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internally, where superiorly are the so-called cordons pelotonnes.
The cord-like fringe which is attached to the internal and free surface of the mesenteric folds, joins them close up to the pylorus, and reaches low down, where it becomes free. These fringes have been called by many names, and have had various physiological duties assigned to them. Edwards and Haime termed them the cordons pelutonnes, and they have generally been considered as part of the reproductive apparatus. But the evidence that they are
ovaries is wanting in exactitude. They have been described as being tubular, but very careful research fails to detect a canal, and they gradually become joined by a community of tissues internally with the mesentry, a faint line very structureless intervening. On the outside of the cordons are large cilia situated upon a tissue formed by great nematocyst cells, but the inside is like that of the mesentery, the inner layers of the tentacules and of the tissues generally.
The mesentric folds evidently produce within themselves ovaries or spermatic capsules, as the case may be, or both of these elements of reproduction. Hermaphroditism is however rare in the Actinozoa. Usually a considerable series of calices in a compound coral are of the same sex, and it is very probable that there are male and female compound individuals, but further researches are required on this point. The folds are inteusely ciliated on their free lateral surfaces,
and their internal structure is that of nematocyst and globular cells connected very loosely together. If there are any ova the mesenteries will be found to be swollen in an oblong form, nearly midway between the superior junction with the cordons and their lower end, and it is evident that the lax cellular tissue has some unusual histological elements within its meshes. The existence of opaque masses more or less coloured, in the tissue of the mesenteric folds, may be determined with the aid of a low magnifying power, they are the ovaries, and their structure is cellular like the rest of the fold, but some of the globular granule-bearing cells are taking on the appearance of ova, and are becoming more or less possessed of the true character of germs, according to the time at which the ovarian mass happens to be studied.
Lucaze-Duthiers in describing the generative organs of Gerardia says, that the largest ova are oval, have a coloured granular vitellus, and a colourless vesicle with an included germinal spot.
The vesicule of Purkinje often occupies the large end of the ovalshaped ovum and even comes in contact with, and lifts the vitelline membrane. There are some evidences of a micropyle at the smaller end of the membrane. It is difficult to determine without careful tearing up whether a mesenteric fold is acting as a stroma for ovaries, or for the male element. This is developed in the same position as the ovaries and ova, and occasionally it may be distinguished by the want of colour in the oblong swelling in the fold, for the ovarian masses are reddish, from the faint red tinge of the vitellus, whilst the spermatic capsules are a faint yellow. The spermatic elements are developed within capsules or large cells, which are scattered about in the inner lax cellular tissue of the mesenteric folds; they have, even when slightly developed, a very curious appearance, on account of the very pellucid character of their central mass. The capsular membrane is oval, colourless and transparent, and very homogenous; it encloses cells, granules and corpuscules, mixed up with the spermatozoa, but centrally there is the appearance of a hollow space. An oval capsule is about too of a millimètre in length, and the contents escape at the large extremity. The spermatozoa have a large refractile head and a long tail, which as is usual is very elastic, moveable, and acts as an impulsive agent to the blunt end; they resemble those of the higher animals, and are vigorous in their motions in sea-water. The ova and capsules increase in size within the mesenteric folds of the Actinides, and finally reach the perigastric cavities by rupture of the ciliated membrane of the fold, but in the Alcyonaria the ovaries and the capsules are prolonged into a fold of
the mesentery, which soon separates into a series of peduncles, which allow the male or female elements as the case may be, to float in the visceral cavity, hanging on to the mesenteric structures. When mature the pedunculated masses give way, and ova or spermatozoa are set free. The spermatozoa, after escaping from their capsules, swim freely in the water of the visceral and perigastric cavities, and rush into the surrounding sea through the mouth or the tentacular canals when these last exist. The male elements are assisted in this by the cilia of the tissues of the cavities and by their own peculiar power of movement. .
Once in the medium around the corals, the spermatozoa have to thank the usual chapter of accidents for an opportunity of being placed within the range of the ciliæ of female Actinozoa. By the currents produced, they are forced through the lips, down the stomach, and into the visceral cavity, and coming in contact with the mesenteric fold they have the opportunity of perforating its tissues, and of entering the micropyle of an ovum. Probably the water around vigorous corals is at times crowded with the spermatozoa, and vast numbers of them may be taken in at once. Moreover, the duration of the season for impregnation may be considerable, for considering that every tentacule represents a mesenteric fold, and each of these contains hundreds of ova, and the myriads of tentaculiferous polypes there are in a good sized compound individual, it is not probable that all the ova must of necessity be affected by the spermatozoa at one particular time, so as to render fertility inevitable. Nevertheless, there must be an enormous number of ova never fertilized, and a corresponding bulk of unused spermatozoa. How the blunt-headed zooid manages to get through the ciliated tissue of the mesentric fold, and then to come in contact with and penetrate the micorpyle of an ovum has not yet been determined, but it is evident that a great current sets in down the mouth into the cavity lined with the mesenteric folds, and then occasionally outwards through the tentacular canals. Such a current would bring the zooids within reach of the ova if any of them were large enough to distend the fold. Less difficulty must occur in the impregnation of Alcyonarians whose ova are simply covered with a delicate membrane, and which are floating in the visceral cavity being held by their peduncules. In this case the contact must be easy and inevitable. Probably soon after impregnation these pendulous ova become ciliated and burst their containing membrane.
There must, however, be a different process in the Zoantharia, whose ova are surrounded by a stroma of cells.
The impregnated ova in these, escape by rupture of the surrounding cellular tissue. Having previously become very ciliated they move freely about in the visceral and perivisceral cavities. Either they pass out of the mouth of the parent by the aid of their ciliæ which enable them to move in the sea as long as the first stage of their life lasts, or this stage is passed within the visceral cavities, and the perfect Actinozoa emerge ready to become fixed to their permanent position.
There is something very remarkable in these ciliated ova, for they constitute a larval stage : they are more than ova, for these have no cilia when within the mesenteric folds. A certain development has taken place to fit them for locomotion, but they do not appear to assimilate, or even to receive food. In the Cerianthes, the larva after a while becomes thin and conical at one end, but a concavity is noticed at the other, previously to a small opening being formed which permits some granules to escape. This is the future mouth. Four little projections arise around the mouth, the earliest of the tentacules; and then two folds are noticed, which are the rudimentary lips. At the expiration of a longer or shorter period, the tentacular appendages become contractile, and surround a dilatable mouth; the whole of the surface of the larva becomes elongate and highly ciliated, and the Cerianth swims head downwards, like one of the Medusæ. It finally settles down, is more or less covered with sand, and developes a multitude of tentacules, and around itself the remarkable sheath which characterises the genus. The Actinidæ soon develope six tentacules instead of four, and their base becomes flattened, so that they readily attach themselves. All the Alcyonaria produce eight tentacules, and no more; so that as the polypes increase in size, there is no increase in the number of the mesenteric folds. There is, moreover, a distinction between the mesenteric folds of the Alcyonaria and those of the Actinides ; for they are intimately joined in pairs in the first, and open for the further development of sub-tentacular growth in the last. To conclude this short resumé of the reproduction of the Actinozoa, it may be noticed that Cerianthus is a genus which has hermaphrodite polypes, the ova and the spermatic capsules being found in the same mesenteric fold.
The development of the sclerenchyma is very difficult of observation in the Madreporaria, but it has been very well followed in the Gorgonides and Antipatharia. Some simple Madreporaria, and a great many of the aggregated forms, have a dense lamellary tissue, or a fine and semi-transparent layer, which acts like a sheath
to the outside of the lower part of the coral. It covers over the outside wall and the costæ up to a certain height, reaching even to the calicular margin in some genera. It can be broken off, and the tissues beneath are then shown in all their perfection. This epitheca, as it is termed, is rarely ornamented; is abundant or rudimentary, as the case may be ; and even, in some fossil species, forms the outside wall, replacing the true wall completely; it is often produced into ridges, spines, and radicules. Secreted by a special tissue, it is present in every species at that stage when the larva attaches itself to a foreign substance. It forms an agglomeration of granules at the base of the larva, and fixes it. The growth subsequent to this depends upon the species; but it does not go on 'until the sclerenchymatous nodules or granules are deposited within the layers of the innermost tissues in sufficient quantity to form the base of the wall and the first traces of septa. When the wall, septa, and costæ, with their accessory dissepiments, attain a certain development, the epitheca grows again, but it always remains connected with the base. The hard tissues, with their surrounding soft parts, are covered by it, and it loses its own secreting tissue very soon inferiorly. It is the secretion of the hard parts (thus covered) by the deep tissues of the Madreporarian polypes that gains for them the name of “ sclerodermic” Zoantharia.
In the Gorgonides and Antipatharia, the epitheca is the sole hard part. There are no walls, septa, or costæ. As soon as the polypė fixes itself, after the end of the larval stage, a basal epitheca, often red or black in colour, is noticed at its base; the soft parts curve over it like the turf over a bill; and, as growth proceeds, the elevation increases by the development of successive layers on top of the basal epitheca. The polypous openings in the sarcode which covers the greater part of the surface of the elevation, are independent of the hard tissue, and water canals radiate over and cover it. The elevation, which has really become an axis, remains smooth, channelled, serrate, or spiculate, branches here and there, and solidifies more and more. But it is really a continuation of the basal epitheca, and bears the same relation to the soft tissues of the Actinozoon as a finger does to a glove. It is not secreted by the tissues which line the cavities of the polypes, but by the original external basal membrane. Hence these Actinozoa are
are called “ sclerobasic.”
The nutrition of the sclerenchyma and of the soft tissues must now be considered.
The water system of the coral polypes is very interesting to