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appears to close it below; this is the columella, but it has no connection with the disc. The mouth leads to a short tubular canal, and at the lip, which is marked with radiating ridges, the external tissues of the disc dip down, and line this canal—the stomach. The stomach passes downwards for a short distance, and forms a constriction, the pylorus, which leads to the great gastric cavity, in whose centre is seen the top of the columella.
The radiating lines or furrows seen on the labial opening of the stomach be traced like radii over the disc towards the external margin, and, moreover, they pass downwards on the sides of the stomach forming its vertical folds. The stomach, thus marked, is short, very extensible, and is free inferiorly at the pyloric end. Internally it is washed by the water passing down through the mouth to the gastric cavity by the pylorus. Superiorly it is continuous with the tentaculiferous disc through the lips, and externally it is washed by the water contained in the cavity already noticed as being bounded above by the lower plane of the disc, and below by the septa and thej depths of the calice. The tentacules open inferiorly into this cavity, which is, moreover, partitioned off by some structures, which are attached above to the under part of the disc along the line of the radii from the lip, and internally to the outside of the stomach on a line with its folds. These structures are double folds of membrane-mesenteric folds-and the tentacular canals open into them or between them. The attachment of the folds to the lower surface of the disc is the longest, and that to the stomach is very short, for it ends at the pyloric extremity, and then the mesenteries are passed downwards free. The septa fit in between the radiating folds, and have a definite numerical relation to them.
When the tentacules are fully expanded, the most external fall over the margin of the calice, and the others crowd within them, their bulbous ends being constantly in motion. They hide the subjacent hard parts, and present different colours, according to the light and the definite colouring cells.
The tentacules have a bulb, which is perforated and usually not ciliated, and the rest of their external surface is ornamented with projecting scutiform processes, and is covered with cilia. The ciliated condition of the lower part of the external surface of the tentacules is seen to be repeated on the surface of the disc and on the labial projection; but its absence from the terminal bulb is compensated by the peculiar structure of its tissue.
Jules Haime, in his careful study of the minute anatomy of
Cladocora ccespitosa, notices the three layers of tissue which characterize the tentacules, and the rest of the soft parts. The external envelope is quite transparent, and is composed principally of nematocysts of three dimensions, those of medium size being the commonest; also of very simple cells, either irregular in shape, or oblong, or uniform; and of small rounded and transparent globules, which form the innermost layer. The middle tissue is formed by muscular fibres, which are very sparsely distributed; and the internal tissue is formed by a layer of transparent cells tolerably adherent to each other, and by a layer of colour-bearing globules which are spherical, or slightly oval in shape. The nematocysts which form the most important part of the integument of the tentacules, and which are also found in positions where it is difficult to account for their presence as weapons of offence, are slender, elongate, and generally cylindrical cells, smaller at one end, and they contain a thread regularly rolled up as a spiral. Near the large end of the cell the spiral ends in a straight portion, which is also central. The large end, moreover, gives exit to the nematocyst thread. The tentacular bulb is nearly composed of these cells mixed up with others, which have the thread rolled up in spirals, but whose cellwall is often wanting. The colour-bearing cells of the innermost layer contain granules of irregular shape, and the distribution of these cells is remarkable, for they exist within the gastric membranes as well as where they can produce an effect upon the light. This inner tissue, besides producing the colours of the soft parts, secretes the calcareous skeleton, and appears to have a power of absorbing portions of it during the growth of the coral. In examining the hard parts, it must always be remembered that they were deposited through the intervention of a tissue which covered them on all sides, and permeated even the densest portions. Modifications of the external and internal tissues, the middle or muscular being invisible in many parts, constitute the stomach, the mesenteric folds, and the ovarian structures, and produce the buds observed in some genera. All the internal hard parts, such as the septa and the columella, and the dense texture connecting them, being lined with the soft tissues which join those of the disc at the margin of the calice, it follows that the gastric and perigastric cavities, thus enclosed, are everywhere bounded by a continuous layer of soft tissue, which absorbs nourishment, and is aërated by the influx of pure sea-water through the mouth, and by its discharge both by the mouth and the tentacular canals.
The Plate represents the Caryophyllia borealis (Fleming.) The
central figures are those of the skeletons of the coral attached to a Ditrupa, and of a living specimen with its tentacules expanded. These are the size of life. A magnified view of the tentacules is shown. The upper and lower figures are magnified views of the calicular surface of the coral, the one being from a living form and the other from the dead. Mr. Peach was good enough to send me the drawings of which these are copies.
THE ANNELIDAN WORMS, OR ANNELIDES (ANNELIDA).
BY W. BAIRD, M.D., F.R.S., F.L.S., ETC.
(With two Plates.)
The worms, of which this article is the subject, are those which Cuvier, and many others since his time, denominated “Red-blooded Worms,” or Annelides.
Worms, in a popular sense, are little, if at all, desirable creatures to contemplate ; they are, in fact, “caviare” to the multitude, and are to thousands mere objects of disgust and annoyance. Poets and romancers have agreed to render them vile. The “ laidly or loathly” worm is an expression of frequent occurrence, and in the “Mysteries,” Satan is described as a "worm with an aungelys face.” Naturalists, again, have generally described them as a degraded ” section of the animal kingdom.
I hope, however, before this paper is concluded, to demonstrate that at all events the Annelidan Worms are well worthy of our attention and even admiration.
The great Linnæus, when he first established his arrangement of the animal creation in the "Systema Naturæ," adopted for one of his great classes that of the worms, or Vermes. Our great teacher embraced in this class a most heterogeneous assemblage of the lower forms of creation; the intestinal worms, the shell-less, and the shelled Mollusca, the corals and zoophytes, including the Foraminifera, the sponges, etc., were all embraced in this great class—were all ranged together under the general name of worms, or Vermes.
Linnæus was certainly not very happy in this division of the animal kingdom. Little was known, in his time, of the animals belonging to the lower orders of creation. Some of the worms now arranged in the class of Annelides, such as the Lumbricus, or earth
worm, and the Hirudo, or leech, he placed in his group of intestinal worms (Intestina); others, such as the Terebella, or tubicolous Annelides, the Aphrodita, or sea-mouse, and the Nereides, amongst the shell-less molluscs (Mollusca); and others again, such as the Serpula and Sabella, both tubicolous Annelides, he placed among his shelled molluscs (Testacea).
The natural relations and anatomical characters of many of the Annelidan animals, arranged in this class Vermes, were made subjects of remark and observation by Pallas, Muller, and Otho Fabricius, who immediately succeeded Linnæus, but systematic writers continued for a length of time after the publication of the “Systema Naturæ,” to arrange the animal creation as Linnæus had done, and left the Annelides amongst others, as he had disposed them.
Cuvier, taking advantage of what had been done by his predecessors, such as those mentioned above, and seeing clearly the immense advantage of taking anatomy and physiology as bases for a methodical distribution and classification of the lower animals, proposed in his “Règne Animal,” great changes in their arrangement. He instituted a great division, which he denominated Articulata, jointed or articulated animals, and in this he placed as a class apart from all others, that of the Annelides, which he called redblooded worms. Led away by the value he assigned to this class in general, of many of them possessing a red coloured circulating fluid, or red blood, he placed them at the very head of this great division. Cuvier, however, was better acquainted with the higher classes of the animal kingdom than the lower, and it need not surprise us to find that since his time various improvements and changes have taken place in this portion of his system, more especially with regard to the claims of the nervous system as a basis of classification.
We are particularly indebted to the writings and labours of MM. Audouin and Milne Edwards, for the first breaking up of Cuvier's arrangement of the articulated animals. His great group “Articulata” has been split up into several others, and fresh subdivisions have been formed as respects the class Annelida. M. Quatrefages has still more lately made this class the subject of particular study, and his investigations into the structure and physiology of the different creatures placed in it by naturalists, have been of the greatest importance.
We cannot enter here into the various changes of classification made since Cuvier's time, but we may simply state that the large class Annelida, as now acknowledged, consists of animals which may
be known by their having, in addition to a segmented body and a complete circulation of blood in closed vessels, a nervous system constructed in conformity with the articulated type. This system is characterized essentially by the presence of a ganglion on the dorsal aspect of the esophagus, and hence called the “cephalic,” or
præ-esophageal ;” and another on the ventral surface of the esophagus, known as the post-esophageal.
These two ganglia are united by means of intermediate cords which descend on each side of the esophagus, so as to embrace this tube in the inclosed span, thus forming the esophageal ring, through which the esophagus passes. (See Plate I., Figs. 1, 2, 3).
In accordance with this view, naturalists now, in addition to the Annelida, as contained in the systems of Cuvier, Milne Edwards, and others, admit into this class the siphunculoid worms, or Gephyrea, whilst the Turbellaria, and Nemertine worms, which have frequently been included amongst the Annelides, but which have a less highly developed nervous system, are excluded.
Having thus explained the proper position and extent of the Class of Annelides in the animal kingdom, we must now say a few words about their divisions into Orders.
Cuvier divides them into three Orders, as follows :
I. TUBICOLA, or tubicolous worms, the “ Pinceaux de Mer," or sea-pencils of the French writers. This order contains the Serpulæ, the Sabellæ, the Terebellæ, etc., which all live in tubes formed by themselves for a permanent residence.
II. DORSIBRANCHIATA, or Annelides which have their breathing apparatus or gills (branchiæ) placed equally along the whole body. This order contains the sand-worms (Arenicolæ), the Amphinoma and Euniceæ, the Nereides (Nereis), the Glyceræ, the sea-mice or Aphroditidæ, the scaled-worms (Lepidonoti), etc.
III. ABRANCHIATA, or worms which have no apparent external organs of respiration (branchiæ), such as the earth-worm (Lumbricus), the Naides (Nais), the leech (Hirudo), etc.
Grube, a distinguished German helminthologist, in his “ Familien der Anneliden,” divides the Annelides into five Orders
I. Appendiculata polychæta.
The 1st Order, Appendiculata polychæta, he divides into two great groups, Rapacia, or animal-killers, and Limivora, or mud.