Corallium rubrum.

Fig. 29. Corallium rubrum.

(150). Upon making a transverse section of one of these polyparies (fig. 30, a), the solid axis is distinctly seen to be made up of layers arranged in a somewhat undulating manner around the centre, and successively deposited by the living cortex: the growth of the stem, in the harder species at least, is very slow, and several years are necessary to its maturity, - a circumstance which has rendered it needful to impose strict laws forbidding the Mediterranean coral-fishers to disturb too frequently the same localities, which are only visited at stated periods.

(151). The deposition of solid matter in the soft bodies of these polyps is not confined to the production of the central stem, but in many even of the Keratophyta* cretaceous particles are extensively diffused through the cortex, which not unfrequently is likewise gorgeously coloured by secretions of different hues. In the Gorgoniae, a section of one of which (Gorgonia verrucosa) is represented in fig. 30, a, the earthy matter in the crust is so abundant, that even when dried it will retain in some measure its natural form, and exhibit the tints peculiar to the species.

A, transverse section of Gorgonia verrucosa.

Fig. 30. A, transverse section of Gorgonia verrucosa.

B, longitudinal section of Isis hippuris, exhibiting the skeleton and fleshy crust.

* An old name for polyps with a horny axis (

Horn.

Horn.

A stem), as distinguishing them from the stony polyps   Lithophyta.

A stem), as distinguishing them from the stony polyps - Lithophyta.

A stone.

A stone.

147 Corallidae 43

(152). The structure of the individual polyps of the Corallidae resembles that of one of the polyps of the Alcyonidae already described; and the prey obtained by each goes to the support of the general mass. Their reproduction is undoubtedly from germs developed in internal filamentary ovaria, which escape either through the mouth, as in Alcyonium, or else, as Cavolini* supposed, through apertures placed between the origins of the tentacles.

(153). Pennatulidae

This family belongs likewise to the division of cortical polyps, and agrees with the two last in most points, the principal distinction consisting in the character of the internal axis which supports the body. In some species this part is reduced to a ligamentous mass, interspersed with calcareous granules; but in the most typical forms the skeleton consists of several pieces, capable of moving upon each other. The whole animal in such cases resembles a feather, the stem supporting lateral branches, upon which the polyps are arranged. From the circumstance of these compound animals being unattached to any foreign support, they have been supposed to be capable of swimming at large in the sea, by the voluntary movements of their articulated branches - a fact strongly contested by many modern zoologists; but as we can say nothing from our own observation upon this subject, we must leave the question open to future investigation. Many species are eminently phosphoric.

Figure of Pennatula.

Fig. 31. Figure of Pennatula.

(154). Tubiporidae

We have now to speak of a class of polyps very different in their construction from those which have been described. Instead of incrusting an internal solid skeleton, the Tubiporida) are enclosed in a calcareous or coriaceous sheath or tube, from the orifice of which the polyp is protruded when in search of prey: these are named by authors Vaginated Polyps.

* Cavolini (Filippo), Memorie per servire alla storia dei Polipi marini. 4to. Naples, 1785.

(155). The Tubipora musica (fig. 32, a) is the species which has been most carefully studied; and the details connected with its organization will be found of the highest importance, as affording a clue to the investigation of other forms, to be mentioned hereafter. The Tubiporae live in society, but do not appear to be organically united as the compound polyps are. A group of these animals presents several stages of tubes, placed one above another (fig. 32, a): the tubes are generally straight, and nearly parallel to each other, but appear slightly to diverge as radiating from a common centre; they are separated by considerable intervals, and reciprocally support each other by horizontal laminae of the same substance as the tubes themselves, which unite them. From each tube a polyp is protruded, of a brilliant grass-green colour, sometimes of a lilac or rose tint, the mouth being surrounded by eight tentacles, which are furnished along their edges with two or three rows of minute fleshy papillae.

Tubipora musica. a, a portion exhibiting several stages of tubes; b, an isolated tube; c, polyp expanded.

Fig. 32. Tubipora musica. a, a portion exhibiting several stages of tubes; b, an isolated tube; c, polyp expanded.

(156). The visceral cavity is long, tubular, and contains eight fleshy lamellae (fig. 33,1, e.) These lamellae aid, by their muscles, both in the contraction and expansion of the polyp. The stomach is very short compared with the whole length of the visceral cavity, and, as in the Alcyonium figured above, is connected with the sides of the cavity by the visceral lamellae.

Six of these lamellae, in a specimen examined by Dana, were spermatic, being bordered below by a white convoluted cord, while the other two gave origin to large clusters of milk-white ovules, which occupied nearly the whole diameter of the cavity. These ovules were of various sizes, and spherical in shape, or nearly so. Some observers have found all the lamellae bordered with white filaments; and others describe them as all bearing clusters of ovules. In these instances it would seem that the sexes are distinct, in one case the animal being male, in the other female. The ovules have been seen to escape by the mouth; and this therefore appears to be the general mode in all the Actinoid polyps.