JOURNAL

OF THE

ROYAL MICROSCOPICAL SOCIETY.

MAY, 1878.

I.-On a New Coral, Stylaster stellulatus; and Note on
Tubipora musica.

By CHARLES STEWART, F.L.S., Hon. Sec. R.M.S.
(Read before the ROYAL MICROSCOPICAL SOCIETY, March 6, 1878.)

PLATE III.

THE interesting papers by Mr. H. N. Moseley on the Milleporida and Stylasteridæ,* confirming the view long held by many naturalists, that the former really belong to the Hydrozoa, and showing that the latter (Stylasteridae) should be referred to the same class, have given special interest to a group of corals long remarkable for the beautiful permanent colour which most of them present. As a probably new species of Stylaster has recently come under my notice, I have thought that a few remarks on it might be of interest to this Society.

I am indebted for the specimen to the kindness of Mr. H. P. Potter, who accompanied Mr. Brassey in his recent voyage round the world. It was given to him at Tahiti, with the statement that it was extremely rare, and only found at one small island in the neighbourhood.

The corallum is of a bright rose colour, especially in the younger branches, the older parts being often more pale. The

DESCRIPTION OF PLATE III.

FIG. 1.-Lateral branch of S. stellulatus, showing crowded calicles, some undergoing division. X 25 diam.

2.-Fragment of branch, showing ampullæ. × 25 diam.

3.-Orifice of calicle. x 40 diam.

4.-Vertical section of calicle, showing canals and style. × 40 diam.
5.-Fragment of Tubipora musica, the thecæ have been opened in places to

show included tube.

× 3 diam.

6. Fragment of tube. x 83 diam.

branches are usually quite cylindrical, though occasionally flattened at their tips; the general appearance being much like that of S. sanguineus, but it has a bluer rose tint, and is at once distinguished by the minute size of its calicles (of an inch) which are usually uniformly and densely scattered over the branches, a few of which only show them to be more abundant at the contiguous edges. Each apparent calicle really consists, as has been pointed out in the papers already alluded to, of a central cupshaped calyx (which in life bears the alimentary zooid), having an opening in its floor from which a large tube passes towards the interior of the corallum: running throughout the whole length of the tube is a minutely spined style-like columella whose point may be seen in the centre of the hole at the bottom of the calyx. Around the calyx and attached to its outer surface is a series of from ten to fourteen vertical plates, which, although they so closely resemble the septa of an Actinozoan corallum, are really only the remains of the coenenchyma which separates the individual members of a circle of tentacular zooids that surrounds the central alimentary one. The outer border of these plates is attached to the surrounding cœnenchyma, which is often raised around them so as to resemble the theca of an ordinary coral. The edge of this false theca is sometimes more raised on the proximal side (nearest fixed end of corallum), at other times on opposite sides corresponding with the plane of the branches, but is absent or slightly developed on the larger branches where the axis of the group of zooids is at a right angle to the surface. At some depth between each of the septa may be seen a small, rounded, brightly glittering, and nearly colourless sphærule attached to the theca; much smaller, but otherwise similar ones, stud the larger canals, and are especially evident around the opening through which the style projects. The general substance of the coenenchyma, although exceedingly hard, is permeated by numerous small and branched intercommunicating canals which open into the main canals of the alimentary and tentacular zooids, and also upon the general surface, which is somewhat raised between them. They appear as white lines on the section surface, as their interior appears to be covered with an amorphous opaque deposit.

Besides the calicles which give the chief beauty to the coral, some of the branches show small rounded or conical elevations (ampullæ) of the surface, mostly situated on the non-contiguous sides of the branches, the apices of the elevations having one or more small perforations. These have been shown by Mr. Moseley to be the chambers in which are contained the adelocodonic reproductive organs. In some cases the elevation is not marked, although the hole is present, which then sometimes has a white spine-like process by its side.

The number of the calicles appears to be increased by fission. In the coral the first indication of this is the appearance of the points of two styles close together. A bridge stretches between the points of the styles. The calicle increasing in size first becomes oval, with an increase in the number of septa; further constriction then completes the separation. I have sometimes seen obscure indications as if at times the calicles might occasionally arise by the simultaneous budding of tentacular and alimentary zooids from the surface of the coenosarc. The apparent division of the calicles is perhaps really a case of fusion; this is favoured by the fact that the apices of the styles are directed towards one another. But the normal number (thirteen) of the septa is the same in a calicle with two styles, and increases with their separation, until, when nearly complete, they are usually twenty-six. Such an abortion of zooids following fusion does not seem probable.

The chief points in which the corallum of this genus differs from that of the Actinozoan corallum, which it in appearance so closely resembles, are

That it is secreted by the ectoderm.

That it is permeated by anastomosing canals, which are traversed by tubular prolongations of the body wall corresponding either with the hydrocaulus or hydrorhiza of other hydrozoa (reminding one of the hydrorhiza of Antennularia).

That the calicles are groups of chambers, the central one for the alimentary, the marginal ones for the tentacular zooids.

That the septa are the remains of the cœnenchyma between the tentacular zooids.

And that the theca is but the elevation of the cœnenchyma around the group of zooids.

Although many descriptions of the corallum of Tubipora musica have been given, I have not seen a notice of a peculiar feature which I have found present in nearly all specimens examined, but which is particularly marked in one in my own possession. This feature consists in the presence of a second tube averaging about one-third the diameter of the including theca. It is very delicate, and of a pale rose colour; its thin perforated walls appear to be composed of numerous branched flattened spicules having a fibrous texture. The tube is generally connected with the theca at the points where the plates of connecting conenchyma are found, either by spreading out here into a funnel-like end or by tubular branches.

In the absence of soft parts, one can only speculate on their real meaning. It seems possible that by them a communication might be kept up between the body cavities of the living zooids on the surface of the corallum and the canals in the tables of cœnenchyma, from which budding often takes place. The remains of the