have a central 

 mouth, round which the twelve short tentacula radiate ; the coral is 



