The larvæ of the Gorgons are like ciliated eggs; they swim with their thick end foremost, and are perfectly soft. That state, however, is transitory; for no sooner do they lose their cilia and settle on a submarine substance than their lower part becomes hard, forms a solid layer on the substance, and constitutes the base for a Gorgon’s stem. A small elevation rises on it, and at the same time the upper part of the larva assumes a fleshy consistence and surrounds the elevation. These two grow simultaneously; the small elevation rises higher and higher, and its coat containing the polypes grows proportionally with it, and continues to cover it whatever form it may take, whether a branching or plumage stem, or a simple slender rod. The stem and branches are increased in thickness by successive concentric layers of horny or calcareous matter between their surface and the soft bark. The Gorgoniidæ are divided into three natural groups, the Gorgons, Isidæ, and Corallines, according to the nature of their axis. The two first agree in having stems either of a substance like cork or horn entirely or partly flexible; but the stem of the Gorgons has no joints, while that of the Isidæ is jointed. The stem of the Corallines has no joints, and is entirely stony and branching. The Gorgonia verrucosa, so common in the Mediterranean, British Channel, and the intermediate seas, is like a small shrub a foot high, with numerous branches: the cup-shaped tubercules inhabited by the polypes are irregularly distributed, and not very salient, yet enough to give the white encrusting coat a rough warty surface. In this Gorgon there is an ovary at the base of each polype: the eggs are discharged through eight small pores placed between the bases of the eight tentacles. These animals are wonderfully prolific: a Gorgon, six inches high, produced ninety eggs in one hour. The Gorgonia graminea, found on the coast of Algiers, instead of being arborescent, is thin and cylindrical throughout its whole length. The covering is white, and nearly smooth; the cups containing the polypes either have no salient border, or are deeply sunk in the coat. The Gorgons known as sea-fans live in warm seas, and are of numerous species. Not only all their branches, but all their branchlets and twigs, spread in the flat form of a fan, are soldered together so as to form a net with open meshes; the coating is thin, and the polypes are placed bilaterally. The stems and branches of the Isidæ, which form the third group of Gorgoniidæ, are composed of a series of calcareous cylinders, separated by either horny or cork-like nodes; the polypes are only born in the bark of the former. In the genus Isis the calcareous cylinders are deeply striated by straight or wavy lines. This race of animals are mostly inhabitants of warm seas; but they once lived in a colder climate. Some species of them are preserved in a fossil state in the cretaceous earth in Belgium, and in the plastic clay near London.