teristic feature in many of the Rugose corals. In many of these (fig. 68), the original polype throws up from its calicine disc one or more new corallites, which kill the parent. These, in turn, produce others after a similar fashion, till the entire corallum assumes

the form of an inverted pyramidal mass resting upon the original budding polype. In other Rugose corals the calicine disc gives off but a single bud, which may repeat the process indefinitely till the corallum presents the appearance of a succession of inverted cones placed one above the other.

(4) Fission. This process in the coralligenous Actinozoa is usually effected by "oral cleavage," the divisional groove commencing at the oral disc, and deepening to a greater or less extent, the proximal extremity always remaining undivided. According to Dana, in fission a new mouth is formed in the disc near the old mouth, and a new stomach is formed for the new mouth, round which the new tentacles are then developed. This, therefore, is not, strictly speaking, a subdivision into halves; since one half carries off the old mouth and stomach. More rarely, fission "is effected by the separation of small portions from the attached base of the primitive organism, whose form and structure they subsequently, by gradual development, tend to assume."

Car

The coral-structures which result from a repetition of the fissiparous process are of two principal kinds, according as they tend most to increase in a vertical or in a horizontal direction. In the first of these cases the corallum is cæspitose, or tufted, convex on its distal aspect, and resolvable into a succession of short diverging pairs of branches, each resulting from the division of a single corallite. In the second case the coral becomes lamellar. "Here the secondary corallites are united throughout their whole height, and disposed in a linear series, the entire mass presenting one continuous theca.' Both these forms of corallum "are liable to become massive by the union of several rows or tufts of corallites throughout the whole or a portion of their height. An illustration of this is afforded by the large gyrate corallum of Meandrina, over the surface of whose spheroidal mass the calicine region of the combined corallites winds in so complex a manner as at once to suggest that resemblance to the convolutions of the brain which its popular name of Brain-stone Coral has been devised to indicate" (Greene).

The Zoantharia sclerodermata are divided into the four following groups, founded upon the characters of the corallum:

1. Aporosa.-The calcareous tissue of the corallum is more or less compact and imperforate; the septa usually constituting complete solid plates, and the theca being as a rule not pierced by any apertures. Dissepiments or synapticulæ are usually present, but tabulæ are rarely developed. This section includes the most highly developed of existing corals (Turbinolida, Oculinida, Astræida, Fungida, &c.).

2. Perforata.-The calcareous tissue of the corallum is more or less

porous, loosely aggregated, spongy, or reticulate, the walls in all being perforated with more or fewer apertures. The septa are generally well developed, but they are also perforated by apertures, and may be simply trabecular. Imperfect dissepiments may be present, and in a few cases there are well-developed tabulæ ; but the visceral chamber is usually more or less completely open from top to bottom. The three families comprised in this section are the Eupsammide, the Madreporida, and the Poritida.

3. Tabulata.-The visceral chamber is divided into stories by welldeveloped tabulæ, and the septa are rudimentary or absent. This group is a merely provisional one, and its value is quite uncertain. Amongst the recent "Tabulate corals," Millepora (fig. 56) has been shown to be probably a Hydrozoön; Heliopora, as we shall see, has been proved to be an Alcyonarian, and carries with it a number of extinct forms; whilst Pocillopora has been shown to be a member of the Aporose section of the Zoantharia sclerodermata. There remain, however, a number of fossil corals, such as Favosites (fig. 66) and its allies, Chatetes and its allies, Syringopora, Halysites, Thecia, &c., which cannot at present be positively classed, and which may be temporarily retained as constituting a " Tabulate" section of the Zoantharia sclerodermata.

4. Tubulosa.—Corallum, simple or compound, the thecæ trumpet-shaped, tubular or pyriform, without tabulæ, and having the septa indicated by mere striæ on the inner surface of the wall. This is, like the Tabulata, a provisional group, and it is doubtful if it can be retained in the Zoantharia. It includes only the Paleozoic genera Aulopora and Pyrgia.

CHAPTER XIV.

ALCYONARIA.

ORDER II. ALCYONARIA.-The second great division of living Actinozoa is that of the Alcyonaria, defined by the possession of polypes with eight pinnately-fringed tentacles, the mesenteries and somatic chambers being also some multiple of four. The corallum, when present, is usually sclerobasic, or spicular; if "theca” are present, as is rarely the case, septa are wanting or rudimentary. The Alcyonaria or "Asteroid Polypes" differ numerically from the Zoantharia in having their soft parts arranged in multiples of four, instead of five or six, as in the latter, whilst the septa are not in pairs. Their tentacles, too, are pinnate, and are not simply rounded. Numerically, the Alcyonaria agree with the extinct order Rugosa; but the latter invariably possess a well-developed sclerodermic corallum, the thecæ of which exhibit either septa or tabulæ, or both combined.

With the exception of two genera (Haimeia and Hartea), both of which are possibly founded upon immature forms, the Alcyonaria are all composite, the tubular polypes being united by a cœnosarc, and their body-cavities being placed in com

munication by means of anastomosing canals, which ramify in the cœnosarc, and permit of a free circulation of nutrient fluids. The form of the colony differs greatly in different cases, but none possess the power of independent locomotion, most being rooted to foreign objects, or sunk in the mud, whilst some float freely in the sea. The polypes, in most of the essential points of their organisation, agree with those of the Zoantharia, the mouth opening into a tubular stomach, which in turn communicates freely with the body-cavity, and the stomach-sac being connected with the body-wall by means of a series of vertical membranous laminæ or "mesenteries." The mesenteries, however, are only eight in number, and are not paired, one of the tentacles corresponding with and opening into each intermesenteric chamber. A corallum may be wanting, and when present its structure varies. In some cases, lastly, it has been shown that the actinosoma normally consists of two kinds of polypes-one sexual, the other sexless and permanently rudimentary. The Alcyonaria are divided into five familiesviz., the Alcyonida, the Tubiporide, the Pennatulida, the Gorgonida, and the Helioporida.

FAMILY I. ALCYONIDE.-This family is characterised by the possession of a fixed actinosoma, which is provided with a sclerodermic corallum in the form of calcareous spicula embedded in the tissues. The spicules are mostly fusiform in shape, and are generally present both in the polypes themselves and in the connecting coenosarc; but there is no central solid axis.

Alcyonium may be taken as the type of the family, and it is well known to fishermen under the name of "Dead-men's fingers." It forms spongy-looking, orange-coloured crusts or lobate masses, which are attached to submarine objects, and are covered with little stellate apertures, through which the delicate polypes can be protruded and retracted at will. The polypes communicate with one another by an anastomosing system of aquiferous tubes, and the corallum is in the form of cruciform, calcareous spicula scattered through its substance. In the allied Sarcodictyon the actinosoma is creeping and linear.

In Xenia the colony is branched, and the polypes are nonretractile; and in Anthelia and Sympodium the actinosoma has the form of a membranous crust attached to foreign bodies. Lastly, in Sarcophyton (as shown by Moseley) the colony consists of reproductive zooids, which have generative organs and tentacles, and of sexless zoöids, which have neither of these organs, but possess a mouth and stomach-sac.

FAMILY II. TUBIPORIDE.-In the Tubiporida, or “organ

pipe corals," of which T. musica (fig. 69) is a familiar example, there is a well-developed sclerodermic corallum, with theca, but without septa. The corallum is composed of a number of bright-red, tubular, cylindrical thecæ, which are united together externally by horizontal plates or floors, which appear to be formed by periodical extensions from the mouths of the tubes. The polypes are usually bright green in colour, and possess eight tentacles each.

As shown by Prof. Perceval Wright, the tubes of Tubipora are in reality composed of fused spicules; and the polypes

Fig. 69.-A, Portion of the corallum of Tubipora musica, of the natural size, showing the tubular corallites and their connecting floors; B, Polype of the same, greatly enlarged, showing the mouth and tentacles.

when alarmed retract themselves within their tubes, the upper portions of which are composed of loose fusiform spicules, and are thus capable of withdrawal into the lower dense portion of the thecæ.

FAMILY III. PENNATULIDE. The Pennatulida, or "Seapens," are defined by their free habit, and by the possession of a sclerobasic, rod-like corallum, sometimes associated with sclerodermic spicules.

Pennatula (fig 70), or the "Cock's comb," consists of a free cœnosarc, the upper end of which is fringed on both sides with feather-like lateral pinnæ, which bear the polypes; whilst its proximal end is smooth and fleshy, and is probably sunk in the mud of the sea-bottom. This latter portion of the cœnosarc is likewise strengthened by a long, slender, styliform sclerobasis, resembling a rod in shape, whilst spicula occur also in the tentacles and ectoderm. The general colour of Pennatula is a deep reddish purple, the proximal extremity of the cœnosarc being orange-yellow. The common British

species (Pennatula phosphorea) varies from two to four inches. in length, and is found on muddy bottoms in tolerably deep

water. Its specific name is derived from the fact that it phosphoresces brilliantly when irritated.

In Virgularia (fig. 72), which, like Pennatula, occurs not uncommonly in British seas, the actinosoma is much longer and more slender than in the preceding, and the polype-bearing fringes are short. The polypes have eight tentacles. The sclerobasis is in the form of a long calcareous rod, like a knitting-needle, and part of it is usually naked. No spicula are found in the tissues of Virgularia. In the nearly-allied Pavonaria the polype-mass is quadrangular in shape.

In Veretillum (fig. 71), the upper portion of the colony is short and club-shaped, and carries the polypes all round its circumference, and the same is the case in Cophobelemnon; whilst in Renilla the polypes are unilateral, and the polypiferous coenosarc is thin and reniform.

In many of the Pennatulida, as originally shown by Kölliker,