Notes on the nature of the Axis of the Gorgonia verrucosa.
By R.Q. Couch, Esq., M.R.C.S.L.
Whatever opinion is entertained regarding the polypidoms of the hydroid, helianthoid, and molluscan zoophytes, no doubt seems to exist among authors but that the stony and horny axes of the asteroid are inorganic. Lamarck, as quoted by Dr. Johnston, says distinctly that they are inorganic, containing neither vessels nor the least portion of the body of the polypes, but formed of matter excreted by them, and afterwards thickened, solidified and cleared by affinity; and to this Dr. Johnston in some measure subscribes. Ellis appears to have entertained an opposite opinion, which he has supported by facts and observations on different species. As the Gorgoniae are the only species of this order found on the Cornish coasts, with polypidoms, the following observations will be confined to them, or rather to the Gorgonia verrucosa, which is very common, and has afforded an extensive means of observation.
The hard part, or polypidom, of this order, has a new and remarkable position when compared with all the others; instead of being external and affording both support and shelter to the polypes, it is internal and not immediately connected with them. In many species it is stony, while in others it is horny. In the Gorgonia verrucosa it is horny, solid, fibrous, and extends from the roots to the terminations of all the branches; it is elastic, of a dark brown or black colour, is sometimes smooth and polished, and at others longitudinally striated, and is traversed by a central white pith.
The longitudinal rugæ are sometimes present, and at others absent, circumstances which do not depend much on the season of the year, but rather on some peculiarities of growth.
The axis is covered with two membranes, one proper to the fleshy bark, the other to the axis; but they are not at all times equally well marked. The membrane of the bark lies in close contact with that of the axis: this membrane is fibrous, longitudinally striated, and perforated with numerous oval openings; these, on one side, communicate with the cells of the polypes by means of the canals of the bark; on the other, with similar openings in the membrane of the axis. If this membrane be suffered to undergo partial decomposition its texture becomes separated into cellular-looking bodies, very similar to what Ellis has figured in his 'Essay on Corallines,' pl. 38, A 3, as belonging to the Gorgonia placomus. They however slightly differ, as they probably do in each species. In the Gorgonia verrucosa
