. Natural history. Zoology. CORALS. 705 between the projections, and nothing is seen over them but a thin shiny skin. Fig. 12 shows us the skeletons of two solitary corals which have thus built up their pedestals to a considerable height. The greater number of coral polyps, however, do not remain solitary, but are continually producing daughter polyps, whole families together forming great colonies, each member of which as it grows adds its own pedes- tal to the mass. All the stony corals seen in our museums are but the complicated skeletons, , the combined pedestals of polyps whose soft,
. Natural history. Zoology. CORALS. 705 between the projections, and nothing is seen over them but a thin shiny skin. Fig. 12 shows us the skeletons of two solitary corals which have thus built up their pedestals to a considerable height. The greater number of coral polyps, however, do not remain solitary, but are continually producing daughter polyps, whole families together forming great colonies, each member of which as it grows adds its own pedes- tal to the mass. All the stony corals seen in our museums are but the complicated skeletons, , the combined pedestals of polyps whose soft, jelly-like bodies have perished. In the living state these hard masses were covered by the flesh of the animal colony, as a thin layer of slimy matter. The'individual Sea-anemone-like animals lurked in the cavities, rising and expanding their search of food, but drawing them back under shelter. Fig. 12.—Thu Onp OOKAL iCaryopnyllia). The Six-rayed Corals {Hexactinia). tentacles when in whenever threatened or disturbed. Corals are usually grouped according to the number of divisions, compart- ments, or "rays'' in their bodies, each compartment, as in the Anemone, running up into the hollow axis of a tentacle. Six-rayed polyps have six tentacles or (approximately) some multiple of six, eighteen, twenty-four, forty-eight, and even more. Eight-rayed polyps have eight tentacles or some multiple of eight. Most of the six-rayed polyps live in great colonies, their skeletons produc- ing the chalky masses with which we are much more familiar than we are with the living animals. One important family of the six-rayed polyps, however, the Fungidte, or Mushroom corals, consists of single individuals. The median slit seen along the surface of the Mushroom coral (Fig. 13) indicates the position of the mouth, while the many jagged ridges that radiate out from it and give the whole the appearance of an inverted mushroom are the hard, stony ridges and partitions over which the body of the
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