42 ANIMAL FORMS 
colonies are produced (Fig. 26). At the same time the 
outer layer of the body is continually forming a skeleton 
which encloses the colony as a sheath, except at the ter- 
mination of each branch, where the mouth and tentacles 
are located. In certain species—for example, the sea pens 
(Pennatula) and sea fans (Gorgonia)—a skeleton may be 
Fig. 26.—Small portions of coral colomes, with some of the polyps expanded. 
formed of myriads of lime spicules, somewhat like those 
of the sponge, which are bound together by the fleshy 
substance of the body; but the skeleton of most of the 
common forms in the ocean, and the coral found in 
general collections, is stony. According to their method 
of branching, such specimens have received various popu- 
lar names, such as brain, stag-horn, organ-pipe, and fun- 
gous corals. 
