Coral                             103
	like the bones of vertebrates, and is not built up as bees build a honeycomb as is popularly believed. The pits or depressions on a branch of coral represent the places where the coral colonists once grew. Coral is a common sub­marine feature in low latitudes all around the globe, but the gem or precious coral, Corallium rubrum, formerly called Corallium nobile, comes almost exclusively from the Mediterranean Sea off the African, Corsican, and Sicilian coasts. A wild-rose pink is the particular shade most highly favoured. The Corallium rubrum, the only species utilised and valued to any extent for jewelry, belongs to the family Gorgonidae of the group Alcyonaria. The skeleton of a colony of Corallium rubrum is found to be cemented firmly by a disc-shaped foot to any dense natural or foreign object on the sea bottom, as a stone, cannon-ball, bottle, or, as is recorded in one case of fact, a human skull. The branches seldom exceed a foot in length and an inch in diameter. A curious characteristic of coral is, that it grows always perpendicular, or approximately, at a right angle to the surface to which it is attached— downward, if its foothold is on the under face of a rock.