The polypary, or mass, of the armed Alcyons is either membranous or leathery, and is entirely bristled with large spicules similar to the very small ones in the tentacles of its polypes. It forms branching masses terminated by prominent tubercules thickly beset by spicules. The polypes retreat into the mass when they are in a state of contraction.
The Gorgons, which form the second family of Alcyonian zoophytes, are compound animals, consisting of a solid stem or axis either simple or branched, adhering by its base to a rock or some submarine body, and coated by a layer of a softer fleshy or horny substance exactly in the same manner as the bark covers the stem and branches of a tree. This bark or fleshy substance is filled with polypes similar to those described; however, they are shorter, their base is a little enlarged, and is turned towards the axis of the stem and branches of the Gorgon. The softer substance or bark is much developed between the polypes, and is full of spicules, of forms varying with the genera. A system of almost capillary canals traverses the soft coating and opens into the lower part of the cavity containing the viscera of the different individuals, thus affording a passage for the circulation of the nutritive juices.
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.
There is but one genus of the Coralline Gorgon, and the type of that is the common red ornamental coral of commerce found in the Mediterranean Sea only. Dr. Carpenter has discovered that the solid calcareous stem of the Corallium rubrum is made up of aggregations of spicules closely resembling those of the other Alcyonian zoophytes, but of an intense red, sometimes rose colour or whitish. The stem and branches are delicately striated along their length, and covered with a soft substance of the same colour as the stem, into which the polypes retreat when alarmed; but when fishing for food, with their eight white tentacles expanded, the red stem and branches appear as if they were studded with stars. Prof. de Lacaze Duthiers, who was appointed by the French Government to investigate the natural history of the red coral with a view to the regulation of the fishery at Algiers, found that the individual polypes are either male or female, but that the males and females are on different branches of the same coral, one branch being almost exclusively the abode of male polypes, and another of female. The eggs are fertilized by the intervention of the water. After an egg is fertilized, it is transferred to the stomach of the female, which thus serves both for digestion, incubation, and transformations of the egg. At first the egg is naked and spherical; afterwards it becomes elongated and covered with cilia. A cavity is formed in it, which opens externally, and finally becomes the mouth; it then acquires the form of a little white worm, and when it comes into the water it is very active, swimming in all directions, avoiding its comrades when they meet, rising and descending in the water with its hinder end foremost. It loses its cilia after a time, fixes itself to a rock, and acquires the form of its parent in the manner described as to other Gorgons.
