Page:Encyclopædia Britannica, Ninth Edition, v. 6.djvu/415

Rh CORALS 385 shown by Dr &quot;Wright, being composed of fusiform warty spicules which are loose, and thus allow this part to be pulled iuto the lower dense portion of the theca. The mouth is placed between the Fia. 12. Tubiporidse. A, Portion of the corallnm of Tubipora musica, of the natural size, showing the tubular eorallites and the exothecal tabular. B, Polype of the same, gieatly enlarged, showing the mouth and tentacles. bases of the tentacles, with a slightly elevated lip, and leads into a small stomach-sac. There are eight mesenteries, within which the reproductive organs are contained. The exothecal expansions, by which the tubes are united, appear to be produced periodically as horizontal extensions from the mouths of the tubes. Fam. III. PENNATULID^E. The &quot; Sea-pens &quot; and &quot;Sea-rods are compound Alcyonaria, but instead of being rooted to some foreign object, they possess a fleshy, usually columnar or rod-like base, which is non-polypiferous, and is plunged in the sand and mud of the sea-bottom. The upper portion of the colony carries the polypes, and varies much in shape. Sometimes the polypes are borne on long lateral pinnae, which give the upper portion of the actinosoma a feather-like appearance ( Pcnnatida) ; whilst at other times there are similar but much shorter pinnae ( Virgularia). In VcretiUum the upper portion ol the colony is short and club- shaped, and carries the polypes all around its circumference, and the same is the case in Cophobel- emnon. In Pavonaria the polypes are non-retractile, and are disposed on one side of the slender acti nosoma ; whilst in Renilla the polypes are also unilateral, but tho polypiferous surface is thin and reniforrn. In Umbellularia, the polypes are carried in a cluster at the top of the actinosoma. The corallum in the Pennatulidce is usually two-fold, consisting on the one hand of a slender, styliform, horny, or calcareous axis (sclero- basis) concealed within the coeno- Barc, which it serves to support, and, on the other hand, of Email calcareous spicules scattered amongst the soft tissues. In some cases the sclerobasis is rudi mentary. The Pennatulidce often possess the power of phosnhores- Colony of Vtretillum cynomorium. reiipp in a hicrh dp^rpp anrl thpr linn., of the natural size, with the ma mgn uegree, ana tney polypes protruded, possess the same system of cceno- sarcal canals as is characteristic of the Alcyonaria generally. The polypes have eight pinnately-fringed tentacles, and eight mesenteric folds. In many cases, as originally shown by Kolliker, the colony consists of two classes of zooids, the one composed of sexually mature polypes, the other, more numerous, composed of sexless polypes, in which the tentacles are not developed. Fam. IV. GORGONID.E. The &quot;Sea-shrubs&quot; possess a more or less branched ccenosarc, which is permanently rooted to some foreign object, and is provided with a grooved or sulcate branched sclerobasis, with which are associated true tissue-secretions in the form of variously shaped sclerodermic spicules (&quot; sclerites&quot;). As regards their soft parts, the Oorgonidce do not differ from the other Alcyonaria, the polypes possessing eight fringed tentacles, with eight mesenteries, united by a canal-system, which ramifies through a fleshy ccenosarc. The coenosarc, however, is always closely applied to, and supported by, a more or less branched sclero basis, over which it forms a thin fleshy expansion (&quot; cortex &quot;), and the polypes are capable of complete retraction within the coenosarc. The soft tissues are also abundantly supplied with true sclerodermic Fin. 13. Pennatulidae. secretions, In the form of calcareous spicules of very various shapes, and often of very brilliant colours, which are in many instances so characteristic in their form that they can be employed as a ground of generic distinction. The spicules ( &quot;sclerites&quot;) are usually buried in the soft tissues, but they may project beyond the surface of tho coenosarc in such numbers as to render the integument rough and scoriaceous ( Muricea). The sclerobasis varies greatly both in tex ture and form. Sometimes it resembles that of the Antipathidce in being corneous and unjointed, but its surface is always striate or grooved, whereas in the &quot; Black Corals &quot; it is smooth or echinulate. Its form is usually more or less branched, dendroid, or minutely arborescent (as in Primnoa, Muricea, Cforgonia, Leptogorgia, &c.), or it may be in the shape of a regularly reticulate flabelliform expan sion (Rhipidogorgia). In the genus Isis the sclerobasis is branched and articulated, composed of alternating calcareous and horny joints, and having the new branches produced from the calcareous nodes. In Melithcea and Mopsea, again, the corallum is likewise branched and articulated ; but the joints are alternately hard and soft ; the hard joints being composed of fused calcareous spicules, and the flexible joints of horny matter intermixed with calcareous spicules and connective tissue, whilst the new branches are deve loped from the corneous segments. Lastly, in Eed Coral (Coral- Hum) the sclerobasis is unjointed, more or less branched, and densely calcareous. It is of a red or pink colour, and finely grooved upon Its surface ; and it is really composed of fused spicules, and thus differs very materially from the true sclerodermic corallum. The calcareous axis is covered with a bright red ccenosar- FIG. 14. Red Coral (Corallium rubrum), of the natural size, and a portion enlarged. cal crust or cortex, which is studded by the apertures for the polypes. The polypes are milk-white in colour, with eight pinnately- fringed tentacles, and completely retractile within the fleshy bark. The polypes are further placed in direct communication by means of anastomozing canals channelled out of the ccenosarc and filled with a nutrient fluid. It has been shown by Lacaze-Duthiers that the colonies of Corallium are sometimes composed of male polypes, sometimes of female, or occasionally all the polypes of some branches of a colony may be of one sex, and all tire polypes of other branches of the opposite sex, whilst in some instances polypes occur which are hermaphrodite and combine in themselves the organs of both sexes. Fam. V. HELIOPORHWE. An examination of the living Heliopora in its fresh state has recently induced Mr Mosely to found this family for the reception of the existing genus Heliopora and a number of extinct forms previously placed amongst the Tabulata. In Heliopora there exists a well-developed sclerodermic corallum, of a composite nature, and composed of corallites united by ccenen- chyma. The corallites are tubular, crossed regularly by well-de veloped tabulae, and having their walls folded in such a manner as to give rise to a variable number (generally twelve 1 ! of septal lamina?. The ccenenchyma is composed of slender tubes, of smaller size than the true corallites, and packed closely side by side. The ccenen- chymal tubuli are destitute of septa, but, like the corallites, are crossed by regular transverse tabula. The sclerenchyma is not com posed of fused spicules, as in Corallium and Tubipora, but of fibro- crystalline calcareous tissue, as in the Zoantharia sclerodermata. The soft parts occupy only the parts of the corallum above the uppermost tabulae, and therefore only a surface-layer of the colony is actually alive. The polypes are, completely retractile, with pinnately- fringed tentacles, which are introverted in retraction. There are also eight lobed mesenteries, but these in no way correspond with the VI. 49