Natural History: Or, Second Division of "The English Encyclopedia"

ovaries, and five from the stomach, which, before joining it, unite into two. The vessels described seem to constitute the venous system, and Tiedemann further supposes that the cæcal and gastric veins convey the chyle or nutritious part of the food from the alimentary organs. The circular vein opens into a vertical canal, which descends along the prominent angle between the two rays, inclosed in the same membranous sheath with the sand-canal, and terminates in an inferior circular vessel. The descending canal is dilated in the middle; its comparatively thick brown-coloured parietes are smooth externally, but reticulated on the inside, and composed of interlaced fibres, which Tiedemann found to possess muscular irritability. He accordingly considers this canal as the heart. The inferior circular vessel (which must not be confounded with the circular canal connected with the feet) surrounds the mouth on the outside or inferior surface; it sends out five branches, which pass into the interior of the body, and are distributed to the stomach, cæca, and ovaries. Tiedemann regards these branches, with the circular vessel from which they proceed, as arteries, and he thinks it probable that their minute ramifications open into the radicles of the veins, though from their delicacy he has not been able to ascertain the fact by injection. Tiedemann's view of the function of the respective vessels is derived solely from a consideration of their anatomical disposition; and while in the same way it may be inferred that the blood circulates in a direction conformable with this view, it must nevertheless be kept in mind that no direct physiological proof of such a course of the blood has been yet obtained. Besides the vessels described, Tiedemann found yet another circular vessel surrounding the mouth on the under surface, and placed more superficially than the last mentioned; it is of an orange colour, and sends a branch along each of the rays in the groove which is on the middle of their inferior surface. He could trace no connection between this vessel or its branches and the rest of the vascular system, and he professes himself at a loss to conjecture what may be its function.

According to Delle Chiaje, the circular vessel into which the canals of the feet open receives also the veins from the upper surface of the cæca and stomach. The same vessel, which he names the venous sinus, gives out-1, twenty short dental arteries; 2, the mesaraics to the under surface of the cæca; 3, five vertebral arteries which open into the vesicles of the feet; 4, the radial to the under part of each ray; 5, the dorsal arteries to the upper part of the ray, which extend their ramifications to the external surface of the body." (Cyclopædia of Anatomy and Physiology.')

Professor Owen, in his Preface to the third volume of the 'Descriptive and Illustrated Catalogue of the Physiological Series of Comparative Anatomy contained in the Museum of the Royal College of Surgeons in London,' remarks, that when the nervous system begins to be distinctly eliminated in the form of fibres, it is accompanied by a distinct development of the muscular system; and the digestive canal is provided with a proper contractile tunic, and floats freely in an abdominal cavity. He observes that the nervous fibres in the classes of animals in which they are first discernible proceed from a ganglion or ganglions in the neighbourhood of the mouth, and extend in a radiated or longitudinal direction according to the form of the body, but are not afterwards brought into communication by ganglionic masses. "The Echinoderms, as the Star-Fish and Sea-Urchins," writes the Professor, "first present these conditions of the nervous, muscular, and digestive systems. A very gradual transition from the radiated to the elongated form is traceable from this class through the Holothuric and Sipunculi to the cavitary Entozoa or Cælelmintha (intestinal worms having an abdominal cavity), and thence to the Epizoa and Rotifera, which make a near approach to the annulose division of the animal kingdom; but at the same time do not possess that structure of the nervous system which is its true characteristic. The four classes of animals, thus distinguished by a common character of the nervous system from the Acrita on the one hand, and the Articulata on the other, constitute a second division of the animal kingdom, which may be termed Protoneura."

The preparation No. 1292 A, in the series illustrative of the nervous system of the Nematoneura is a Star-Fish (Asterias papposa, Lam.) with the membrane removed from the oral surface of the central disc, to show the simple nervous chord surrounding the mouth and distributing filaments to each ray. These filaments run in the interspace of the tubular feet, extending from between the spines which protect the ambulacral grooves. (Catalogue.')

Tiedemann, who discovered the nervous system in these animals, describes it in Asterias aurantiaca as composed of a delicate white chord surrounding the mouth, in form of a ring immediately on the external side of the circular vessel into which the heart opens, and of filaments arising and diverging from the annular chord opposite to the rays-three filaments for each ray-one running along the under surface in the median line, and appearing to send small branches to the feet; the other two, shorter, passing between the first and second segment of the ray into the interior of the body, and probably distributed over the stomach. No ganglia were discovered by Tiedemann, but minute ganglia have been described by others as existing at the points whence the diverging filaments spring. (Grant's 'Comp. Anat.')

All of course agree in assigning the sense of touch to the StarFishes, but many would confine their endowment to that sense. Professor Ehrenberg however, who is a keen and accurate observer, is disposed to think that some of them at least are gifted with visual organs under the form of a single red speck at the termination of each ray. These specks had been long noticed, but without any determinate conjecture as to their use in the animal economy, till he, struck by their outward resemblance to the eyes of the Entomostraca and Infu soria, thought that they might be organs of sight, and he traced the long nerve of the ray up to the extremity, where it enlarges into a sort of ganglion connected with the red speck.

Professor Rymer Jones, after noticing the nervous system of these animals, thus expresses his dissent from Professor Ehrenberg's views: "Such an arrangement can only be looked upon as serving to associate the movements performed by the various parts of the animal, for no portion of these simple nervous threads can be regarded as being peculiarly the seat of sensation or perception. But this inference is not merely deducible from an inspection of the anatomical character of the nerves: it is based upon actual experiment. We have frequently, when examining these animals in a living state—that is, when, with their feet duly developed, they were crawling upon the sides of the vessel in which they were confined-cut off with scissors successive portions of the body so as to expose the visceral cavity; but so far from the rest of the animal appearing to be conscious of the mutilation, not the slightest evidence of suffering was visible: the suckers placed immediately beneath the injured part were invariably retracted; but all the rest, even in the same ray, still continued their action, as though perfectly devoid of participation in any suffering caused by the injury inflicted. Such apathy would indeed seem to be a necessary consequence resulting from the deficiency of any central seat of perception whereunto sensations could be communicated; nevertheless Ehrenberg insists upon the existence of eyes in some species of the star-fish, attributing the function of visual organs to some minute red spots visible at the extremity of each ray, behind each of which he describes the end of the long nerve which runs along the ambulacral groove as expanding into a minute bulb. We must however confess that the proofs adduced in support of such a view of the nature of these spots appears to us to be anything but satisfactory; and as we have already stated in the first chapter the physiological objections which may be urged against the possibility of any localised organ of sense being co-existent with a strictly nematoneurose condition of the nervous system, they need not be repeated here. The general sense of touch in the Asteride is extremely delicate, serving not only to enable them to seize and secure prey, but to recognise its presence at some little distance, and thus direct these animals to their food. A person who has been in the habit of fishing with a line in the shallow bays frequented by star-fishes, and observed how frequently a bait is taken and devoured by them, will be disposed to admit this; yet to what are we to attribute this power of perceiving external objects? It would seem most probably due to some modification of the general sensibility of the body, allowing of the perception of impressions in some degree allied to the sense of smell in higher animals, and related in character to the kind of sensation by which we have already seen the Actinic and other polyps able to appreciate the presence of light, although absolutely devoid of visual organs." (General Outline of the Animal Kingdom and Manual of Comparative Anatomy.')

Professor Edward Forbes, although he admits that the existence of ganglions in the nervous system of these animals is generally regarded as doubtful, seems, from the frequent recurrence of the terms 'eye' and 'eyelid,' to be of opinion that the specks above alluded to are visual organs. (History of British Star-fishes and other Animals of the Class Echinodermata.')

Our own opinion and observation are in favour of the views of Ehrenberg; and we think that those who have accurately watched the Star-Fishes which are furnished with these specks on the sea-coast will in general be irresistibly led to the conclusion that the organs, though not eyes in the strict sense of the term, serve the purposes of vision modified to the exigencies of the animal, enabling it to seek or avoid objects according to its will. Nor does analogy, in our view of the case, present any difficulty. We have only to consider that the centre is a head as well as a stomach, a condition that will hardly be denied to it, and the rays proceeding from it may be viewed as so. many antenna-(take those of the snail for example, with their ter minal ocular points, as in some degree analogous)-with visual dots at their extremities. This, at all events, may solve the problem of the destructive visitation of these animals to the baited line, more in unison with the analogies than the supposed existence of a general olfactory sense, of whose presence not the slightest trace has been observed.

The muscular system is generally present in the Echinodermata, but the organs of motion in them are various. The rays themselves are moveable, and in the free forms aid in the removal of the animals from place to place. Thus the common Star-Fish can bend its rays towards the upper or towards the lower surface of the centre or disc, and can approximate some while it extends others; so that they are widely divaricated laterally, and thus facilitate its advance in the water, or its passage through small spaces. In the common Star-Fish

these motions are slow, but in Ophiocoma they are comparatively rapid, and manifested in active contortions on some occasions. According to M. Sars, the young of Asterias sanguinolenta, which have four short club-shaped appendages or arms at their anterior extremity, move slowly but uniformly in a straight line with their fore arms foremost. Vibratile cilia are supposed to form the moving power in this case: the arms also enable the little animal to creep at a slow pace along the rocks. When the animal is more fully developed the power of swimming ceases.

Tiedemann considers that the power of moving the rays resides in the contractile skin. Meckel states that there are distinct muscles leading between the calcareous plates which form the floor of the rays. Dr. Sharpey has no doubt that the motions are partly effected by the skin, but he had himself observed a distinct band of muscular fibres running along the roof of each ray, between the coriaceous skin and peritoneal membrane when it is stripped off.

But the principal locomotive organs of the Echinodermata are the membranous tubes which can be protruded at will through the ambulacral apertures, and which have been termed the feet. The clearest description of this complicated and in some degree obscure apparatus known to us is that by Dr. Sharpey; and we therefore give it in his own words.

"These," writes Dr. Sharpey, treating of the membranous tubes or feet, are very numerous, and are usually disposed in regular rows: they contain a clear fluid, which is conveyed to them by a peculiar system of vessels. Each foot consists of two parts, an internal and generally vesicular portion placed within the body, and a tubular part on the outside projecting from the surface, and continues with the first through an aperture in the skin or shell. The tube is closed at the extremity, and terminates there in a sucker, which has usually the form of a disc slightly depressed in the centre. Both parts of the foot are evidently muscular, the fibres of the tubular portion being disposed in a circular and longitudinal layer; the cavity is lined with a transparent membrane, and the tubular part moreover receives an external covering from the epidermis. The foot is extended by the contraction of its internal vesicle, which forces the fluid into the tube; or when a vesicle is wanting, by the projection of a fluid into the tube from a communicating vessel. The tubular part is thus distended and elongated; it retracts itself of course by its muscular fibres; and when this takes place the fluid is forced back again into the vesicular or internal part. In progression the animal extends a few of its feet in the direction in which it desires to go, attaches the suckers to rocks, stones, or other fixed objects immediately in advance; then shortening its feet it draws its body in the wished-for direction. In the star-fish the feet are disposed in rows along the under surface of the rays, diminishing in size as they approach the extremity. There are usually two simple rows in each ray, and the vesicular part is for the most part deeply cleft into two lobes, as in A. aurantiaca. In other cases, as A. rubens, there are two double rows in every ray, and each foot has a round undivided vesicle. The canals or vessels which convey the fluid to and from the feet are all connected with a circular vessel situated in the vicinity of the mouth. This vessel lies immediately within the calcareous ring already described as connecting the rays at the commencement; from it a straight canal proceeds along the floor of each ray in the median line, and in its progress gives off lateral branches, which open into the vesicles of the feet. There are moreover connected with the circular vessel-First, a certain number of bodies (ten in five-rayed species) which Tiedemann compares to glands; they are very small, brown, sacculated organs, each opening by a small orifice into the circular vessel: Tiedemann supposes them to be the source from which the fluid filling the feet is derived. Secondly, pyriform sacs: in A. aurantiaca there are four groups of these; and each group consists of three or four sacs, which open by a common tubular pedicle into the circular vessel. In some other species there are five simple sacs. They are muscular, and Tiedemann conceives them to be the chief agents by which the fluid is forced into the vesicles of the feet, to which they are placed in a sort of antagonism. It would seem however that this purpose may be accomplished by other means; for according to Meckel's statement, and we may add our own observation, they are not present in all species. Lastly, the circular vessel receives the singular organ named the stone-canal or sand-canal by Tiedemann, who describes it as a membranous canal containing a friable mass of sandy or earthy matter, which commences by a wide origin on the inferior or internal surface of the calcareous disc already described as situate on the upper part of the body, descends in a duplicature of fibrous membrane, and opens by a narrow orifice into the circular vessel, the upper or wide end being closed by the disc. Ehrenberg has correctly remarked that this organ is not filled with an amorphous mass of earthy or cretaceous matter: he describes it as exhibiting a dense net-work of calcareous fibres, with hexagonal and pentagonal meshes, resembling in some respects the cavernous structure of the penis. The result of our own examination, in more than one species, is different still. We have always found the earthy matter forming a jointed calcareous tube. This tube, which is about the thickness of a surgeon's probe, is composed of rings of calcareous substance connected by membrane, so that viewed externally it is not unlike the windpipe of a small animal. On cutting it across however it is found to be more complex in struc

ture than appears externally; for it contains within two convoluted lamina of the same nature as its calcareous parietes. These lamina are rolled longitudinally they rise conjointly, or as one, from the internal surface of the tube, pass inwardly a certain way, then separating, are rolled in opposite directions, something after the same manner as the inferior turbinated bone of the ox. These internal laminae become more convoluted towards the upper end, where at last they, as well as the more external part of the tube, join the dorsal disc, appearing gradually to become continuous with its substance. The disc is perforated with numerous pores, which open into the tube. Tiedeman conceives the function of the sand-canal to be that of secreting the earthy matter required for the growth of the calcareous skeleton. Meckel considered this view as very improbable, and the description we have given does not tend to corroborate it. We must confess ourselves unable to offer more than mere conjecture as to the use of this singular structure. If the fluid contained in the feet and their vessels be sea-water (either pure or with an admixture of organic particles), which is probable from its chemical composition, may it not be introduced, and perhaps again discharged, through the pores of the disc and the calcareous tube, the porous dise serving as a sort of filter to exclude impurities?" (Cyclopædia of Anat. and Physiol.')

The reproduction of the Echinodermata appears to be monoecious, of that nature which Professor Owen terms cryptandrous hermaphro ditism. Ovaries are, as far as we are aware, the only organs relating to the generative functions hitherto discovered; but Fabricius, in his 'Fauna Groenlandica,' would seem to affirm that two individuals are necessary for the propagation of the species, and states that union takes place in the month of May-" congreditur oribus arctè connexis, altera supina." The ovaries, which appear to vary in number in different species, form in general an oblong cluster of tubes branching from a single stem, by which the whole is attached, and ending in circular dilated vesicles. In some species, Asterias aurantiaca for instance, the tubes form numerous bundles (about twenty), each of which is distinctly attached, so that they are not all connected by a single stem. In the Museum of the College of Surgeons, London, No. 2236 is a portion of a Star-Fish (A. rubens, Lam.) prepared to show the ovaria, ten in number, attached on each side of the base of each ray, near the angle of divergence; the ova are not developed in this specimen. No. 2237 exhibits an A. papposa, Lam., with the anterior parietes of one ray and the posterior parietes of another ray, dissected off, showing the ovaria with the ova at the commencement of their development. The ovaria are two in number in each ray, as in the preceding species, and are similarly attached on each side of the base of the ray, where they may be distinguished from the digestive and locomotive cæca by their greater opacity and granular structure. No. 2238 is the same species with the posterior parietes of the central disc removed, showing the commencement of the digestive cæca and the ovaries. No. 2239 is a portion of one of the rays of Comatula solaris, Lam., showing the ovarian receptacles occupying the inner side of each of the pinnæ, or articulate processes sent off from the rays. Three of the receptacles are laid open to expose the contained ova. ('Catalogue Physiol. Series.')

M. Sars states that the young of A. sanguinolenta immediately after birth have a depressed and rounded body, with four very short club-shaped appendages or arms at their anterior extremity, as above stated. When they are a little more developed papillæ disposed in five radiating rows on the upper surface may be distinguished. At the expiration of twelve days the five rays of the body, which up to that time had been rounded, begin to increase; and at the conclusion of eight days more the two ranges of feet or tentacula are developed under each ray, and assist in the locomotion of the animal by alternate elongation and contraction and performing the office of suckers.

The integuments of a Star-Fish are-1, a leather-like tough membrane in which portions of calcareous matter, which may be termed the skeleton of the animal, are imbedded; 2, an external membrane of a softer texture; 3, certain appendages. "The calcareous pieces," writes Dr. Sharpey, 'Cyclo. of Anat. and Physiol.,' "form inferiorly a ring round the mouth and a series of transverse segments placed in succession along the floor of each ray. The first of these segments is connected with the ring; they decrease in size as they approach the point or distal end of the ray, and openings are left between them for the passage of the feet. In the Asterias rubens, which has five rays, the central ring consists of ten larger and five smaller pieces, the former disposed in pairs opposite the commencement of the rays, the latter corresponding to the angles between the rays. The segments of the rays are symmetrical; in the species mentioned they consist of two oblong pieces united in the median line, and two smaller ones placed laterally. On the sides of the ray the calcareous substance is disposed as it were in ribs; these rise from the floor at first nearly parallel with each other, and are connected by cross bars, but on approaching the upper part or roof of the ray they cross in all directions and form an irregular net-work, the intervals of which are occupied by softer integument. The ribs and bars are made up of small pieces joined by plane but oblique surfaces, a mode of construction calculated to admit of their being lengthened and shortened upon one another, and thus to allow the cavity they surround being dilated and contracted. A broad calcareous disc is situated on the upper surface of the body in the

angle between two of the rays, which is connected internally with the sand-canal. The calcareous pieces are of a homogeneous structure without cells or fibres; they consist, according to Hatchett's analysis, of carbonate of lime, with a smaller proportion of phosphate of lime. The coriaceous membrane which connects the pieces of the skeleton is made up of white glistening fibres. It is contractile and irritable, for it slowly shrinks on being scratched with the point of a knife, or when it is cut through. The external membrane is much thinner and softer than that just described; in various parts it is coloured, or in these parts there is a coloured layer underneath it. The appendages or processes on the surface of the body are of three kinds. First, calcareous spines; these are found over the whole surface, except the grooves for the feet. They are attached by a moveable joint at their base to the calcareous pieces of the skin, and are invested by the external soft membrane nearly as far as their point. Those on the upper surface are solitary, short, and for the most part club-shaped, their broader summit being marked with radiating points; whence they were named stelliform processes by Tiedemann. On each side of the groove for the feet the spines are thickly set; these in A. rubens have three rows, in the middle and innermost of which they are placed three deep. On this part of the surface they are also longer and pointed. The spines are slowly moved at the will of the animal. The appendages of the second kind are of a very singular nature; they have the appearance of pincers of crab's claws in miniature, and were described by Müller as parasitical animals under the name of Pedicellaria. Monro gave the name of antennæ to analogous organs which are found on the Sea Urchin. They probably do not exist in all species, for Tiedemann makes no mention of them in his description of A. aurantiaca. In A. rubens they cover the surface generally, and form dense groups round the spines. Each consists of a soft stem, bearing on its summit, or (when branched) at the point of each branch, a sort of forceps of calcareous matter not unlike a crab's claw, except that the two blades are equal and similar. When the point of a fine needle is introduced between the blades, which are for the most part open in a fresh and vigorous specimen, they instantly close and grasp it with considerable force. The particular use of these prehensile organs is not apparent; their stem, it may be remarked is quite impervious. The third sort of appendage consists of those which are named the respiratory tubes." In the other Echinodermata the same general construction of the skeleton may be observed; but the modifications differ with the forms. In some it consists of hundreds of pieces disposed in various patterns, and fitting with the most minute accuracy. In some these pieces are soldered together, as in the calcareous central purse from which the arms of the Ophiure radiate; and in others they are united by ligaments, as in the rays of these Ophiura, the Gorgonocephali, and the Encrinites.

The sudden and voluntary act of dismemberment by which many of the Echinodermata will save their central disc at the expense of their rays or arms, must have struck those who have observed these animals in their native seas, as well as the length of time during which the severed parts still continue to be endowed with motion. This power of dismemberment seems to be carried to its fullest extent in Ophiocoma and Luidia. The following account by Professor E. Forbes of an attempt to capture a species of the last genus is a good illustration of this property: :

"It is the wonderful power which the Luidia possesses, not merely of casting away its arms entire, but of breaking them voluntarily into little pieces with great rapidity, which approximates it to the Ophiure. This faculty renders the preservation of a perfect specimen a very difficult matter. The first time I ever took one of these creatures I succeeded in getting it into the boat entire. Never having seen one before, and quite unconscious of its suicidal powers, I spread it out on a rowing bench, the better to admire its form and colours. On attempting to remove it for preservation to my horror and disappointment I found only an assemblage of rejected members. My conservative endeavours were all neutralised by its destructive exertions, and it is now badly represented in my cabinet by a discless arm and an armless disc.

"Next time I went to dredge on the same spot, determined not to be cheated out of a specimen a second time, I brought with me a bucket of cold fresh water, to which article star-fishes have a great antipathy. As I expected, a Luidia came up in the dredge, a most gorgeous specimen. As it does not generally break up before it is raised above the surface of the sea, cautiously and anxiously I sunk my bucket to a level with the dredge's mouth, and proceeded in the most gentle manner to introduce Luidia to the purer element. Whether the cold air was too much for him or the sight of the bucket too terrific I know not, but in a moment he proceeded to dissolve his corporation, and at every mesh of the dredge his fragments were seen escaping. In despair I grasped at the largest, and brought up the extremity of an arm with its terminating eye, the spinous eyelid of which opened and closed with something exceedingly like a wink of derision. Young specimens are by no means so fragile as those full grown, and the five-armed variety seems less brittle than that with seven arms. Like other star-fishes it has the power of re-producing its arms."

With regard to the power of restoration, few collectors have not come into possession of a specimen with a budding or growing ray

occupying the place of a lost one. [ENCRINITES.] Jussieu, Guettard, and Gerard de Villars brought to Reaumur specimens of Star-Fish with four large rays and a small one still growing; they found others, he tells us, with only three large rays and two very small ones; and others with two large rays and three very small, and, as it seemed, very young ones. More than once they met with a large ray from which four young rays had begun to sprout. Reaumur speaks of the fact as being well known to the fishermen, and in allusion to certain experiments which Jussieu and Guettard had been carrying on he remarks that the portions into which they had divided the animals appeared to go on well, the wounds healed and consolidated; but he adds that those who made the experiment were obliged to limit their stay on the coast to about fifteen days-too short a period, he observes, to trace the progress of a reproduction which apparently requires several months, or perhaps even more than a year for its completion. Although the Echinodermata have so great a power of reproducing lost parts, they present no indications of any power of increasing separate individuals by gemmation as witnessed in the Acalephæ and lower animals. As in the Acalephæ, the embryo of the Echinodermata pass through several forms before arriving at maturity. The following is an outline of the process in the Asteriada:-"From the accounts of the development given by different trust-worthy observers, there can be little doubt that the process takes place after at least two very diverse plans. The first and simplest of these has been witnessed by Sars in the Echinaster rubens; and the observations of Agassiz are on the whole in accordance with those of that industrious naturalist. In the early stages the segmentation of the yoke takes place as in other animals; and the embryo comes forth from the egg soon after it has attained the state of the mulberry mass,' and swims freely about, by means of the cilia with which it is covered, in a sort of marsupial chamber which is formed by the drawing together of the rays of the parent around its mouth. Soon after its emersion, the embryo begins to put forth an organ of attachment, resembling the stem of a Crinoid; this at first possesses two tubercles, then three, then four, with a fifth smaller one between them. At the same time, the principal mass becomes flattened, and shapes itself into five lobes surrounding a central disc; thus sketching out the body and rays. When in this state it attaches itself to fixed objects by its organ of adhesion; but if detached, it swims through the water by the action of the cilia with which the body and arms are clothed; so that it bears a strong analogy to the Pentacrinus in process of conversion into a free moving Comatula. At the same time, five double rows of small tubercles may be perceived radiating from the centre of what is to become the ventral surface of the body; these gradually elongate themselves, and become cirrhi, each furnished with a sucker at its extremity. A peculiar tubercle is also seen at the edge of each of the five lobes of the body; and this is the rudiment of the ocellus, which is afterwards found at the extremity of each ray. As development proceeds, the primitive organ of adhesion gradually decreases in size, and the animal creeps by means of its cirrhi; and at last the pedicle is drawn (as it were) into the body, the lobes of the body lengthen into rays, the animal loses its ciliograde progression, and the ordinary characters of the Star-Fish become apparent. The progress of the internal organisation is thus described by Agassiz:-The earliest deposit of calcareous matter takes place around the prominent tubercles of the lower surface; at first in the condition of little isolated crystals, which are formed as nuclei in the cells; and then as a network formed by the coalescence of several of these. Of these networks there are at first ten, symmetrically disposed on the ventral surface, in a manner corresponding to the arrangement of the solid plates in Crinoids; but they gradually increase in number, and more distinctly mark out the rays; new ones being interposed in pairs between those already existing, and small spines projecting from the older ones. The calcareous deposit in the dorsal surface, on the other hand, seems to proceed from a central nucleus above the yolk-mass. The progress of development is obviously from without inwards; the cells on the surface of the yolk-mass being the first to undergo metamorphosis into the permanent structure. Those occupying the central part of the body and pedicle undergo liquefaction, and a kind of circulation is seen in the latter. Gradually what remains of the yolk-mass is more distinctly circumscribed in the interior of the animal, and forms a central cavity with prolongations extending into the rays; but it is not until the pedicle has contracted itself into a mere vesicle that the mouth is formed, by the thinning-away of the envelope of the yolk-mass on the lower surface, a little to one side of the base of the pedicle; and it is not until after the formation of the mouth, that the nervous ring can be traced, with its prolongations extending to the ocelli at the extremities of the rays.'

"The second plan of development seems much more conformable to what will be presently described as taking place in the Ophiuride and Echinide; for the body first developed from the embryonic mass is a larva, of which little remains in the permanent structure, and the Star-Fish is budded off, as it were, from the anterior extremity of this. This larva, which has received the name of Bipinnaria from the symmetrical wing-like arrangement of its natatory organs, presents much more resemblance to an Articulated, or to a Vertebrated, than to a Radiated animal. Its body is elongated, and carries at its anterior

extremity the portion of the yolk-mass not yet metamorphosed, from which the Star-Fish is afterwards to be developed; and into the cavity of this a passage is formed, through what may be termed the mouth of the larva, which opens in the middle of a transverse furrow, whilst another tube passing forth from it seems to answer to an intestine. On either side of the anterior portion of the body are six or more narrow fin-like appendages, which are fringed with cilia; and the posterior part of the body is prolonged into a sort of pedicle, bilobed towards its extremity, which also is covered with cilia. The organisation of this larva seems completed, and its movements through the water are very active, before the mass at its anterior extremity presents anything of the aspect of the Star-Fish; in this respect corresponding with the movements of the Pluteus of the Echinida. The temporary mouth of the larva does not remain as the permanent mouth of the Star-Fish; for it is on what is to become the dorsal side of the body; and the true mouth is subsequently formed by the thinning away of the integument (which has completely inclosed the yolk-mass) on the ventral surface. The young Star-Fish is separated from the bipinnarian larva, by the forcible contractions of the connecting pedicle, as soon as the calcareous consolidation of its integument has taken place, and its true mouth has been formed, but long before it has attained the adult condition; and as its ulterior development has not hitherto been observed in any instance, it is not yet known what are the species in which this mode of evolution prevails. The larva continues active for several days after its detachment; but there is no reason to believe that its existence is prolonged for any considerable time; and as the Star-Fish is not formed by gemmation from it, but from a portion of the yolk-mass which remained unconsolidated after its completion, it is obvious that the larva does not stand in the same relation to the Star-Fish, as the hydraform polype to its medusa-bud." (Carpenter, Principles of Physiology.') Müller (Ueber die Larven und die Metamorphose der Echinodermen,' 1848) has also described the process of embryonic development in the Ophiuride and Echinidæ. In these the embryo issues forth from the ovum as soon as it has attained by the repeated segmentation of the yolk the condition of the 'mulberry mass,' and the superficial cells of this are covered with cilia, by whose agency it swims freely through the water. So rapid are the processes that not more than 24 hours elapse between fecundation and the exit of the embryo. Shortly after its emersion the embryo changes from the spherical into a sub-pyramidal form with a flattened base; and in the centre of this base is a depression, which gradually deepens so as to form a mouth that communicates with a cavity in the inside of the mass. The pyramid is at first triangular, but it afterwards becomes quadrangular, and the angles are greatly prolonged round the mouth (or base), whilst the apex of the pyramid is sometimes greatly prolonged in the opposite direction, but is sometimes rounded off into a kind of dome. This body is strengthened by a frame-work of thread-like calcareous rods. In this condition the embryo swims freely through the water propelled by the cilia which clothe the angles, and the projecting arms. The creature has at this stage received the name of Pluteus. The Pluteus of the Ophiura and Echinus differ but little at first in their general form and structure. Each species however has its distinctive characters. In this stage the Pluteus resembles the Acalephæ; its probosciform mouth resembling the Medusa and its cilia the Beröe. [ACALEPHE.] The Pluteus gradually loses its Acalephoid characters, the jaws and teeth and calcareous plates slowly developing; and it thus passes into its

true Echinodermatous form.

Systematic Arrangement.-Most systematists have given classifications of the Echinodermata.

Link, in his volume De Stellis Marinis' (fol., Leipzig), arranges and figures a considerable number of species, in the method of which the outline is here given.

Section I. De Stellis Fissis.

Class 1. Oligactis (Star-Fishes with fewer than five rays).
Genera, Trisactis, Tetractis.

Class 2. Pentactinodos (Quinquefid Star-Fishes).

Genera, Pentagonaster, Pentaceros, Astropecten, Palmipes, Stella coriacea, Sol marinus, Pentacdylosaster.

Class 3. Polyactinodos (Multifid Star-Fishes).

Genera, Hexactis, Heptactis, Octactis, Enneactis, Decactis, Dodecactis, Triscaidecactis.

Section II. De Stellis Integris.

Class 1. Stellarum Vermiformium.

Genera, Stella lumbricalis, Stella scolopendroides. Class 2. Stellarum Crinitorum.

Genera, Decacnemos, Triscaidecacnemos, Caput-Medusa. Class 3. Astrophyton.

Genera, Arachnoides, Astrophyton costosum, Astrophyton scutatum. Linnæus divided his genus Asterias into the following sections:1. Integra.-Example, Asterias Luna, the only species.

2. Stellata. This section contained nine species. Example, Asterias papposa.

3. Radiata Containing six species. Examples, Asterias Ophiura, A. Caput-Medusa.

Position of the genus between Medusa and Echinus.

Gmelin arranged the genus in three sections also, retaining the names of Linnæus for the last two; but altering that of the first, under which he includes four species, to Lunatæ.

Position of the genus, between Physsophora and Echinus. Lamarck, who, according to De Blainville, "a suivi à peu près les erremens de Link dans la distribution systematique des Stellérides," arranged them as the first section or family of the Echinodermatous Radiata, and separated them into the genera Comatula, Euryale, Ophiura, and Asterias.

Ophiura is divided by Lamarck into two distinct sections; 1st, Those species which have the rays rounded or convex on the back, 2nd, Those species which have the rays flattened on the back, that is, above as well as below. Then comes a crowd of species under the title of "Espèces que je n'ai point vues."

Agassiz divides the Ophiura into five sections :

1. Ophiura. Those species which have the disc very much depressed, the rays simple, scaly, and furnished with very short spines, and embracing or close down upon the rays. Examples, Ophiura texturata, O. lacertosa, Lam. 2. Ophiocoma. Those species which differ from the preceding by having very long and moveable spines upon the rays. Examples, Ophiura squamata, O. echinata, Lam. 3. Ophiurella (Fossil only).-Those species whose disc is hardly distinct. Examples, Ophiura carinata, Munst.; O. Egertoni, Brod. 4. Acroura (Fossil only).--Differing only from Ophiura in having spines on the sides of the rays instead of scales; while the rays themselves are very slender. Examples, Ophiura prisca, Münst.; Acroura Agassiz, Münst.

5. Aspidura (Fossil only).—Having the upper surface of the disc covered by a star of ten plates, whilst the rays, which are proportionally stout, are surrounded by imbricated scales. Example, Ophiura loricata, Goldf.

Asterias is arranged by Lamarck under the following divisions:— 1. Those species which have the body scutellated. These are numerous, and comprise the genera Scutaster, Plataster, Palmaster, and Solaster of De Blainville.

2. Those which have the body radiated, consisting of numerous species also, and comprising the genera Solaster and Pentaster of De Blainville. The Stelleride, in Lamarck's arrangement, are immediately followed by the Echinidæ.

Cuvier makes the Echinodermes the first class of Zoophytes, and the Pédicellés the first order of that class, observing that Linnæus established three genera of them (meaning apparently the three divisions above stated), which are very natural, but numerous enough, and comprise species sufficiently varied to be considered as three families.

Cuvier divides the species into :—

Les Astéries (Asterias, Linn.), commonly called Sea-Stars. He recognises some of the genera of Leach and Lamarck, and observes that the Encrinites (Encrinus, Guettard) ought to be placed near the Comatule.

The Oursins (Echinus, Linn.) immediately follow the Sea-Stars.
De Blainville divides the Stelliridians into three families:-1.

Those with a stelliform body; 2, those with a disciform body; 3, those with a cupuliform body.

I. Asteridians.

Genus Asterias, comprising the following divisions or sub-genera :— A. Species whose body is pentagonal, and but little or not at all lobated on its circumference; the angles being fissured (Les Oreillers). Example, Asterias Luna.

B. Pentagonal species: delicate, and, as it were, membranous (Les Palmastéries-Palmipes of Link).

C. Quinquelobated species, which are not articulated on the circumference. Example, Asterias minuta, Linn. (Pentaceros, Link; Asterina, Nardo.)

D. Pentagonal species more or less lobated and articulated at their circumference (Les Scutastéries, ou Platastéries). Example, Asterias tessellata. [ASTERIAS.]

De Blainville remarks that the species of this section, many of which exist in the European seas, do not appear to him to have been examined by zoologists with sufficient accuracy; and he thinks that many species have been confounded under the same name. E. Species deeply divided into five rays (Pentastéries).

1. Free Asterencrinidians. Example, Comatula. [COMATULA,] 2. Fixed Asterencrinidians.

Genera, Encrinus; Phytocrinus; Pentacrinus; Apiocrinites; Poteriocrinites; Agathocrinites; Actinocrinites; Rhodocrinites; Platycrinites; Caryocrinites; Marsupites; Pentremites. [ENCRINITES.]

Agassiz also divides the Stellirideans into three families or principal sections, but he gives them different names.

1st. Asterians, consisting of those species which have for their digestive organ a single orifice surrounded by suckers, but deprived of teeth; a madreporiform tubercle on the back between the two posterior rays, and deep furrows occupied by many rows of pedicles, going from the mouth to the extremity of the arms.

2nd. Ophiurians, comprising those whose body forms a flattened and distinct disc, to which are annexed more or less elongated or even ramified rays, deprived of furrows on their lower surface.

3rd. The Crinoidians, having two separate, but closely approximated orifices to the intestinal canal; and being for the most part fixed by the dorsal surface, by means of an articulated pedicle.

Before we enumerate the genera into which this zoologist divides Asterias, we must notice the division of M. Nardo, who had previously proposed the following:-Stellaria (A. aranciaca-A. calcitrapa); Stellonia (A. rubens—A. glacialis); Asterina (A.exigua—A. minuta); Anseropoda (A. membranacea-A. rosacea); Linkia (A. lævigata-A. variolosa).

The following is the division of Agassiz.

1. Asterias (Astropecten, Link; Crenaster, Llhuyd.; Pentaster, Bl. ; Stellaria, Nardo).

2. Calaster, Ag., differing from the preceding in having the interior cavity circumscribed by plates disposed like those of the Echini, at the summit of which may be perceived a star with ambulacra. A genus approaching the Crinoidians in its organisation, whilst its general form is that of the true Star-Fishes. Example, only one species, and that fossil, C. Couloni, Ag.

3. Goniaster, Ag. (Scutaster or Plataster, Bl.). Examples, Asterias tessellata, Lam., A. equestris, Linn.

4. Ophidiaster, Ag. Example, A. ophidiana, Lam.

5. Linkia, Nardo. Example, A. variolata, Lam.

6. Stellonia, Nardo, (Pentaster in part and Solaster in part, Bl.). Examples, A. rubens; A. glacialis; A. endeca; A. papposa; A. Helianthus, &c.

7. Asterina, Nardo (Asterias, sect. C., Bl.; Pentaceros, Link). Example, A. minuta.

8. Palmipes, Link (Palmaster, Bl.; Anseropoda, Nardo). Example, A. membranacea.

9. Culcita, Ag. (Oreiller, Bl.). Example, A. discoidea.

In 1840 Müller of Berlin read his paper on the genera of StarFishes to the Berlin Academy, in which the anus or anal pore is employed as characteristic of family distinction. This aperture is described as present in all Star-Fishes, excepting Asterias proper and Hemichemis, which, according to Mr. Forbes, seems to be identical with his previously established Luidia. "His genus Crossaster also," says Mr. Forbes, "is my Solaster, published a year before. Several generic names, previously adopted by Agassiz and Nardo, are wantonly changed; thus Uraster is turned into Asterocanthium, and Palmipes into Asteriscus, with which he unites Asterina. In this paper Müller maintains that one of the five intermediate inferior plates of the Ophiuride bears a madreporiform tubercle, or rather corresponds to that body, a view which I am not inclined to adopt." With regard to Solaster, we have seen how long ago Solastérie was used by De Blainville; but the practice of wantonly changing names is productive of so much confusion that it cannot be too strongly reprobated. Mr. Forbes admits, as all indeed must, that the generic characters in Müller's papers are excellently drawn up; and no difference of opinion can exist as to the great general value of the memoir.

The following arrangement is that of Dr. J. E. Gray, in the 'List of