Inestinal ends; mouth circular or angulated; apex of the tail in the male Worms. terminated with a purse-like sheath, whence the penis is protruded.

The S. gigas (Plate VI. fig. 4) may be considered the type of the genus. It attains the length sometimes of 2 or 3 feet, and is as thick then as a man's little finger: and yet our own shoulder to think that monstrous worm!—not only the canker-worm, inhabitant of the cellars of houses, where it lies rolled up, battering on them, but also prevalent unspeakable torture. It afflicts other animals, as the dog and wolf, and is not confined to the kidneys. It is often found of a deep red colour, dependent undoubtedly on the blood it has sucked from its victims. Of worms excreted with the urine, see cases very interesting to the "greedy hunters after monsters," in Le Clerc's History, p. 264, et seq. Also the Cyclopaedia of Practical Medicine, vol. iv., p. 516.

Genus PHYLLOPTERA.—Body round, elastic, attenuated at both extremities; mouth circular; tail of the male deflexed, winged on each side, ending in an inferior vesicle; penis protruded from a tubercle. The species are few and intestinal.

Genus SPIROPTERA.—Body round, elastic, attenuated at both extremities; mouth circular; penis emerging from between the wings of the spirally involute tail. The species are numerous. One has been said to occur in the urinary bladder of man.

Genus COCCULINACEA.—Body round, elastic, attenuated behind; mouth circular, placed under a striated hood; the male organ a tubercle. The species infect the stomach and intestines of various fish.

Genus OXYURIS.—Body round, elastic, the posterior part of the female subulate; mouth circular; penis sheathed. The species are few, and confined to quadrupeds. One is very troublesome to the horse; and the worm which perhaps annoys man more than any other (Ascaris vermicularis) has lately been removed to this genus.

Genus TRICOCHEPHALUS.—Body round, elastic, the anterior capillary extremity suddenly succeeded by a thicker portion; mouth circular; male organ simple and sheathed. "The species inhabit the large intestines, particularly the cecum of the mammalia; they do not occur in either birds or fish."—Bellingham. The T. solium (Plate VI. fig. 2) is said by Rudolph to be very common in the large intestines of mankind. It is about two inches in length, only one third of which is taken up by the thick portion of the animal. This portion has a spinal form in the male, which is furnished with a small penis, protruding from near the tail. In the female, which is oviparous, the thick portion is straighter, and is simply pierced at the extremity. On the continent it would seem that this is the worm which is met with the most frequently in the human intestines. Indeed some of the most distinguished helminthologists state, that they scarcely ever fail to find them. The large intestines are their principal seat, but more especially the appendix vermiformis of the cecum. Though I have frequently and carefully sought for this worm, I have only once been able to find it. In this instance it was lodged in the mucus filling the appendix of an emaciated and cachetic girl, who had been much exposed to want and hardship." (Dr Hodgkin's Lectures, &c., vol. i. p. 207.)

Dr Bellingham's experience is not a different case. A similar complaint by the Irish.—See his Catalogue of the Entozoa indigenous in the Mop. of Nat. Hist., vol. iv. p. 343, &c.

Genus CAPILLARIA.—Body round, elastic, very slender, growing insensibly larger to the posterior extremity; mouth a mere point; male organ a simple sheathed thread. Named Capillaria by Zeder. The species are found principally in birds, next in the mammalia, and very rarely in reptiles and fish.

Genus FILARIA.—Body round, elastic, linear, elongate; mouth circular; male organ a simple spiculum. The species are numerous, and infest many invertebrate as well as vertebrate animals. They are principally intestinal, but a species has been found in the eye of the horse, another in the eye of man, and another in the bronchial glands. The most celebrated species (F. mediascens, or Guinea-worm, Plate VI. fig. 1) burrows in the cellular tissue under the skin. It was well known to the ancients; and a portion of the history of it given by Paulus Aegina may be quoted: "In India and the countries above Egypt, there are certain little demons, animals like worms, in the muscular parts, as the arms, thighs, and legs, and in children they are in the sides, and plainly move under the skin. But after some time a place nigh the end of the worm suppurates, the skin breaks, and the head of the little dragon comes out. While it is drawn out it causes pain, and especially intestinal when it is broken. Wherefore some say that a leaden weight should be hung to the dragon, that the falling out should not be heaps, but in pieces. Others understand these, because by the weight of the lead the worm is broken, and cannot resist pains, order the part to be put in warm water, by the fomentation of which the worm comes out, and is drawn out piecemeal by the fingers." Le Clerc's Hist. of Worms, p. 212. Freind's Hist. of Physick, vol. i. p. 49, &c. Mr Hutcheson gives an account of his having extracted one that measured 3½ yards in length. Good's Study of Medicine, vol. vi. p. 653.

The eggs of the Nematoida, with a very few exceptions, are of an oval shape when mature. The changes which they undergo in the process of hatching have been minutely described by Siebold, but we can only mention one or two particulars. The covering or shell is colourless and single, but frequently double. The vitelline mass is whitish, and contains, in unripened eggs, a well-marked proliferous vesicle with a proliferous spot. When these immature eggs have passed into the uterus, remarkable changes begin in the yolk, which at this period is a mass of delicate granulations, set in a uniform manner, and completely filling the envelope of the egg. The proliferous vesicle, deeply hidden in the vitelline mass, is obscurely seen, and soon afterwards disappears. On its disappearance, the physiologist is surprised to observe on the vitelline mass those remarkable grooves, the existence of which he had never suspected in any invertebrate animal, and least of all in the Entozoa, and which had been seen only in the eggs of the Frogs (Batrachians) by Prevost and Dumas, and some other observers.

The Intestinaceae constitute the second class of zoophytes in Cuvier's arrangement. He divides them into two orders, so different in their organization that they seem rather to deserve the rank of classes. The first order, the Intestinaceae communes, have an alimentary canal divided in a distinct abdominal cavity, with a mouth and anus; but the body of the constituents of the second order, the Int. parenchymateux, contains within its parenchyma only ill-defined viscera, having the resemblance mostly of vascular ramifications; and sometimes even these traces of organism are imperceptible. We shall here present a brief sketch of Baron Cuvier's system.

Order 1.—The Cavitaires, Cuv.

Epizoa. Owen.

This nearly corresponds with the order Nematoida of Rudolph, embracing also the genera Linguatula or Pentastoma, and the Priocnemidae, which Rudolph has placed among his fictitious or obsolete species. Cuvier believes that at the end of this order we ought to classify, as a distinct family, the Lernæa of Linnaeus, or Epizoidea of Lamarck; but it is now proved that these are really crustaceans, which, in their infancy, do not differ from the new-born Cyclops, and are equally capable of swimming about; but assuming the character of adhesive parasites, they suffer a deformity that increases with their growth, and conceals their nobler alliances, for they never acquire all the members with which the more normal crustaceans are provided. Of all the paradoxical creatures which the naturalist meets with in his researches, there is none that surpasses or equals these in eccentricity, none more at variance with our notions of animal conformation, and exhibiting less of that decent proportion between a body and its members which constitutes what we choose to call symmetry and beauty. Of these monsters we shall attempt no description; but the figures of a few of them, given by Cuvier, figs. 13-17, will convey some idea of their shape and variety. They are all external parasites, living on the skin and on the gills of fish, to which they adhere by hooked grasps or claws; and it is presumed that they injure the fish by sucking out their blood. Bermeister, who places them

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1 On the Entozoa of insects consult Léon Dufour, in Ann. des Sc. Nat. s. s. tome vii. p. 5. 2 Its exterior figure might induce us to place after Filaria the genus Trichina of Owen, found in myriads in the voluntary muscles of man, but its simplicity of structure scarcely raises it from among the Infusoria, more especially from above the eels of vinegar and paste. On this interesting worm see the elaborate essay of Owen in Trans. of the Zoological Society, vol. i. p. 316; and in Cyclop. of Anat. and Physiology, ii. p. 114; Hodgkin's Lectures, vol. i. p. 211; and several essays in recent volumes of the Lancet and Medical Gazette. 3 See Bardach's Traité de Physiologie, vol. iii. pp. 59-64. 4 Régne Animal, iii. pp. 245-274. 5 The males however retain their freedom and powers of locomotion at all ages. See Cuvier, Rég. Anima., iii. p. 255, note 2; and Bardach's Traité de Physiologie, tome iii. p. 130. Intestinal among the Siphonostomous Crustacea of Latreille, gives the following synopsis of their genera:

I. FAMILY PENELLINA.

* Body more or less twisted in an angular manner, unequally thick, and furnished anteriorly with bifurcated arms. † Three long cornuous arms placed around the mouth; the two anterior, or all the three, forked; the oviferous sac resembling a spirally twisted cord. Lernocera, Okem. †† Four soft and fleshy appendages placed around the mouth; the anterior forked; oviferous sac cylindrical. Lernocera, Blainv. ** Body straight and of equal thickness; four pairs of cutaneous prominences toward the anterior part, which is prolonged into the form of a neck. † Without arms; nor is the tail penniform. Pennicula, Nordm. †† With arms, and a penniform tail. Penella, Okem.

II. FAMILY LERNEOIDA.

Body with two pincers or prehensile appendages, situated behind the proboscis, and without swimming feet, which are sometimes represented by simple cutaneous prolongations.

* Prehensile apparatus simple, situated at the point of union between the trunk and the neck. Anchorella, Nordm. ** Prehensile apparatus elongated, composed of appendages which have the shape of arms, and which are united together near their extremity. † Cephalothorax prolonged into a neck. § Pincers with booklet placed on the lower part of the neck, between the arms. Trachelastus, Nordm., Lernantoma, Blainv. §§ Pincers with booklet placed at the upper part of the neck, almost behind the head. Branchiella, Nordm. †† Cephalothorax short, rounded or heart-shaped; pincers, with booklet, placed immediately in front of the arms. § Arms very long and thin; the abdomen elongated, and not jointed. Lernopoda, Blainv. §§ Arms very long and thin; the abdomen circular and jointed. Acytherea, Nordm. §§§ Arms short and thick; abdomen not jointed, and verrucose. Basanieta, Nordm.

*** No prehensile organs in the shape of arms. † Tentacula of two or three joints not formed of articulated feet, armed with booklet; a pair of jaws and two palpi. Chondrocanthus, Cuv. †† Tentacula with six joints; an eye on the top of the head; three pairs of jointed pincers behind the mouth, which is conical. Lernanthrope, Blainv.

After this family there follow, in the system of Cuvier, some genera of marine worms, which are not parasitical, and are undoubtedly members of the family Planaria. The Nemertes had been previously characterised by Sowerby, and by him named Linnaeus. It is remarkable for the extraordinary length to which it grows. We have been informed that specimens of thirty feet long have been seen, and indeed some in our possession which, when extended, could not be less than fifteen or twenty. It is to be found under stones, coiled up in an intricate mass of a purplish-brown or claret colour, smooth and glossy, of nearly uniform calibre throughout, and free of wrinkles or joints. The head is distinct enough; and underneath it there is a long slit, which is the mouth. The intestine runs the entire length of the body; and, what is very curious, we have a specimen which has swallowed a periwinkle, the shell forming a knob near the middle of the body, reminding us of the appearance of a gorged snake. After the Nemertes, says Cuvier, we ought probably to place the Turbellaria of Renieri, which are equally large and very much elongated, but which have a small mouth pierced under the anterior extremity; and the Ophioceratae of Quoy and Gaimard, distinguished by having the apex of the snout cleft; and the Cerebratulae of Renieri, which differ from these merely in the comparative shortness of the body.

This order is divided into four families. The first is co-equal with the Acornaecephala of Rudolph; the second embraces the Trematoda of the same author, with some additions. One of the most extraordinary is the Hectocotylus of Cuvier, a long worm, compressed and enlarged at the posterior extremity, upon which is the mouth, whose inferior surface is garnished with numerous suckers, arranged in pairs; and at the posterior extremity there is a sac, filled with folds of the ovicord. One species of this resides itself in the flesh of the sea-polypos (Octopus) is four or five inches long, and has 104 suckers; another of smaller size, and with seventy suckers, is the parasite of the Argonauta. The Aspidogaster of Baer is a minute parasite of the mussel, distinguished by having under the belly a lamina, hollowed with four rows of little pits. In this family also Cuvier arranged a multitude of animals which were formerly comprised in the genus Planaria of Müller. They are little worm or leech-like animals, with a soft, compressed, or foliaceous body, found both in the sea and in fresh waters. There is no abdominal cavity. The mouth, placed in the belly near its middle, is furnished, in many, with a protusible proboscis, which leads into an intestine of a dendritic character, and whose ramifications permeate the whole body. A vascular network occupies the sides; and there is, posterior to the oral aperture, a double system of generative organs. The species are amoeboid, like the snails, and oviparous. The head is ornamented in most with branchiae, and in others, probably eyes. They are voracious creatures, feeding on animal matter; but, above all, they are remarkable for the facility with which they reproduce any part of the body that may have been lost by accident, or cut away by the curious experimenter. In this wonderful power they equal the Hydra. The species and races are extremely numerous, and admit of much complicated classification. Dugès distinguishes them into the typical Planarias, with a ventral aperture; the Prostomes, which have one orifice at the interior, and another at the posterior extremity; and the Derostomes, in which the oral aperture is beneath, but placed considerably forwards.

The third family of the intestinal Parenchymateux is named the Teniodidae. It combines the orders Cestoidae and Cystidae of Rudolph. The fourth family is the Cestoidae, and embraces only the genus Ligula of Bloch, parasitical worms found in the intestines of some birds, and of various fresh-water fish. They appear the simplest of all the Entocea. The body is like a long ribbon, obtuse in front, marked with a longitudinal stria, and finely scored crosswise. There is apparently no external organ; and in the interior we see nothing but the ova scattered in the parenchyma. The species which infests the brown grows to five feet in length; and Cuvier says that the worms are considered in some parts of Italy an agreeable food.

In the bowels of some seals, and birds which live upon fish, there are found certain worms very like the Ligula, but in which genital organs have been developed, and even a head similar to that of the Bothryoccephalus or tape-worm. Rudolph hazards the conjecture that these worms of birds are identical with the Ligula of the fish, which have acquired their fuller organization by passing from the intestines of the cold-blooded animal into those of a warm-blooded one. There are some facts in the history of other tape-worms which give a colour to this conjecture; and we may just call attention to its bearing upon the question of their equivocal generation.

[Professor Owen's summary of the characters of the class Ephora, and its three orders, is this:—]

Body chitinous, vermiciform, subarticulated, not always symmetrical; with antennae and articulated limbs, terminated either by suckers, hooks, or bristles. Vascular system diffused; white blood. No respiratory organs. Dioecious. Males small or rudimentary; females with external pendent ovaries. Metagenesis resulting in a usually permanent parasitic attachment on the bodies of fishes.

ORDER I. CEPHALUNA. Attachment by cephalic processes, sometimes numerous and complex. Gen. Peniculus, Lernexa, Chondracanthus, Lernocera, Penella.

II. BRACHIUNA. Attachment by a sucalorial disk at the concentric extremities of the last pair of thoracic limbs. Gen. Actheres, Trachelastes, Brachiella, Lernoceros, Anchorella.

III. ONCHUNA. Attachment by hooks at the free extremities of the first pair of thoracic limbs. Gen. Diechelestium, Lamproglenis, Ergasilus, Nicothoe.]

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1 They constitute the class Turbellaria of Ehrenberg, and a synopsis of his arrangement is given in Lam. Anis. sous Vert., 2de ed. vol. iii. p. 609. [As to this class the reader may consult Oersted's Planktonworm, 1844; Memoirs by Quatrefages in the Ann. des Sciences Nat., and Schmidt's Neue Wielbelloise Thiere, vol. i. 1859.] 2 See a description of some British species by Dr Johnston in the Magazine of Zoology and Botany, vol. i. p. 529. 3 Editor. Syn. p. 596. The Echinodermata have been defined to be radiated animals, with a coriaceous or crustaceous skin, commonly tuberculated, or even spiny, and perforated with holes arranged in regular series, whence issue contractile tentacular suckers. The mouth is either inferior or lateral, and mostly armed with certain ossaceous pieces that form a circle of teeth within the lip; the stomach is a loose bag, with distinct parietes, and with an intestine or cecal appendages; the respiratory apparatus is vascular; and the species are oviparous. This definition, however, must not be too nicely examined, otherwise several animals, which offer but a feeble and partial admiration of its characters, might be excluded from a class to which they properly belong. The stellated disposition of the organs is generally so remarkable, that fancy will dream the Echinodermata to be the children of night, which have drawn their figures from the stars that presided over their birth; but there are among them some vermiform families which have resisted the planetary influence, excepting only in certain parts around the mouth. Their next most general character is derived from the tentacular tubes which the animals push out from pores drilled in rows between the vertical segments of the thick integument of the body, and withdraw again in part at pleasure; but the character becomes abnormal in some Holothuridae, which have these suckers pululating irregularly from the surface; and it fails altogether in Sipunculus and its allies. The organs in question much resemble the tentacula of the snail, but they are really very dissimilar both in the use and mechanism of their movements: they may be compared to the glass of a thermometer, for they are closed tubes, with a vesicular bulb placed within the body, and they are protruded by forcing the fluid, with which the bulb is filled, up the cylindrical portion. It is not through them, as Lamarck imagined, that the circumfluent water gains access within the body, although it is very true that almost all the Echinodermata contain a large but variable quantity of it, partly flowing through a special apparatus, and partly effused, if we may so speak, into the visceral cavity, bathing the surface of every viscus which may be said to float in it; and since the quantity of this water can be increased or lessened at pleasure, so we find that the contour of all the flexible species is liable to alteration of figure, according to circumstances.

When "Batt'ning in ease, and slumbering life away," the skin is rounded and swollen, and the organs are distended and displayed; but if alarmed or removed from their sites, the fluid escapes from them, and colapsion and retraction follows. Other purposes which this water must serve, are its aid in rendering the crude nutritive fluids of digestion fit for assimilation, and its purifying influence over the blood; for we learn from Delle Chiage, that in all the Echinodermata there is a blood of a yellowish or orange colour, composed of a large proportion of lymph, and a certain number of globules endowed with a self-rotatory motion. In what course this blood circulates has not been determined. Tiedemann, who may be regarded as our best authority on such a point, says that it "moves in a circle, but which is confined to the alimentary sac and ovaria alone. In the Asterias, numerous thin-coated veins, coming from the stomach, the cecal appendages, and ovaries, unite into a single trunk. This produces a dilatation analogous to a heart, and then ramifies like an artery. In sea-hedgehogs are found, on both sides of the circumvolutions of the intestinal canal, two vascular trunks, the external of which seems to be a vein, and the internal an artery. These two trunks communicate by a dilatation similar to a heart, or by their minutest ramifications. The intestinal canal of Holothuria likewise exhibits an arterial and venous trunk, connected with each other by their smallest ramifications, as well as by a large vascular net-work spread over one branch of the respiratory organ." Delle Chiage's description of the same system differs considerably; and it is difficult to define the limits between it and the system of vessels for conveying currents of water through the body. Blainville, of distinguished excellence as a comparative anatomist, felt this difficulty. He has concluded that there is no real circulation, and that the sanguineous system of the Asterias, and perhaps even of the Echinida, is nothing else than a system of ramose aqueducts, like the trachea of insects; and indeed it appears certain that these vessels communicate with the exterior by orifices more or less conspicuous. But, he adds, it is difficult to say as much of the vessels which we find in the Holothuridae, for no anatomist has suspected their direct communication either with the arbuscular tentacula, or with the real aquiferous vessels, or with the dendroidal branchiae; so that in these animals there may be an oscillatory movement of the blood in its special system, but certainly no circulation of it, returning and going to and from a font of pulsion.

The aquiferous system alluded to must not be confounded with the aquiferous cutaneous tubes that jut out from between the tubercles on the dorsal surface of the star-fishes, but is an internal ramose set of vessels for leading water from the general cavity of the viscera, more especially into the locomotive organs of the animal, and its buccal tentacula. "It is composed of vessels," says Tiedemann, "which commence from a canal placed around the mouth, and spread in rays over the internal surface of the skin, as in Holothuria, or proceed to the chalky covering, as in sea-hedgehogs and asterias. These vessels open in the hollow tentacula, and their vesicular dilatations. They contain a limpid fluid, which is shed over the tentacula during the animal's motions, and causes their increase or shrinking. When the animal draws in his tentacula, the contraction of their muscular coats forces the liquid again into the vessels. The fluid contained in this vascular system is not therefore agitated by a circular movement, but only flows outwards from within, and vice versa. This fluid, which is probably derived from the blood, seems at the same time to serve for the nutrition of the skin, of the chalky covering, and the locomotive organs."

With this system, that of respiration is most intimately associated; nor indeed are there any separated branchiae, either in the star-fish or sea-eggs, whose fluids are aerated by a flow of pure water over their surfaces, and around and within their viscera, driven over them in currents determined by the regulated action of vibratile cilia, which clothe them almost everywhere, as the researches of Dr Sharpey have more especially proved. In the Holothuridae, anatomists have generally considered as pulmonic certain organs which lie between the long curves of the intestine, and closely connected with it. They are very much branched in a dendroidal fashion in some species, their branches reuniting successively backwards, until they form at last two trunks, or one only, that opens with the intestine into the cloacaum; but it seems to show how readily their presumed function can be transferred to the general cavities when we find other species of the family in which these organs are slightly sketched, and some in which their existence is not to be demonstrated.

Lamarck divided this class into three sections or orders:

1. Fistulida. Body elongate, cylindraceous; the skin leathery, soft, and irritable; intestine with an oral and anal orifice, the former encircled with retractile tentacula.

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1 From lyon, a hedgehog, and Nema, the skin. 2 Plainville's Man d'Actinologie, p. 65. 3 Ibid. p. 86. 4 The feet or suckers are here meant. 5 Cyclop. of Anat. and Phys., art. "Cilia," i. p. 615. II. Echinida. Body more or less retund or angular, covered with a shell of immovable testaceous pieces without projecting arms; anus distinct from the mouth.

III. Stelliferida. Body depressed, circular or angulated, and divided into arms or rays; the skin creto-coriaceous, tubercular; intestine in some families only, with an orifice distinct from the mouth.

[Professor E. Forbes proposed this arrangement of the Echino- dermata in his History of British Star-Fishes (1841).]

Order I. Pinnigera. Chinoidea. First appearance of cirri springing from branchial membranes, which with the true arms form the organs of motion.

II. Spinigera. Ophiuridea. Disappearance of branchial mem- branes; cirri as before; true arms clothed with spines for motility.

III. Cirrigera. Asteroidea. Arms disappear; body more or less lobed, and lobes channeled beneath for cirri, which act as suckers, and are the organs of motion.

IV. Cirri-Spinigera. Echinidea. Gradual disappearance of lobes; cirriferous canals appearing as avenues where cirri act, as in Order III.; but are assisted by mobile spines clothing the integument.

V. Cirri-Vermigera. Holothuriidea. Lobes disappear; motion effected by avenues of cirri, assisted by contraction and extension of the soft body.

VI. Vermigera. Sipunculidea. Cirri become obsolete and disappear; motion effected by the contraction and extension of the animal's body.]

Order I.—Fistulida, Lamarck.

(Holothuridea—Holothuracea.)

The radiant character of the class is faintly impressed upon this family, being marked with decision only in those parts which encircle the mouth. The form of the body is in general that of an elongated cylinder or pentagon, rather unseemly, and invested with a thick coriaceous tunic, which is sometimes scaly, like the skin of a fish, more frequently of a uniform earthy colour, or white painted with bright red or orange spots. If placed in a vessel of sea-water, we soon observe, issuing from perforations in the skin, a number of papillary tubes, which the animal has the power of extending at will. These are scattered over the body, or more usually arranged in rows, limited sometimes in extent, at other times running uninterruptedly from one extremity to the other. The creature gives perhaps little other evidence of life than what we infer from the protrusion of these organs, and from continual changes in the figure of its body. A species of Holothuria, which we watched for some time, was as changeable in this particular as its native ocean. From a long vermiciform cylinder, it would become gradually shortened, and swollen in the centre; then it would relax itself, and again become cylindrical; next one part would be blown out, and another drawn in, with a deep stricture, as if a thread had been tied round; or the contraction would begin near the head, which is then made very narrow, and would spread backwards, the anterior portion recovering its original diameter as the wave of constric- tion passed away; and sometimes the contraction will spread in the opposite direction. This mutability in form is dependent on the action of the muscles which enter into the composition of the skin, and which are of two kinds; one set forms a series of transverse parallel fibres, lining its inner surface completely with an even muscular coat, while the other set is collected into five or ten strong cord-like ten- dinous bands, which stretch from the oral to the anal aperture, usually in pairs, but where five only, they are at equal distances.

In this state, it is not always easy to say which is the anterior and which the posterior extremity, for the tenta- cula and foreskin containing the oral apparatus are retractile, and then wholly concealed. When displayed, the tenta-

1 "Quaeque Janturae in Echinis quasi analogia est, nisi quod amplior sit, et dentes deficient, quibus ea in Echinis armata repertur." Pallas, Micr. Zool., p. 156.

2 De Anim. Marin., p. 86.

Echinoderma the other viscera, through the mouth or anus; do, in fact, voluntarily, and from a law of their nature, evicerate themselves. The fact on which this seemingly absurd conjecture is based is most singular, perhaps unexampled in any other animals. When a Holothuria is placed in a basin of sea-water, it has been seen to emit jets of water from the posterior aperture at regular intervals, the jets succeeding each other at not more than about a minute's interval. This water is undoubtedly what has been rendered injurious by its stay and use in respiration, mixed probably with a considerable proportion from the intestine. But when the water in the basin has become impure, these jets become also less regular; and after evidence of uneasiness, and some unusual motions, the worm will at length vomit up its tentacula, its oral apparatus, its intestine entire and with its appendages, and a large cluster, if not the whole, of the ovaries. And after this complete embowelling, the animal lives for at least six or seven hours; for the empty skin shows, by its motions, that nearly all its irritability remains, and even its power of locomotion is not lost.

"Denique, quod magis mirum est, omnia Hydrea individua, postquam intestina sua dejecere, septem et ultra horas supervivunt, motu non duntaxat elasto, sed progressivo gaudientia." Sir John G. Dalyell has even proved, by actual experiment, that if this poor embowelled worm is supplied with fresh sea-water at proper intervals it will live to replace all its viscera with new growths, reproduce new tentacula, new teeth, a new stomach and intestine, and all its complicated aquiferous system, so as to be in every respect as it was previous to its wonderful evomition. It is by such miracles that we are brought to exclaim with Pliny, "mibi constentu sese persusit rerum natura, nihil incredibile existimare de ca."

The Fistulidae are natives of every sea. Blainville believes them to be more numerous on the coasts of cold or temperate countries than under or within the tropics; but the data for such an opinion are unsatisfactory. They abound in the Mediterranean, and are scattered over the German Ocean. The more remarkable species live at considerable depths, and come rarely under the notice of the zoologists; but some are littoral, lurking among sea-weed and in the crevices of rocks, while others burrow in the sand. They appear to be gregarious, and are evidently by their organisation very limited in their powers of locomotion. When they reluctantly remove from their sites, it is by the aid of their tentacular suckers; thrusting these forward to the utmost, they fix them to the ground, and drag the body on at a pace slower than the shadow on the dial. By the same organs they retain themselves in their natural positions, and effect a safe anchorage when the sea is agitated to the bottom. Otho Fabricius says of Holothuria pentactes, that it can swim, a sort of exercise which the structure of the creature would not lead us to predicate; but the fact appears to be confirmed by Bosc, who tells us that the Holothuriae swim slowly, as much by a kind of vermicular motion as by that of their tentacula, and the faculty which they possess of inflating the body at will.

We learn from Delle Chiase, that some of the Holothuriae are eaten by the poor inhabitants of the rich shores of Naples; and the Sipunculus edulis (Lumbricus edulis, Pallas) serves as food for the Chinese who inhabit Java, and who search for it in the sand, with little bamboo sticks prepared for the purpose. Their appearance is to us loathly, and they breathe no Sabean odour; yet the celebrity of the Trepang, a species of Holothuria, must rescue the family from contempt in the eye of every liberal Echinoderme, who, rising above national prejudices, allows his Chinese brothers to extol unchecked their treasures of the stormy seas. "This animal," says Professor Jameson, "is used very extensively by the Chinese for culinary purposes. They make of it a very rich and palatable soup, and dress it in different kinds of stews. There are various modes of curing it. It is first gutted and the water pressed out of it, and then laid in dry lime, called by the natives chunam; afterwards, according to the circumstances of the fishing station, dried in the sun, or on stages by means of fires of wood under them. It is a most important article of commerce, and is the most considerable article of the exports of the Indian islands to China, unless, perhaps, pepper. There are fisheries, as they are called, of trepang, in every country of the Indian Archipelago, from Sumatra to New Guinea. It has also within these last few years been discovered abundantly on the coasts of Ceylon and the Isle of France, and is no doubt general throughout those seas. It has, as we are informed, already been sent from thence to China, where it finds a ready market, although, from its being unskilfully prepared, it is classed with the lowest qualities of the Archipelago. When the Chinese can be employed in fishing and preparing it, there is little doubt that it will form an important article in the commerce of those countries with China, as it can be got in any quantities."

After some farther details relative to the mode of fishing and curing it, the professor adds, "the whole quantity sent to China from Macassar, and other parts of India, may be estimated at 14,000 peculs. Taking this quantity at the low average of forty dollars a pecul, and valuing the dollar at 4s. 3d., its entire value, in a commercial view, is Ll.119,000. Notwithstanding this enormous export to China, we do not understand that its value in the market has ever been materially affected by the quantity imported; an evident proof that the demand of the market still exceeds the supply. When we reflect that the opium, pepper, birds' nests, sharks' fins, trepang, and various other articles, the products of the countries under our control, are fully as indispensable to the Chinese as the teas of China are to Europe, the fear so much entertained of the Chinese interdicting our trade with that empire is quite preposterous. In short, these few articles of luxury give us the command of the Chinese tea market. The celestial empire cannot exist without its trepang and birds' nests."

The systematic arrangement of the order has kept increasing in complexity with the discovery of new species, and their minute examination. Linnaeus found two genera sufficient in his time, viz., "Sipunculus—corpus teres, rostro cylindrico angustato;" and "Holothuria—corpus ore antico, tentaculis carnosis antice cinctum." Pallas referred the latter to Actinia, of which they formed a section, distinguished by having two apertures to the alimentary canal; for it was the opinion of this great naturalist that differences of structure, which, in higher grades of animals were justly reckoned to be of generic value, were in worms to be deemed not more than specific. The family, nearly as we view it, was first defined by Lamarck, who made it embrace five genera, that stood in three separate sections thus:

1. Actinia: 2. Holothuria: 3. Fistularia: 4. Priapulus: 5. Sipunculus.

In the Regne Animal, the Echinodermata form two orders, the pedaceous and the apodous. The Holothuries are one of the families of the first, while the species which Lamarck would have referred to his third section constitute the entire second order. Cuvier throws the Holothuries into unnamed groups, from peculiarities in the distribution of the tentacular suckers; and his apodous genera

Echinodermae Molpadia, Minyans, Prapulans, Lithodermes, Siponculus, Bonella, and Thalassema. The latter is now generally allowed to belong of right to the class Vermes.

Latreille's arrangement is little other than the reduction of Cuvier's named divisions, as will appear from the following outline of it.

CLASS—HOLOTHURIDA.

Order I.—APODA.

Fam. 1. Lombriformis. Mouth unarmed. Genera—Bonellia, Siponculus, Minyans.

2. Veretiformis. Mouth armed with osseous pieces—Prapulans, Molpadia.

Order 2.—POLYPODA.

Fam. 1. Vespipedes. Feet scattered over the whole body. Genera—Holothuria, Actinopoda, Fistularia.

2. Inferipedes. Feet ventral only.—Phantapus, Phallidus.

Blainville's method of classifying the proper or pedunculate Holothuridae is exhibited in this neat synoptical table:

| Body | Suckers underneat... | Cucumaria | |------|---------------------|-----------| | | subprismatic, with inferior suckers... | Holothuria | | | fusiform, with scattered suckers... | Thyone | | | vermiform, with pinnate tentacles... | Fistularia | | | subpentagonal, with suckers in ambulacra... | Cucumaria |

But the host of species discovered within these few years, during the voyages undertaken for the promotion of the natural sciences, has proved the inadequacy of these systems; and although the researches of Jaeger and Brandt, with ample materials at their disposal, have brought into operation characters of a higher value on which to found a better arrangement, that good work has not yet been satisfactorily accomplished. The characters on which the naturalists mentioned have proposed to proceed, are derived from the absence or presence of the tentacular suckers, their homologous structure or dissimilarity, the existence or not of the aquiferous branchial apparatus, the pattern after which the suckers are disposed, the floating character or adhesion of the respiratory organ, and lastly, the variations in the tentacula which guard the mouth. Guided by these characters, whose importance is in the order stated, Brandt has worked out a genealogy of the family, perplexing from its numerous subdivisions; but it is confessedly the basis of that lately offered to us by Blainville, and which we now analyse; for, however dry and barren such tables may seem to be, it is really from their careful study that the student obtains his clearest view of the forms and general structure of the species. "The use of synoptical tables in every branch of science," says Mr. Duncan, "is obvious. They afford great aid to memory; but also, on frequent review, they suggest continually to the inquiring mind new traces of undiscovered relations." Blainville's new method of distributing the species, then, is as follows:

A. II: VERMIFORMES.

Body elongate, soft, vermiform; the feet small or none.

No suckers; tentacula pinnate...1. Synapta, Escholtz.

No suckers; tentacula pinnatifid...2. Chirodota, Escholtz.

Suckers small, in five bands...3. Oncinolabes, Brandt.

These species are closely connected with the apodous Entomoza by the Siponculus, the Prapulans, and perhaps even the Molpadia. Their tentacula are continually in motion, moving towards the mouth. There is no cloaca, the anus being strictly terminal; and there is no aquiferous respiratory dendroidal apparatus.

B. II: ASCIDIFORMES.

Body short, coriaceous, convex above, flattened below, with the orifice superior rather than terminal.

The skin scaly...4. Cuvimria, Peron.

The skin rugose but soft...5. Prolus, Oken.

C. II: VERETILLIFORMES.

Body considerably elongated, softish, subcylindrical, covered throughout with tentacular suckers, of which the inferior are the longest.

The anus widely patentulous...6. Holothuria.

The anus plaited...7. Bohadichia, Jaeger.

The anus closed, with five teeth or scales...8. Mulleria, Jaeger.

D. II:

Body more or less elongated; the inferior tentacular feet longer than the superior, and disposed in a determinate number of longitudinal rows.

The suckers in three rows...9. Stichopus, Brandt.

The suckers in five rows...10. Diploperideris, Brandt.

E. II: CUCUMIFORMES.

Body but little elongated, more or less fusiform, pentagonal, with the tentacular feet forming five ambulacra, one along each angle.

The feet small or obsolete...11. Lissocoma, Brandt.

The feet very obvious, and tentacula pinnate...12. Cladodactylus, Brandt.

And tentacula pinnatifid...13. Dactyloa, Brandt.

The species in this section connect the family with the Echinidae.

F. II: SIPONULIFORMES.

Body more or less suddenly narrowed behind, the pentagonal figure indistinct, without ambulacra, and perhaps without tentacular feet; tentacula simple, short, and cylindrical, as in Actinia.

Embraces only the genus...14. Molpadia, Cuvier.

[Professor E. Forbes, in the work already cited, thus arranges the British genera of Holothuriidae:]

Fam. 1.—PENTACTADAE.

Suckers in five regular rows; body angular. Cucumaria, Bl. (Pentacta, Ag.) Suckers alternate in each row, closely set; tentacles 10; dental apparatus composed of nearly square plates. No gizzard.

Ocnus, Forbes. Distant suckers on the angles; tentacles 10; dental apparatus very short; no gizzard.

Proclus, Forbes. Distant suckers, those below always bent; tentacles 10; dental apparatus short, truncate; no gizzard.

Fam. 2.—THYONIDAE.

Suckers scattered over the whole body, which is cylindrical. Thyone, Oken. Tentacles 10; dental apparatus with 10 appendages directed downwards; genital tubes simple.

Taygonidium, Duben and Koren. (Cucumaria communis, Forbes.) Suckers with a tendency to form 5 rows; tentacles 10, in pairs; dental apparatus with 10 appendages, directed upwards; genital tubes divided.

Holothuria, L. Suckers few above and in the form of conical papillae; very numerous below, and extending on a sort of disk from one extremity of the body to the other; tentacles 20; the spines peltato-ramose; genital tubes branched.

Fam. 3.—PSOLIDAE.

Suckers in 3 rows on an oblong disk, occupying a part of the under side of the body; 2 additional rudimentary rows of suckers.

Prolus, Oken. Body irregular; tentacles 10.

Fam. 4.—SYNAPTIDAE.

Suckers absent.

Synapta, Auct.—(Chirodota, Forbes). Skin furnished with oval perforated calcareous plates and anchor-like bodies of microscopic size.

The same author arranges the British Siponulidae thus:

9 Proboscis with a circle of tentacles at the extremity, and the vent at the base.

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1 Rhynce Anima, iii, pp. 233 and 241. 2 Man. d'Actinologie, p. 191. 3 Man. d'Actin. Supp., p. 650. 4 The species described by Forbes proves to be a Synapta, not Chirodota. See Woodward and Barrett's paper "On the genus Synapta" in Proc. Zool. Soc. 1858. Chirodota is distinguished by having wheel-like plates in the skin, without anchors. In Steenstrup's genus Myriostoma, the wheels are larger and scattered over the skin, each having its own stalk. The calcareous bodies found in the skin of the Synaptidae are very interesting objects for the microscope. Order 2.—Echinida.

The Echinidae are popularly known by the name of sea-urchins or sea-hedgehogs, given to them from their shells being covered with moveable prickles like the skin of those quadrupeds; "Horret capillis ut marinus asperis Echinus;" but when the prickles have fallen off, the shells are more commonly called sea-eggs, partly from a conformity in the figure between the objects compared, and more so from a similarity in their calcareous composition and texture. From their forms, certain genera have been also called turbans, diadems, mermaids' skulls or hearts, or fairy-stones; a nomenclature more pleasing to us than the Greek compounds of science, and not more poetical than useful, since it aptly conveys a portraiture of those varieties in which Nature has, with her usual sportiveness, moulded these productions. It is from this variety that a general description of the shell becomes impossible; and to form a correct idea of its beautiful and complicated mechanism, it is necessary to select one as a type or standard for comparison and further description. For this purpose we shall take the shell of the common Echinus (E. esculentus).

The shell is of a globular figure, with a flattened base, formed of ten conformable plates, alternately broad and narrow, and ten annectant ones dissimilar in character. All of them proceed from the rim of the oral aperture in the base, and rise upwards, bellying in the middle, whence they again converge, and are united in a circle opposite the mouth by a series of small pieces to be afterwards described. The first series of plates is called areae by Linnaeus; and those by which they are joined together, and which are all narrow and of the same size, he named the ambulacra, from a resemblance his rich fancy traced in them to the walks between the parterres of a garden laid out after the olden fashion. The areae are thickly studded with tubercles of different sizes; and when more narrowly examined, it will be seen that each area is divided down the middle, by a zigzag line, into two equal halves, composed of numerous small pentagons set in cross rows, and dove-tailed into each other with the most perfect adaptation, the projecting angle of one series being fitted into the concave angles of the other. Their tubercles support the spines, which move on a pearly globular pivot that sinks into a corresponding cup in the base of the spine, and where they are retained by the soft epidermis or skin that covers the entire shell in its fresh condition. The spines are calcareous, columnar, very often large in proportion to the shell; but with these primary spines smaller ones of three kinds are numerously intermixed, viz. one of the same form, differing only in size; another slender as a hair, but dilated into a club at each end; and another on a flexible stalk supporting three moveable prongs placed in a triangle, not very unlike the trident of Neptune. These Müller mistook for parasitical Echinodermata; and we still find them in many systems forming the genus Pedicellaria among these animals. Their function is unknown; for Monro's conjecture that they supply the place of the organs of the senses in the more perfect animals is a very loose one, and improbable.1 The ambulacra are joined to the areae by a plain or even suture, and instead of being tubercled, they are perforated from top to bottom with holes, always disposed after a regular pattern, which probably varies in every species. These holes give exit to numerous fleshy tubular pedicles, whose apex forms a circular testaceous shield, serrulated round the rim, concave and perforated in the centre, and formed of six distinct pieces, united by a plain elevated suture. If we now examine the top of the shell, we find it occupied by a small circular tuberculated plate, with a hole in its centre (the rent), and the plate surrounded by five triangular scales, and five less ones of a lunate figure placed exterior to and between them. The triangular scales, called the ovarial, by Mr Gray, are each of them perforated with a hole leading to the ovaries, and they stand opposite the large areae, into an emargination of which the point of the triangle dips; while the lunate scales, the interovarial pieces of Mr Gray, embrace the points of the small areae, and the ambulacra, and are likewise perforated with a hole scarcely visible to the unaided eye, and the use of which is quite unknown.2 One of the ovarial plates is considerably larger than the rest, convex externally, and perforated like a sieve with numerous minute foramina, and internally thick and rugose. This plate is somewhat similar, both in form and perhaps in use, to the orbicular spot on the back of the Stellerida, called corpus spongiosum by Spix.3

This description of the crust or shell of the Echinides, it will be remembered, is in a great degree specific, and will not apply universally even to the globose species, from which it is especially drawn; and it must less accurately apply to those which are greatly depressed, or oval, or heart-shaped, or cranial, or which rise up in the form of a conical pentagon. In all these the ambulacra are often only half of the typical number, and often only partial in their extent; while the areae become coalescent, amalgamating more or less completely, with a consequent loss in the distinctness of their radiation. In many of these, also, the oral aperture loses its central position, and gradually, through a succession of genera, approaches the margin, which in some it occupies; the vent being subjected in its position to the like variations, and drawing with these, alterations of equal extent in the other exterior apertures. Nor in shape and armature does the mouth vary less. It is circular in the true Echinus, and armed within with a most complex apparatus of calcareous jaws, arches, and teeth, consisting of twenty-five separate pieces; while other genera, nearly allied, present the strange contrast of having no trace of these parts, being wholly toothless, with the outer aperture transformed into a narrow transverse labiatus slit. To fill up the interval between these extremes, there are genera which have an oral apparatus less complicated than that of the Echinus; for in natural orders of families there are no abrupt transitions in structural organization. Amid all their varieties there reigns an evident connection and harmony, indicating a design or plan after which they have been called into existence; and in contemplating that unity of purpose, and the beauty and intricacy of the workmanship bestowed on the individuals created to fulfil that purpose, we endow them with our superior intelligence, and give

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1 It has been recently stated that the animal uses them as grappling irons to attach itself to sea-weeds. Our native species covers itself, when residing between tide-marks, with fragments of sea-weeds, evidently as a means of concealment; and we believe they are held on the shell by means of these organs, which are a sort of self-acting forceps.

2 Gray in Annals of Philosophy, n.s., vol. x. p. 425. On the structure of the shell see also Grant's Outlines of Comparative Anatomy, pp. 18-21. utterance to their evidence of the existence and attributes of the Deity.

From the differences just indicated in the structure of the mouth, we naturally and correctly infer that there will be a corresponding diversity of the food on which the Echinida subsist. The jawless Spatangi burrow in the sand, and, swallowing the earth around them, extract a hard nutriment from the decayed animal and vegetable matter intermixed; but the Echini live amid rocks near low water, trace their crevices, and there seek the small crustaceous and testaceous Mollusca, whose shells they are enabled to break by the power and hardness of their teeth. Cavolini indeed asserts that the Echini live upon sea-weed; but the testimony of Dr Monro to the contrary is equally positive, and more consistent with the anatomical structure. That great anatomist tells us that they prey upon living Buccina, "as I had found particles of shells in their alimentary canal;" and they seize and secure their prey by means of the suctorial tubes which garnish the ambulacra. "I therefore directed the fishermen to bring me, along with the Echini, some living Buccina; to which, as I had supposed they would do, they attached themselves so effectually, that when I lifted the Echinus out of the water, I found it could support with ease a Buccinum which weighed nearly a quarter of a pound."1 "The Echinidans," says Mr Kirby, "whose station appears to be often near the shore, upon submerged ledges of rocks, feed upon whatever animal they can seize. We have seen that they sometimes turn upon their back and sides, as well as move horizontally. This enables them more readily to secure their food, with the aid of the numerous suckers in the vicinity of their mouth, which, when once they are fixed, never let go their hold till the animal is brought within the action of their powerful jaws. Lamarck thinks they do not masticate, but only lacerate their food; but as two faces of each of their pyramidal organs answer those of the two adjoining ones, and these faces are finely and transversely furrowed, this looks like masticating surfaces. Bosc, who appears to have seen them take their food, says it consists principally of young shell-fish and small crustaceous animals. As the latter are very alert in their motions, it is difficult for the sea-urchins to lay hold of them; but when once one of these animals suffers itself to be touched by one or two of the tentacles of its enemy, it is soon seized by a great number of others, and immediately carried towards the mouth, the apparatus of which developing itself, soon reduces it to a pulp."2

The intestinal canal which this food has to traverse is, like that of the Fistulida, long, cylindrical, and tortuous, with a vent separate from the mouth. There is no chylopoetic viscera; but Blainville deems to be hepatic some glandular spots which he has detected in the parietes of that portion which may be regarded as stomach.3 The intestine is fringed throughout with a mesentery, on the under edge of which Monro found two vessels without valves, nearly equal in size and parallel to each other, which he injected with quicksilver, and from them filled a beautiful network of vessels, not only on the intestines, but dispersed on fine membranes, which tie the intestine to the inner side of the shell. "I could not, however," he continues, "observe that these two vessels communicated with each other directly, nor by the medium of any organ like to our heart, nor could I observe in the living animal any beating organ like to the heart; yet near to the anus,

and connected to the rectum, which is the place of the Echinoderma heart in many other worms, I found a small organ, which seems to be hollow. It appears to be highly probable that one of these vessels is the principal artery or aorta, and the other analogous to our vena cava; and that they communicate by invisible branches, and circulate the blood by the muscular action of their coats, without the intervention of a heart, nearly in the way the vessels in fishes carry the blood from the gills back to their heart."4 Blainville, however, with a full knowledge of Monro's opinions, and of subsequent discoveries, aided too by his own dissections, acknowledges that he cannot tell which vessels are arterial and which venous, and thinks it very possible that there is no such distinction in animals so low in organisation as the Echinida, the vessels being at one and the same time both arteries and veins.5 How the blood circulates is therefore a subject of conjecture; but we know more precisely the manner in which it is aerated. Lying along the inner surface of each of the ambulacra, there is a branchial leaf or doubled membrane, "not unlike the processes or subdivisions of the gills of a skate," and having a direct communication with the external tubular suckers, already described as pulsulating from the ambulacral pores. The water sucked in by these tubes gains access within the shell by two of the pores (for there is a pair to each sucker), and by their divergence is carried into the opposite folds of the branchiae. Here one portion of the sea-water is supposed to be exuded into the general cavity of the shell, between its inner covering and the intestine; while another portion is again collected, by anastomosing vessels, into five large ducts, that terminate, each by two branches, in large sacs or receptacles over the sockets of the teeth, communicating with each other; and from these the liquor passes down the sockets of the teeth, and is discharged into the sea, on each side of the tooth, between the socket of the tooth and beginning of the oesophagus.6 Such is the course of the fluid as described by Monro; but later anatomists maintain that the current has in fact exactly the reverse direction; and they inform us that the sea-water which fills the interior cavity is introduced through certain membranous tubes, arranged in ten small groups round the oral aperture in the base of the shell. Be the fact as it may, there remains a provision of aqueducts most curiously contrived for conducting the medium of respiration and assimilation through the body; and very probably the current is propelled and directed in its way by the action of vibratile cilia, which in these animals, as in most others, clothe all the serous surfaces of the internal viscera, keeping the fluid in contact with them in perpetual change and renewal, and not allowing it to stagnate even on the outer shell.7

The ovary or roc occupies much space within the shell, being very large in proportion to the animal and its other viscera. It is divided into five or four lobes, disposed radiately, each lobe having a distinct exterior aperture, as well as a communication with each other. The apertures are placed round the anal when this is central, but otherwise their relationship is not so regular and constant. It is probable the ova, after their extrusion, undergo no change analogous to a metamorphosis.8 We have examined the young of Echinus esculentus when it did not exceed one-eighth of an inch in diameter, and then it had the form and armature of adulthood; but the prickles were toothed along their sides, and the forcipated organs appeared to have only two prongs. The pieces of which the shell was

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1 Bridgewater Treatise, i. p. 210. 2 The Struct. and Physiol. of Fishes, p. 67. 3 Mon. d'Actinologie, p. 72. 4 Mon. d'Actinologie, p. 78. 5 See Sharples in Cyclop. of Anat. and Phys. i. p. 617. 6 Monro's Struct. and Physiol. of Fishes, p. 69. 7 Ehrenberg says that the prickles of Echinus esculentus are covered with these cilia. 8 Ann. des Sc. Nat. n. s. iv. p. 304. 9 It has been usually believed that the Echinida were hermaphrodites, but M. Edwards and Dr Peters are said to have discovered that they are of separate sexes. 10 Ann. and Mag. of Nat. Hist. vol. i. p. 156. In some species there are found individuals presenting even a pyramidal shape, and this takes place when there is still formed a great number of plates subsequently to the consolidation of those occupying the greater diameter of the animal's body. These facts sufficiently explain the gradual growth of beings which approximate more or less nearly to the spherical form; and show how carefully we should guard against the introduction of nominal species in consequence of a mere difference of form resulting from age only.

It would be interesting to trace the development of these animals ab ovo. But no naturalist has yet observed the state of the Echini on their first issuing from the egg. As to the spines, it is evident, especially in the Cidarites, that those surrounding the mouth are the first that attain their full growth, while the largest are those in the upper tier of the disc; and those which have not yet completed their growth are found around the oviducal plates on the outside. The correctness of these observations will be demonstrated by comparing the differences of development exhibited in this region by the spines that stand nearest to each other. We should be mistaken, however, as to the growth of the Echinodermata, did we think that there is a generic connection between the plates, on account of their forming vertical series from the mouth to the summit of the disc. It has been already remarked, that the plates of each space are alternately a little more elevated than each other; but no attention has been paid to the manner in which the plates of all the spaces succeed each other in the same Echini; and yet, if we consider it closely, we shall see that the new plates are developed in spiral lines, passing without interruption from one series to another, through all the spaces from the circumference of the mouth to the dorsal summit, so that those which rest on each other in a vertical line do not make their appearance in immediate succession. It appears to me well worthy of remark, that in these animals, holding so low a rank among organized beings, we should find the succession of the solid parts composing the integument so strikingly analogous to the arrangement of the leaves around the stems of plants; an arrangement the laws of which have been recently discovered by M. Schimper, and explained, so far as regards the Coniferae, in a memoir of M. Braun on the arrangement of the scales of their cones.

The small plates surrounding the mouth, and those around the anus, are arranged in a peculiar manner. They are easily moved, and thus facilitate the deglutition of the food, and the voiding of the excrements. In general the testa of the Echini are not so immoveable as one who had not observed them in a fresh state might be led to suppose. All the plates forming the upper part of the disc are often set in motion; sometimes they sink, sometimes they rise, and, in the oblong species, the longitudinal diameter is often extended beyond its ordinary length.

The Echini are in general littoral animals. The species with a thin brittle shell, covered with small hairs like bristles, as the Spatangi, burrow in the sand, covering themselves up by the aid of their spines; but those with a stronger prickly crust hide themselves in rocky places. Looking at their rotund limbless forms, we might imagine that they must constantly be fixed to one spot, or, if moveable, that from the difficulty in bringing members so numerous and opposite to co-operate, or from hesitation in what tract to move, seeing that they are all alike and look to all sides, still a perpetual sedentariness would be their choice. But it is not so, and their motions are neither less regulated nor slower than those of the majority of invertebrate animals. They usually advance on their flat basis, but when an individual chooses, it can move forward by turning on

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1 Agassiz in Annals of Nat. Hist. i. pp. 40-42. Echinoder- itself like the wheel of a coach. From the nature of their localities, they are much exposed to bruises, and worse foes in the shape of fish and worm. The latter they repel by their spinous panoply, which they can erect and stiffen, presenting a thousand spears on every side, and no point unguarded; the bruises they bear with impunity, and it must be a wound only short of total disorganization from which they cannot recover. Monro has even seen the pieces of a broken shell walk off in different directions.

By what organs the Echinida exercise their locomotive powers has been disputed. Most authors assign this duty to the spines of the areae and the ambulacral suckers conjointly. Baster tells us, that the latter are the principal organs; and according to Blumenbach they are the only ones, the prickles being merely organs of offence and defense. Now, says M. Agassiz, this is a very erroneous opinion—vox et praterca nihil—for it owes its birth and continuance to a mere verbal influence, the term ambulacra being first translated into alleys or walks, and then the organs which grow in them were subsequently supposed to be the walkers. Without questioning this very questionable transition, we know that Agassiz is wrong in denying the tentacula their pedesitrous function. "How, in fact," he asks, "could these small tentacula, with all their softness of texture, situated, as they generally are, in that part of the body which is never brought into contact with the ground when the animal moves, and overhung by calcareous solid spines; how, I ask, could those flexible tubes be used as organs of motion? It is an undeniable fact, and I have often observed it myself, that it is with their spines the Echini move themselves, seize their prey, and bring it to their mouths, by turning the rays of their lower edge in different directions." Our own observations, on the contrary, have satisfied us that the common Echinus moves from place to place solely by the aid of the tentacular suckers; the spines, as Mr Couch correctly states, acting as levers or crutches. Agassiz exaggerates the littleness and weakness of the suckers; in the common Echinus, whose spines are not above half an inch in length, the suckers can be extended one inch and a half, so as greatly to overreach the spines; and they can at the same time be rendered firm and rigid by distention, from water, and the contraction of their own muscular parietes. The spines are moved principally, we think, by means of the exterior irritable skin which covers the shell and envelopes their basis; but when these spines are very large, the tubercle to which they are articulated is perforated for the transmission of muscular fibres from within, and which appear to be inserted into their roots by a coronet of fibres. The number of spines and suckers—and let it be remembered that there are several muscles to every spine and every sucker—on a single individual is indeed wonderful. A specimen of *Echinus esculentus*, of moderate size, will have at least 160 primary prickles on each of the large, and 80 on each of the small areae; that is, 1200 in all; but reckoning the lesser bristles, there will not be fewer than 3000; and there cannot be less than 100 suctorial tubes in each ambulacrum, making the number of exterior appendages in this creature 4000. We join in the conclusion of Baster:

"Quod si jam musculorum, ad aculeorum et proboscidum motum necessarium coniam animo concipiamus, Omni-potentem, que hæc animalia creavit, sapientiam attollit et venerabundì adoremus, necesse est."

The seas of warm and tropical countries are the most productive in Echinids; but the living species are few compared with the fossil, which are found principally in the chalk and oolite formations, in such abundance, and in so fine a state of preservation, that they are common and favorite objects in collections.

The direct uses of the Echinida to man are few and trivial. As its name indicates, the *Echinus esculentus* is eaten in some parts of the south of Europe; Pennant says, "by the poor in many parts of England, and by the better sort abroad." They are in season in spring, when the ova are most developed, and nearly fill the shell. They are recorded as among the favorite dishes of the Greeks and Romans. "They were dressed with vinegar, honied wine or mead, parsley, and mint; and esteemed to agree with the stomach. They are the first dish in the famous supper of Lentullus, when he was made *Flamen Martialis*, priest of Mars. By some of the concomitant dishes, they seemed designed as a whet for the second course, to the holy personages, priests, and vestals invited on the occasion." Epicharmus describes them as used likewise at the marriage feast of Hebe: "Thither came crabs and urchins, unable to swim in the sea, but travelling only on the ground." In the *Wasps* of Aristophanes, the old dicast, who is the hero of the piece, repeats a fable respecting an urchin, who, when his shell had been cracked by a woman, summoned witnesses to prove the assault. He is interrupted by the remark, that it would have been much wiser for the creature to buy a bandage. Ennius, in his *Phagetaea*, mentions "dules echini," and "calvaria pinguis," the latter evidently a species of Spatangus, which, we also know from Aristophanes, was considered a very dainty morsel. The Echinus is several times mentioned in Horace as good eating. The shells, cleaned and bleached, are pretty ornaments, with which finical idlers dress up their moss or summer houses, and naturalists their museums. Some fossil species are called fairy-stones, their spines elves' spurs; and with these names were once associated, as we learn from Sir Thomas Browne, suitable and terrible apprehensions, as well as medicinal virtues; "common opinion commendeth them for the stone, but are most practically used against films in horses' eyes." Once only has an Echinus been truly beneficial to our race. Some species of the genus *Cidaris*, we may observe, have very large prickles. The heathen children of the island of Rarotonga, in the South Seas, converted to Christianity by English missionaries, were in want of pencils with which they might be taught to write on slates; for these "they went into the sea, and procured a number of the Echinus, or sea-egg, which is armed with twenty or thirty spines. These they burnt slightly to render them soft, that they might not scratch; and with these flakes of stone for a slate, and the spine of the sea-egg for a pencil, they wrote exceedingly well; and hundreds of them took down the principal portions of every discourse they heard."

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1 The following epigram of Martial (xiii. 86) is very descriptive:

*Iste hicet cigitos testudine pungat acuta, Cortice deposito mollis echinus erit.*

2 *Opus. Subr. i. iii. pp. 119–114; also Fleming, *British Animals*, p. 476.*

3 *Annals of Nat. Hist.* i. 36.

4 See Kirby's *Bridgey Treatise*, p. 207. The largest spine of an Echinus on record is that noticed by Mr Gray, "nearly an inch and a half in circumference, and more than eight inches long."

5 *Ann. of Nat. Hist.*, i. p. 414.

6 *Opus. Subr. i. iii. p. 113. Professor Grant says, "There are more than 10,000 pieces in the shell of the *Echinus esculentus*, without counting the complicated dental apparatus of the mouth, or the respiratory and oval plates, or the very minute calcareous pieces disposed irregularly on the cortaceous membrane around the oral and the anal orifices."*

7 *Vulgar Errors*, p. 71.

8 *Williams's Missionary Enterprise*, p. 409.

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[From amongst the numerous systems of arrangement put forward]

Echinoderms by naturalists, we will select for analysis that of M. Desor, which includes both recent and fossil genera.

**Echinida Regularia.** Mouth below, rent above, both central; ambulacra in 5 pairs continuous from rent to mouth; ovaries 6.

Fam. 1. Cidaridae.—Interambulacral areas with 2 rows of plates.

Tribe 1. Augustinellidae.—Ambulacral areas narrow, composed of a great number of small plates bearing small granules; no buccal branches, ambulacra narrow.

Gen. Cidaris, Rhabdocidaris, Diplocidaris, Porocidaris, Goniocidaris, Leptocidaris.

Tribe 2. Latitellidae.—In place of simple granules on the ambulacral area, tubercles of the same structure, if not of the same dimension as those of the interambulacral areas.

Gen. Hemicidaris, Hemidiadema, Hemipedia, Hypodiadema, Pseudodiadema, Diplophora, Diademoides, Diadema, Savignya, Asteroptyx, Acrocladia, Acrocella, Phymosoma, Coptosoma, Catoptryx, Glyptocoma, Colophorus, Dellichthys, Prionotus, Echinocidaris, Glyptocoma, Phymosoma, Temnoschisma, Opechinus, Salmenia, Melanipilla, Microcyphus, Amblycyphus, Coelichthys, Colochirus, Echinocidaris, Cottalda, Magnoaria, Polyzygus, Paamachinus, Echinus, Stomachinus, Hyprechius, Styrechius, Tripneustes, Holopneustes, Botella, Phymocheirus, Spurechius, Toxopneustes, Heliocidaris, Loxechinus, Echinometra, Acrocladia, Podophora.

Tribe 3. Solasteridae.—Apical apparatus forming a sort of cushion of a peculiar form, and often curiously ornamented.

Gen. Arcosolenia, Peltaster, Gonophorus, Hyposalenia, and Salenia.

Fam. 2. Testellidae.—Interambulacral area with 5 or 6 rows of plates.

Gen. Archoncidaris, Eocidaris, Perischodus, Paleochina, Melonites.

**Echinida Irregularia.** Mouth below, rent sometimes below, sometimes at one side; ambulacra not continuous.

Fam. 1. Galeritidae.—Test circular or pentagonal, peristome central, decagonal, or pentagonal; periproct independent of the genital apparatus, superior or inferior; pores simple.

Tribe 1. Galeritidae veræ.—Ambulacral areas simple, with a masticatory apparatus.

Gen. Pygaster, Pileus, Galeopygus, Holotypus, Discolobus, Echinocoma, Galerites, Globator, Anorthopygus, Nuceloptygus, Pyrma, Hyboclypus, Desorella, Pachylypus, Asterostoma.

Tribe 2. Echinocidariidae.—Ambulacral areas simple; no masticatory apparatus.

Gen. Echinomimus.

Fam. 2. Dynasteridae.—Test ovoid or cordiform, elongated, rarely circular, peristome more or less excrescent; periproct at the posterior face; pores simple, ambulacra disconnected.

Gen. Dynaster, Collyrites, Metaporphus, Grasia.

Fam. 3. Cypraeasteridae.—Ambulacra petaloid; peristome central; masticatory apparatus composed of five triangular jaws.

Tribe 1. Cypraeasteridae.—Interambulacral areas very narrow; petals lanceolate, generally open; ambulacral furrows of lower face anastomosing; peristome circular, surrounded by a buccal rosette and five tubes.

Gen. Echinocyamus, Fibularia, Ruma, Moulinia, Lemis, Scutellina, Siamondia, Lagunaria, Rumphia, Arachnoides.

Tribe 2. Scutellidae.—Form circular; ambulacral furrows of inferior face always anastomosing; external branches intruding on interambulacral areas.

Gen. Echinarchinus, Mortonia, Scutella, Dendraster, Monophora, Lobophora, Amphipogon, Mellita, Encope, Rotula, Echinodiscus.

Tribe 3. Cypraeasteridae veræ.—Petals much developed, much larger than the interambulacral areas; peristome sunk; furrows of inferior face straight, not anastomosing; each jaw pivoted on two auricles instead of being simply supported on them.

Gen. Clypeaster.

Fam. 4. Cassidulidae.—Ambulacra petaloid; no jaws; peristome angular, central, or subcentral.

Tribe 1. Cassidulidae.—No floecule.

Gen. Caratomes, Pygaster, Amblypygus, Halmen.

Tribe 2. Echinanthidae.—Floecule more or less developed round the peristome.

Gen. Nucelites, Echinobrisseus, Clypeopygus, Clypeus, Botriopygus, Catopygus, Oolopygus, Rhynchoopygus, Cassidulus, Echinanthus, Stigmatoopygus, Pygorhynchus, Barholia, Echinolampus, Pygurus, Fauglas, Conoecypus.

Tribe 3. Clavasteridae.—Forms strange, with a peculiar structure of ambulacra, especially the odd ambulacrum.

Gen. Archonia, Clavaster.

Fam. 5. Spathangidae.—Ambulacra petaloid; peristome excentric; no jaws; periproct posterior or infra-marginal; four genital plates; two broad smooth avenues at the interior face, corresponding with the posterior ambulacral areas, and surrounding a tuberculated heart-shaped space, corresponding with the odd interambulacral area.

Tribe 1. Acanthidae.—The petals on a level with the test are not closed at their extremities; poriferous zones approximated and scattered at the borders.

Gen. Amachytes, Stemona, Offaster, Holaster, Cardiaster, Infusaster, Hemipneustes.

Tribe 2. Spathangidae veræ.—Even ambulacra distinctly petaloid; apical apparatus compact, so that the genital plates are always approximate.

Gen. Toxaster, Endaster, Isaster, Micraster, Hermaster, Brisus, Peraster, Schizaster, Agassizia, Moers, Linhul, Percomus, Toxorbrissus, Precaster, Brisus, Flagelatus, Qualiciaria, Echinocardium, Breynia, Macropneustes, Equatagus, Hemipneustes, Spathagus, Meoma, Paorina, Kleinia, Leckla.

Order 3.—Stellerida (Asteroidea).

The "seas have stars," sings Du Bartas; and if challenged, he would probably have appealed to the members of this family in proof that his fancy was in this instance not more licentious than his verses. But it is only some species which have felt the skyey influence over their forms; for even certain of the Asterias are merely pentagonal, and some square, while the total forms of other genera rather imitate a wheel in their faces, with spokes radiating from a central navel: and others again have sought no impress from any object in the heavens or in earth; for though they have been called "lily-shaped animals," yet is the semblance but postulatory, and he must have a more assimilating fancy than our own who perceives it in these objects. Amid this diversity of forms, we may nevertheless remark, that a line drawn so as to connect the species of the rays together would give a circular outline to the body, which is very rarely protuberant, and never globular. It consists of two parts, the disc and the rays; the latter either continuous and homologous, or dissimilar and articulated to the other by the medium of peculiar scales. There is always a distinct dorsal and ventral surface; the former in general vividly coloured, and covered with spongyous tubercles or scales, whose office is defensive; the latter colourless, and furnished with the organs of locomotion and of touch. The colour resides in the mucous coat that occupies the place of the epidermis of higher animals, but the scales and tubercles are essentially parts of the

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1. Synopsis des Echinides Fossiles, par E. Desor, Paris, 1858. The reader may also consult various memoirs by Johannes Müller, printed in the Trans. of the Berlin Acad., and Dr T. Wright's Monograph of the British Fossil Echinoderms, Palaeontographical Soc. 1855-58.

2. Pliny begins his work De Stella Maris thus:—"Non cerio tantum, sed et mari sum stelle sunt, opera quidem unius Dei artificis, sed diversis formis fabrica e nature." In his Enquiries into Vulgar and Common Errors, Sir Thomas Browne has a chapter entitled "That all Animals of the Land are in their kind in the Sea," which, he rightly says, "although received as a principle, is a tenet very questionable, and will admit of restraint." After some good remarks, the chapter concludes with the following passage, and such passages abounding in the works of this learned physician render them delectable reading. "Lastly, by this assertion we restrain the hand of God, and abridge the variety of the creation; making the creatures of one element but an acting over those of another, and conjuring, as it were, the species of things which stood at distance in the intellect of God; and though united in the chaos, had several seeds of their creation. For although in that indistinguishable mass all things seemed one, yet separated by the voice of God, according to their species, they came out in incommunicated varieties, and irreducible seminialties, as well as divided places; and so, although we say the world was made in six days, yet was there, as it were, a world in every one—that is, a distinct creation of distinguishable creatures; a distinction in time of creatures divided in nature, and a several approbation and survey in every one." Book iii. chap. 24. Echinoder-thick cretaceous skin which gives figure and consistency to the whole. In this skin there is deposited a considerable proportion of carbonate of lime, with some phosphate of the same earth, sometimes in the form of scales, either imbricated or scattered; more usually in grains or short pieces, so joined as to make a sort of knotted thread, that, by its divarications and anastomoses, is woven into a netted frame-work, the interstices of which are filled up by the mucous tissue. On the calcareous frame-work the spines and tubercles are placed, and these vary in size and structure according to their position. When dorsal, they are mostly short and obtuse, unordered and immovable, excepting in so far as their degree of erection and relative position may be effected by the more or less turgid condition of the body; but on the sides of the rays, while their size is greater, they are also dressed in regular lines, and appear to be capable of being moved backwards or forwards by peculiar muscles. In the Asteroidea, the under surface of the rays is deeply furrowed from their origin to their extremity; and the furrow, analogous to the ambulacra of the Echinidae, is occupied with two or four series of tentacular feet, which are also guarded by moveable spines, different in their structure, however, either from those of the back or sides, and forming a protective hedge on each side. There is nothing similar in the Ophiuridae or Crinoidea, whose rays are not grooved, nor possess tentacular feet, but consist of a succession of similar pieces soldered to each other, so that they resemble the vertebral column of some slender animal, or, more exactly, from the squamous nature of the pieces, the tail of a lizard; and, like that tail, they are tapered and flexible to a certain extent, and equally brittle. It is interesting to remark, that this ray, apparently very dissimilar from that of the Asteroidea, really finds in that genus its type and original; for the roof, if we may so speak, of the ambulacral groove is made up of a series of pieces catenated exactly like those of the Ophiuridae, with compressed processes arching up from each side after the manner of ribs, between whose intervals the tentacular feet are extended.

The mouth is situated in the centre of the ventral surface. It is a circular orifice, with a membranous lip, capable of great dilatation, but bounded by spinigerous and tuberculated angular projections, formed by the convergence of the bases of the rays, that may be useful in capturing and bruising the prey. A short oesophagus leads to the stomach, a large membranous sac occupying the centre or nave of the body; and though connected to the parietes by several ligaments, yet sufficiently loose and dilatable to permit of its frequent eversion and extrusion in the shape of bladder-like lobes. It has no intestine, excepting in the Crinoidea family, where there is a distinct vent opening on the interior surface, near the mouth. But the nutritive parts of the food pass from the stomach either into sacculated reservoirs, as in Ophiura, or through narrow vascular passages into large complicated cecal appendages, which lie along the floor of the rays, two in each ray, consisting of a regular series of pectinations or overlying lobules, and having no unapt resemblance to some beautiful compound leaf or fern. Such organs we find in the Asteroidea; and as it circulates through them, the chyle is largely subjected to the influence of the oxygenating medium, and prepared for its assimilation. Such at least is the opinion of Tiedemann; but it may be necessary to mention, that Cuvier, Blainville, and Meckel regard these ceca as secreting organs, analogous to the biliary organs of many invertebrate animals, with which, says Dr Sharpey, it must be allowed they agree in several respects. In the living animal they are bathed, or rather float, in sea-water, which is presumed to be introduced within the body by means of numerous small tubular filaments that rise up on the back between the tubercles, penetrating the soft parts of the skin; and it is ascertained that the water, after a time, may be expelled through the same conduits, for there is no doubt of the animal's ability both to fill and empty its body. The animal, observes Dr Sharpey, slowly distends itself with the water, "and again, but at no stated interval, gives out a portion of it: this is obvious from the fact, that the same animal may be seen distended at one time and flaccid at another. Naturalists are generally of opinion that the water enters and issues by the respiratory tubes (or dorsal filaments), and indeed no other orifices have been discovered; we must, however, freely own that we have never been able actually to observe its passage through these tubes." In the Ophiuridae, in whom these tubes are not to be found, there must certainly be other entrances for the fluid; and these are probably certain orifices situated on the ventral surface, near the base of the rays. The water, however introduced, is there for the purpose of respiration, the principal seat of which seems to be the peritoneal membrane. "Spread over the viscera and the parietes of their containing cavity, and lining the respiratory tubes, it presents a great extent of surface, continually in contact with the surrounding medium; and we have found that a beautiful provision exists for maintaining currents of water along the membrane, and thus effecting that constant renovation of the fluid in contact with its surface which is required in the respiratory process. These currents are produced by means of cilia." ... "Ciliary currents take place also on the external surface of the body, which probably partakes in the process of respiration; we have moreover observed them within the tubular feet, and on the internal surface of the stomach and ceca: in this last situation they are probably subservient to digestion."

The mode of progression of the Stelleridae is probably limited to a sort of creeping; but their walk is not so slow as the language of most authors would induce us to believe; nor have we been able to ascertain, from many observations, that any one or two rays have a preference for the van, as has been insinuated, but whatever ray happens to point toward the object or place in view, is made the leader for the time being. The organs of locomotion are very different in the different families. The rays of the Asteroidea, as already mentioned, are broadly furrowed underneath, the furrows planted with soft tentacula, which are flexible in every direction, being moved by circular and longitudinal muscular fibres, which enter copiously into their structure. In form, these tentacula may be compared to a retort or Florence-flask with a long neck; the swollen vesicular bulb is placed within the cavity of the rays on each side of their mesial vertebated column, while the neck issues from between the interstices of its side-pieces, and protrudes outwardly. They are hollow, being filled to a certain degree with water, introduced by a set of

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1 Gray in Annals of Philosophy, n.s. xii. p. 392. 2 Reaumur in Linck. de Syst. Mar. App. p. 93. Ehrenberg has discovered that these filaments are inwardly clothed with vibratile cells, and he believes there is within them a circulation, not of water, but of a fluid analogous to blood; for he says we see in it globules altogether like the blood-globules of other animals. Ann. des Sc. Nat. n.s. iv. p. 304. 3 Sharpey in Cyclop. of Anat. and Phys. ii. p. 40. 4 Baster (Oph. Sub. i. p. 119) and Bose say that the Asteroidea can also swim. "In this act they suspend themselves obliquely in the water, and with their rays produce slight undulations, which suffice to direct their course. When they wish to descend, they cease these motions, and immediately sink to the bottom." Hist. Nat. des Vert. ii. p. 125. Blainville has seen certain species of Asteroidea swim swiftly. Man. d'Actinologie, p. 241. When the star-fish wishes to elongate any particular tentaculum, it contracts the vesicular bulb, and the water in it is consequently forced up the neck, distending and stretching it, and putting it in a fit condition to be applied against the ground or any object within reach. To this the extremity is affixed by the action of the muscular fibres, some contracting the centre of the point into a dimple, and others firmly appressing the edge, so as to give it the form as well as the virtues of a sucker. Now, by shortening the tubes which have been so fixed, the body is drawn towards their insertion; and by a curious succession of these actions, the creature goes whither it has willed. It is impossible to follow the exact succession of the retraction and elongation of the suckers, nor, indeed, do they seem to be called into action after any regulated plan. Some are employed as stilts merely, on which the body is raised up buoyant in the circumfluent medium, while others are pulled in and stretched out to act as legs or feet; and others again seem to be used, more especially for the time, as seekers and feelers, that no prey may pass unawares, while the main object in view is apparently only a change of place. But the Ophiurae progress by a very different apparatus. "The diverging rays are firm and hard, have few spines, and no channel with suckers; they are used by the animal as legs, and as they are regularly placed, it can move in any direction that suits it. To go towards any particular spot, it uses the two rays that are nearest to it, and another that is most distant from it; the two first curve at their extremity, so as to form two hooks, which, being applied to the sand, drag the body forwards, while the posterior is curved vertically, and performs the part of a repelling lever." This action of the rays is assisted by some subsidiary organs, which have been hitherto unnoticed. On examining the rays of a living Ophiura, we have noticed that every one of their articulations is furnished with a pair of strong sharp moveable claws, similar to those of many insects and crustaceans; and from their position under the lateral spines on the ventral aspect, not more conveniently placed for taking hold of a plain surface than their form has an obvious adaptation to that act. They are unquestionably organs belonging to locomotion, which seems to us to be further aided by some filamentous tentacula that issue from pores in the ventral disc, whose function, though mainly respiratory, may be in a secondary degree locomotive, by serving as stayers to support the body, and elevate it above the unevenness and friction of the surface traversed.

The nature and number of the senses bestowed upon the Stellerida is a subject of doubtful inquiry; for the organs of these senses are either so far removed from ours that analogy offers no clue to their function, or the resemblance is so forced and superficial that it may possibly lead us to very erroneous conclusions. There is no reason to doubt that the species are richly endowed with the sense of touch; but it is doubtful whether any part or organ possesses that modification of the senses on whose discrimination the luxury of taste depends. It is equally doubtful to us whether any have visual organs, for that blindness is the lot of most of them is granted. Ehrenberg, however, when examining living specimens of the *Asterias violacea*, discovered a point of a bright red colour, precisely defined, situated beneath and towards the apices of each of the five rays. This point he believes to be ocular; and to give scope and direction to the organ, the star-fish curls back the tip of the ray when in the act of progression. Ehrenberg succeeded in tracing some nervous filaments to the apex of the rays, where he also found a small ganglion placed near the eye. In front of this ganglion, towards the mouth, there are some jointed nervous fibres; but similar articulations are not visible in the nerves situated near the mouth itself; whence this illustrious naturalist concludes, that the noblest part of the nervous system is found towards the apices of the rays. But what office are we to assign to those anomalous organs, which, in the Echinida, Monro has compared to insect antennae? They exist in the Stellerida, principally on the sides of the rays hid among the spines. "Each consists of a soft stem, bearing at 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 Stellerida are oviparous, the ovary forming a grape-like cluster placed near the origin and at the sides of the cæca, for there are two ovaries to each ray. The eggs lie numerously imbedded in a colourless jelly, covered with a thin pellicle, and are at first equally colourless; but during their progress to complete development, they pass through a great variety of colours, and when fully formed, assume invariably the distinguishing shade observed in the adult animal. They escape from the body by certain apertures, observable at the side of the mouth in the angle of separation of the rays; and the greater number of the species are said to deposit their spawn in spring. When excluded from the egg, they are, according to Saars, very unlike the parent, for they are then binary, and do not become radiated until after some weeks.

The Stellerida are richly endowed with the wonderful property of reproducing parts which they may have lost from accident. In summer, it is asserted by Bosc, the parts pullulate and attain their original size in the course of a few days, while in winter some months are required for such production; but this is one of these loose assertions in which the works of Bosc abound. The time really required is much longer, though not exactly ascertained, and seasons probably influence it in no great degree. One ray lopt off, or two or three, all grow again; nay, a single arm, provided any portion of the disc remain attached, will live and become cinquefoil, as it was previously to its miserable mutilation. There was a time when these phenomena gave rise to expressions of the greatest wonder, and to speculations more curious than edifying, touching the possible divisibility of the soul, and other metaphysical subtleties. We may safely infer from them, that the susceptibility to pain in these animals must be very considerably, and almost infinitely, less than in animals of a more perfect kind, since in these the pain consequent on such injuries... Echinoderms, and the sympathetic fever which follows as its necessary result, would be sufficient to kill them, independently of any other cause.

In relation to habitat, the Stellerida may be enumerated among the denizens of the shores of every sea, living generally at a depth of several fathoms, where they congregate in incalculable herds. There are beds of some species on our own coasts that spread over an extent of some hundreds of yards, lying, in some spots, one upon another, to the thickness of a foot or more. The species are more various, if not more productive, in tropical than in temperate or cold seas. They prey upon small testaceous molluscs, which they catch with their suctorial feet, and retain opposite the mouth by means of the spinous projections surrounding it. We have found in their stomachs various univalved species, but the conchifera are supposed to be more especial favourites. M. Eudes Deslongchamps has observed five or six individuals of *Asterias rubens* clustered together in the form of a ball, the nucleus of which was a Macra. The star-fish had retroverted their vesicular stomachs, and were found endeavouring to suck out the fish from between the valves of the shell; but it is impossible to believe, with this naturalist, that the Asterias had separated, or were capable of separating them, so as to inject within a fluid capable of benumbing the mollusc and placing it beyond resistance, the more especially as this fluid has no other than imaginary existence. There can be no doubt that the valves had partially opened, from the feebleness or death of the mollusc, before it was set upon by the star-fish. We have seen similar clusters around a Turbo or whelk. Deslongchamps's opinion is indeed only worth notice as coinciding with that of the fishermen, who, regardless of the certain inefficiency of the agent, are fond of telling of the exterminating war waged by the Asterias against the oysters; a tale which has its invention at a distant date, being found in Aristotle, paraphrased by Ælian, and versified by Oppian, and hence copied without question by every subsequent popular compiler.

In their turn, the Stellerida are greedily preyed upon by fish of almost every sort; for they who assert that the acridity of their flesh, or the spines and prickles of their skin, render them distasteful or formidable, know nothing of the voracity and power of their foes. We have very often found the stomach of cods and haddock crammed with the remains of star-fish, more especially of the prickly Ophiuroids, and that at a season when the fish were in high perfection. Dr Knox has attempted to prove that the ova of the Echinodermata are the proper food of the salmon, which is only fit for the table of the epicure when he has been feeding on them: "from the richness of the food on which the true salmon solely subsists, arises, at least to a certain extent, the excellent qualities of the fish as an article of food." Vast numbers are more certainly destroyed by the fisherman, who finds they materially injure the produce of his art, by clinging to and clustering round his baits, and who therefore wreaks his vengeance on them by throwing them in heaps on the dunghill. In some places the common species have even been used as manure; but otherwise man has not found them adapted to his use, for the medicinal virtues which the early physicians and astrologers ascribed to them, have disappeared in their modern generations.

To remedy that looseness of description which of necessity belongs to such general views as we have been giving, we proceed to notice the systematic arrangements of the order, whose only common characters seem to be a depressed multitudinous carapace body, with rays or lobes radiating from the margin of the disc, and an inferior central mouth.

Cuvier adopted the genera of Lamarck. The genus Encrinus, which Lamarck had referred to the Zoophytes, Cuvier properly placed near Comatula, adopting the views of Miller implicitly in regard to its structure and further subdivisions.

Miller names the family of which the Encrinus may be considered the type, Crinoidea, or lily-shaped animals, a family rendered interesting not only by their curious forms and extraordinary structure, but also by their being among the earliest inhabitants of this planet. Hence they are so far aliens of this world, that whilst immense tracks of rocks are literally formed of the embossed remains of different species in a mineralized condition, only five or six species have yet been discovered in a recent state. An idea of their structure may be obtained if we imagine an Asterias placed with its mouth upwards on a columnar jointed stem, one end of which is connected to the dorsal surface of the animal, and the other most probably fixed at the bottom of the sea. The rays or arms extending from the circumference of the body are much branched, and at last pinnated; other jointed processes, named auxiliary arms, surround the stem in whorls placed at short intervals. The column is perforated in its centre with a narrow canal, down which a prolongation of the stomach extends, and lateral canals proceed from the central one through the verticillate auxiliary arms. The Comatula has rays spreading from the circumference of the body, branched and pinnated like those of the Pentacrinita. It is not fixed on a column, but the dorsal surface of the body is elevated in the middle, and bears a number of smaller rays or arms; and this dorsal eminence, with its rays, has been sometimes compared to a ramification of the column of the Pentacrinita with its auxiliary arms. Besides the mouth, there is an anus opening on the ventral surface, situated on an eminence near the margin. The exactness of the comparison here drawn between the Comatula and Pentacrinita, first detected by the acuteness of Miller and Gray, has been singularly illustrated by the discovery of V. Thompson, that Pentacrinita is only Comatula in its first stage of existence; the head, in the progress of development, separating from the stem, to become, instead of a fixed pedicellated floriform zoophyte, a nomad star-fish in the bosom of the ocean. In their fixed condition, the Crinoidea appear to have had a considerable range for the seizure of their prey, without possessing absolute locomotion.

Still moving, yet immersed from their stem:

for the peculiar mode of the articulation of their vertebrae probably afforded them a great degree of mobility, with considerable security against dislocation. They grow erect, the stem being in general sufficiently stiff and strong to support the heavier head; but when it is not so, as in the Umbellularia, we find that, just under what has been called the pelvis, "a hollow bladder-like membrane" embraces the upper part of the stalk for about two or three inches, and, performing the office of a buoy or swimming-bladder, keeps the head in an upright position.

**ASTERIADAE.**

Distinguished by the possession of a single orifice of the intestinal canal, surrounded by suckers, but void of teeth; while deep grooves, containing several series of pedicles, extend from the mouth to the extremity of the rays. On the dorsal surface, we remark between the two posterior rays a calcareous wart, convex externally, and grooved like a madreporite, which has therefore been denominated the madreporiform tubercle. It covers a singular organ, named the stone-canal by Tiedemann, who believed its office to be the secretion of the earthy matter required for the growth of the calcareous skeleton. The accuracy of his description of its structure has however been called in question; and the opinions relative to its function are various and contradictory. Blainville considers it to be in some way connected with generation; and from its variations he asserts we may draw our most permanent characteristics of the species. It is almost certain, he also tells us, that there is a distinction of sexes among them, and consequently a sexual union; and indeed Otho Fabricius says that in the month of May in Greenland they are to be found in pairs united face to face.

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1 Good's Book of Nature, i. 429. 2 Edin. New Phil. Journ. ii. p. 394. 3 Blumenbach's Man. of Nat. Hist. trans. p. 267. 4 "On the Nat. Hist. of the Salmon," &c. p. 8, a pamphlet from the Trans. of the Roy. Soc. of Edin., vol. xii. The same food is said to communicate poisonous qualities to the mussel. 5 Kirby is led by his speculations to believe that the extinct forms still exist in the deepest abysses of the world of waters. 6 Sharpay in Cyclop. sup. cit. p. 32. 7 Parkinson in ibid. cit. p. 96. 8 Ellis's Corallines, p. 97. 9 Man. d'Actinologie, p. 237. 10 Ibid. p. 236. The Ophiuridae are distinguished by the central part of their body forming a distinct and flattened disc, to which are annexed more or less elongated and even ramified rays, with no grooves on their surfaces. They are oviparous animals, and have no true suckers by which to walk; their progression being effected (and with great facility) by means of five long flexible jointed processes, placed at regular distances round the body, and furnished with spines on the sides and membranous tentacles. These processes are very different from the arms of the true star-fishes, which are lobes of the animal's body; whereas the arms of the Ophiuridae are superadded to the body, and there is no excavation in them for any prolongation of the digestive organs. The stomach is a sac with one aperture, its walls externally covered with vibratile cilia. The ovaries are not branched; they are placed near the arms, and open by orifices near the mouth, between the origin of the arms. Their investing membrane is also ciliated, but on the rest of the body and arms no cilia exist; hence we may conclude there is no separate respiratory system."—Edward Forbes.

[Without going further into the history of the various arrangements proposed by naturalists, we will content ourselves with tabulating that given by Müller and Troeschel in their System der Asteroidea (Brunswick, 1842), who thus marshalled the genera:—

**ASTEROIDEAE.**

Locomotion by cirri issuing from the under side of the radial arms which are continuous with the body.

Fam. 1. Arms with four rows of cirri. A vent. Gen. Asterocanthion. (Asterias, Uraster.)

Fam. 2. Arms with two rows of cirri. A vent. Gen. Echinaster (Asterias, Crinella), Solaster, Chetaster, Ophiaster, Dactylosaster, Tamarina, Cistina, Seytaster, Culcita, Asterocerus (Palmipes), Pteraster, Oreaster, Astrogonium, Goniocidus, Stellaster, Asteropus, Archaster.

Fam. 3. Arms with two rows of cirri. No vent. Gen. Astropecten. Aenodiscus, Luidia.]

**Ophiurideae.**

Locomotion by spines; radial arms as appendages to a discoid body.

§ 1. OPHIURIDAE. Arms simple.

Fam. 1. Four genital clefts in each interbrachial space. Gen. Ophioderma (Ophiura), Ophiochemis.

Fam. 2. Two genital clefts in each interbrachial space. Group 1. Genera with papillae round the mouth. A. Arms and disc with hard parts. Gen. Ophiolepis, Ophiochoma, Ophiarachna, Ophiacantha, Ophiomantis. B. Arms and disc naked. Gen. Ophionyx, Ophioscolex.

Group 2. Genera without papillae at the mouth. Gen. Ophiotrix, Ophioxyx.

§ 2. ECHYTALE. Arms branched. Gen. Asteronyx, Trichaster, Astrophyton.]

There now only remains for consideration the order

**CRINOIDEAE.**

The Crinoidea, notwithstanding their star-like form and their great external resemblance to the Ophiuridae, constitute however a distinct order, characterized by the presence of two separate orifices to the intestinal canal, although very near to each other. These orifices are by no means easily distinguished among the rays which surround them, especially in the fossil species. The greatest part of the species are pelagic, i.e., carried on a float-stalk adhering to the centre of the region, which, in the star-fish, we consider as the middle of the dorsal surface.

Genus Comatula, Lam.—Disc pentagonal, arched at its upper surface, which bears several series of simple and articulated rays; rays of the disc bifurcate, beginning however with two simple pieces. The edges of the rays are pinnate; mouth central, sunk anus between the mouth and the border of the disc, obliquely proeminant. Animal free when mature, but fixed and pedicellate when young.

Mr. J. V. Thompson discovered that "the body of the Comatula, when the animal is kept in a small quantity of sea-water, is soon detached, entire and perfect, from the cavity in which it is lodged, and in this state it might be mistaken for an animal of a very different tribe." He suspects that the genus Massmaria of Müller may have no better foundation. The same naturalist has made the Acalepha still more singular discovery that the Pentacriniite of the Irish seas, which he first described under the name of Pentacrinius Europaeus, and which has since been made the type of the genus Phytocrinus by De Blainville and Agassiz, is a Comatula in its earlier states of development. When not more than one-eighth of an inch in height, this Pentacrinius resembles a little club, fixed by an expanded basis, and giving exit at its apex to a few pellucid tentacula; no other part of the solid fabric is observable, but an indistinct appearance marks the place where the animal would have made a little more progress, together with the elongation of the pedicle or stem, its joints begin to make their appearance; the body acquires a larger size and brownish tint, from a groser food; the tentacula of the mouth protrude in a greater degree, and move slowly in various directions. In others still more advanced, the joints of the stem become quite obvious, from their opacity and white colour, and the base of the future arms, as well as the auxiliary side-arms, are rendered palpable. The arms from this period lengthen space from their bifurcation, and have superadded to them a double range of transparent jointed tentacula; so that the animal begins to put on a more perfect appearance, and now for some time merely acquires a somewhat greater size, and an extension of its arms, which, although they solidify from their origin upwards, remain pellucid and thick at their apices, where elongation, evolution, and the secretion of calcareous matter is gradually going on." Subsequently the arms again bifurcate at or near to their extremities, a second time often at the same time; and having attained full development, entitling it to the name of a Pentacriniite, the head appears to be cast off, that it may become a nomade Comatula. How just, then, the conclusion of Mr. Thompson from these interesting discoveries: "From these observations connected with the growth of this animal, and by which it appears to present itself at various stages of its progress under considerable diversity of form, naturalists may learn to avoid the unnecessary multiplication of the genera and species of the Crinoidea, by giving undue weight and consideration to characters originating in the progressive evolution of individual species, and which are consequently of a transitory and delusive nature."

Genus Comaster, Ag.—This genus has the same organization as the preceding, but the arms are ramified instead of being simply furcate.

Genus Pentacrinius, Miller.—Pedicle more or less pentagonal, bearing at intervals simple vesiculatae rays; rays of the disc fixed to the pedicle, each by a cuneiform plate composed of two simple pieces, after which the rays bifurcate, and at a little farther distance divide into two, which then branch out into numerous appendices, pinnate at their edges. The space between the base of the rays, occupied by the visceral cavity, is formed by numerous small lamellae. The only living species (P. copus Medusa) is a native of the Caribbean seas.

III.—ACALEPHIDAE.—SEA-JELLIES.

The Acalephidae have been named by Blainville the Arachnodermata, to mark in a stronger manner how remarkably they contrast with the Echinodermata in the structure of the skin, which is a soft serous pellucid cuticle, containing sometimes miliary granules, but always smooth and even, and as thin as the gossamer's web. They are radiated animals of a gelatinous consistency, with an unarmed mouth in the centre of the ventral surface, the entrance into a stomachal cavity without proper parietes, but furnished with vasculiform canals ramified through the body; their respiratory apparatus is ciliary, and their mode of generation oviparous; they are all nomade and marine, and move through the water by alternate contractions and dilatations of their periphery, or by the aid of vibratile cilia. The constituents of the class are divisible into two orders—viz., 1. The Medusidae, with a body almost always circular, convex dorsally and concave below, supported in a few genera by an internal cartilaginous plate; the rim as well as the oral aperture, mostly fringed with tentacular ciliated appendages; 2. The Acalephidae properly speaking, whose body is irregular and multiform, bilateral, and sometimes orbicular, with brachial or filamentous appendages, and ciliary fringes.

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1 See J. V. Thompson's Memoir on the Pentacrinius Europaeus, Cork, 1827, 4to; the Edin. New Phil. Journal for 1836; and Edward Forbes's History of British Star-Fishes. Among animate creations, there is none that excels the Medusidae in beauty and ornament, or in the variety and eccentricity of their forms; there's not a gem wrought by man's art to be compared to them; soft, brilliant, tender, through the wave they glow, and make the moonbeam brighter where they flow.

When floating in the ocean, most of them appear like crystal bowls of the purest transparency, veined and patterned with the most brilliant colours, and their rims ornamented with fringes, fur-below, and arbustes of such delicacy and intricacy of workmanship, that even the most experienced in Nature's works marvel how it is that such textures, too frail to bear the lightest handling, are kept entire amid the restless element of their nativity. We have often watched with intense interest some of the least complicated, and, it may be, some of the least beautiful, as they floated by us on the surface of a summer sea. On a hasty examination, they may seem to be supported there by their own inherent buoyancy, and to be carried onwards with the tide or current, which they have apparently no power to resist; but watched a while, they are seen alternately to contract and expand the whole periphery of the body at regularly-timed intervals, in a manner which Dr Roget has aptly illustrated by comparing it to the opening and shutting of a parasol, and with a quickness and force which we have felt to be considerable. By these motions the Medusidae can swim against a gentle current, though they more commonly yield themselves up to its persuasive violence; and when alarmed, they can also sink deep into the bosom of the sea with considerable velocity, so as frequently to elude an attempt to secure them. They can stop and maintain themselves at any depth, and rise again with equal ease to enjoy a nearer intercourse with light and air. Lamarck's speculations rendering it necessary to deny to them either nerves or muscles, he has persuaded himself that these motions of the body are entirely mechanical, produced by the influx and efflux of imponderable fluids, such as electricity, permeating and flowing through its gelatinous texture; but we are very sure that he will summarily reject this theory who has once observed the phenomena, which are certainly in some degree under the control of the animal, and regulated by its will and sensations. It seems indeed to be now proved, more especially by the anatomies of Ehrenberg, that they are the effects of the contraction of muscular fibres, radiating from near the centre of the body to the circumference, running alongside the vein-like nutritious canals, and by others in the rim, which have a circular direction. We know also that the Medusidae do possess a nervous system, formed after the same plan, and rather more complete than it is in other radiated beings.

The figure of the Medusidae is regular and almost always circular (for the Velella alone are oval), sometimes discoid or spheroidal, but generally hemispherical, so as to allow of a comparison between them and the mushrooms, which they are presumed to represent in the animal kingdom; and the same fancy may see in them the living models on which our umbrellas have been made. The margin is usually fringed with tentacular filaments; and in many species we also observe, placed at wide intervals, a circle of coloured warts, which, from their organization, are evidently organs of importance in the animal's economy. Ehrenberg believes them to be branchial, for connected with each of them he has discovered a partial circulation of a fluid analogous to blood; and, what is still more singular, he has detected in their near vicinity an organ retractile; Acalepha within a sheath, and containing a mineral crystal, to which he assigns the office of an eye, because it is similar in structure to the eye of several infusory animalcules, and is more amply provided with nerves than any organ other than one of sense ought to be.

The under surface of the umbrella is sometimes entirely naked, sometimes furnished with numerous scattered tentacular suckers, as in Porpita and Velella, or with greatly diversified brachial appendages, which depend usually from the lips of the mouth. These are either free from each other and separate to the base, or they coalesce so as to form a kind of stalk previous to their ramification into lobes or filaments, each division having at its extremity pores for the absorption of the thin nutriment on which such species must necessarily subsist. The Medusa, with this structure, resemble a bulbous root with its radical fibres, and were therefore called Rhizostomes by Cuvier. The greater number of the Medusidae, however, have a distinct mouth, placed always centrally, either scissile or at the end of a species of proboscis more or less prolonged. It has no hard parts, nor teeth, nor jaws, and leads by a very short oesophagus into the stomach, consisting frequently of four separate cavities excavated in the gelatinous parenchyma, without any peculiar lining. From the stomach proceed numerous vessels, which all bend to the circumference. Some of these vessels are simple and undivided, others ramify dichotomously like veins, and form anastomoses among their ultimate divisions. Injections from the stomach pass more readily into the simple than into the ramose vessels; but both kinds serve for the conveyance of the digested food, whose unassimilated remains pass from the body through their extremities, which open by apertures on the rim. The portion intended for nutrition and growth probably transudes in part into the parenchyma, while it flows along the vessels; and a part seems to enter a peculiar vessel which runs round the periphery that it may pass into the partial circulations at the marginal tubercles, and be submitted to the action of the air. It must, however, be admitted that these tubercles exist in comparatively few species; and there can be little doubt that the principal airing of the nutritive fluids is effected by the action of the circumfluent water on the exterior surface, as well as in the internal cavities and vessels. To effect this great purpose more completely, we find that the oral and marginal filaments are clothed with vibratile cilia, which drive currents of water over them in determinate directions; and these cilia are said likewise to line some of the interior cavities. It is from their action that portions cut off from the appendages continue to move like independent and perfect beings—a circumstance apparently so demonstrative of their completeness as to have given origin to several spurious species.

The Rhizostomes, as we have already mentioned, feed only on fluid matters, and such also is the condition of those genera which Peron and Le Sueur named agastric, from a belief that they had neither mouth nor alimentary sacs; for although this latter statement has been shown to be erroneous, yet the absorption of the aliment appears to be through ports. But the bulk of the Medusidae love a grosser fare, and there is some slight evidence in favour of their having a discrimination in the matter; for Gaede remarks that he has never found fishes in the stomach of Medusa capillata, but often worms; while in that of Medusa aurita there are frequently fishes, rarely worms. The latter species, according to our observation, feeds more frequently

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1 See Kirby's Bridges, Treat. i. p. 199. 2 Anim. Vert. ii. pp. 444, 446, and 452-5. 3 Ann. des Sc. Nat. n. s. iv. p. 290, &c. 4 Régne Animal, iii. p. 278. Figures illustrative of the structure are given in the Bridges' Treatise of Dr Roget, ii. pp. 888-9. 5 We may here warn the student that he should guard against the too great extension of these general remarks; for the truth is, few species have been examined anatomically, and even the most general detail will be found to have many individual exceptions. ZOOPHYTES.

Alephus, on pelagic Gammarus; and minute crustacea and entomos- traca constitute the principal food of most of them. Digestion is extremely rapid. We remember once observing in the stomachs of Medusa aurita several specimens of a Gam- marus unknown to us, and which we were anxious to examine: they were living when first seen, and when we left the Medusa in a basin of sea-water for half an hour, we little dreamed of the disappointment awaiting our return, for not a trace of the crustacea was then visible.

All the species are propagated by ova generated in appropriate organs situated generally in the immediate vicinity of the stomach, but very variable in appearance and general structure. Previously to the deposition of the spawn, the ovaries swell in a very remarkable manner, and the young Medusa, according to Blainville, are cast out through the mouth, sometimes after a certain degree of develop- ment in the appendages. In the Medusa aurita, according to Ehrenberg, the ova, previously to their maturation, escape through the peculiar aperture of the ovarian sac into the water, where they are laid hold on by the tentacula and the two layers of the brachial appendages, and received into little sacs which are formed on these layers, and which have a direction from the interior outwards. It is in these sacs that the ova are metamorphosed and matured. While in the ovary they have a thin smooth membranous envelope, are of a roundish figure, and filled with a dark-violet granulous fluid; but in the fetal sacs they have no shell, and present themselves under three distinct forms. Some resemble brambleberries, and their colour is a pale violet; others, also of a pale violet, are disciform, in shape like a miniature Medusa, without arms, and without nutritive canals; and the third, which is the most numerous, has a cylindrical form, truncated at both ends, and of a yellowish-brown tint. The last two are densely covered with cilia, and swim freely. The largest among them attain a diameter equal to the one-eighth of a line; and they are about one-third of this size when they lose their shell. From being unable to discover male organs in this Medusa, Ehren- berg has hazarded the conjecture that the smaller ova may become, as we understand him, males, which remain always of a microscopical size, while the females only grow large; but the conjecture is a bold one. We are scarcely able to reconcile these interesting facts with one observed by M. Saars. In a small volume published some years ago, this Swedish naturalist described a new genus of Medusidae under the name of Strobila, from its great similitude to a fir cone; but he now assures us that the Strobila is the young of M. aurita. In its strobiloid state it is composed of a series of circular pieces, with numerous tentacula, and the cone is surmounted by a cylindrical shaft; in its develop- ment the pieces separate successively into disciform ra- diated fragments, each of which becomes a perfect indi- vidual.

The growth of the Medusidae is as rapid as their life ap- pears to be short and transitory. There are many which never reach the magnitude of a pin's head; and thence they graduate upwards to a size, even in our northern seas, of fully two feet across the disc, with labial appendages not less than six feet in length. The bulk to which they occa- sionally grow in the Indian Ocean is immense; and were a

like hugeness attainable by them in the northern seas, we Acalepha might lend an easy belief to those naturalists who tell us that the Kraken was truly a Medusa. Mr Telfair saw a Medusa cast on shore in the Bombay territory in 1819, which must have weighed many tons. "I went to see it when the gale had subsided, which was not for three days after its being cast upon the sand; but it had already become offensive, and I could not distinguish any shape. The sea had thrown it high above the reach of the tide, and I instructed the fishermen who lived in the immediate neigh- bourhood to watch its decay, that, if any osseous or carti- laginous part remained, it might be preserved; it rotted, however, entirely, and left no remains. It could not be less than nine months before it entirely disappeared, and the travellers were obliged to change the direction of the road for nearly a quarter of a mile to avoid the offensive and sickening stench which proceeded from it."

The Medusidae abound in our seas during the summer and autumn, and are thrown ashore in heaps after every storm. Before the winter has set in they have dis- appeared, most of them being doubtless destroyed; but during the cold season some surely inhabit the deep recesses of the ocean, to reappear in another season; and it is prob- able that the spawn of one summer's generations lies hidden in the ooze, until revived and evolved by the heat of the coming summer. In tropical seas they are still more profuse, as well as more sportive in their configurations. Voyagers tell us of sailing through flocks so dense as to check the ship's progress, and expanding for miles over the surface; nor are they weary of speaking of their beauty and their phosphorescent and stinging properties. In the arctic seas these creatures are equally abundant, furnishing the giant whale with the material of his growth, and swarm- ing so thick, when of microscopic minuteness, as to com- municate their colour to the water. After his description of a globular semi-transparent species, from 1-20th to 1-30th of an inch in diameter, Dr Scoresby proceeds to say, "I afterwards examined the different qualities of sea-water, and found these substances very abundant in that of an olive-green colour; and also occurring, but in less quantity, in the bluish-green water. The number of Medusae in the olive-green sea was found to be immense. They were about 1-4th of an inch asunder. In this proportion, a cubic inch of water must contain 64; a cubic foot, 110,392; a cubic fathom, 23,887,872; and a cubical mile about 23,888,000,000,000,000. From soundings made in the situation where these animals were found, it is probable the sea is upwards of a mile in depth; but whether these sub- stances occupy the whole depth is uncertain. Provided, however, the depth to which they extend be but 250 fathoms, the above immense number of one species may occur in a space of two miles square. It may give a little conception of the amount of Medusa in this extent, if we calculate the length of time that would be requisite, with a certain number of persons, for counting this number. Allowing that one person could count a million in seven days, which is barely possible, it would have required that 80,000 persons should have started at the creation of the world, to complete the enumeration at the present time."

1 Probably the Oxyura medusina of O. Fabricius. Faun. Groenl. p. 257. 2 Ann. des Sciences Nat. n. s. iv. p. 297. Rathke apparently borrows his account of the development of the Medusa principally from Ehrenberg, but he omits their escape into the sea previously to their introduction into the brachial sacs, which is really incredible; and he says, that when lodged in these sacs they have no longer a chorion, as Ehrenberg pretends, and are consequently already young Me- duae. See Bardach's Traité de Physiologie, tome iii. p. 67, &c. 3 Ann. des Sc. Nat. n. s. vii. p. 248. 4 See Baster, Opusc. Subs. i. p. 25. 5 Edin. New Phil. Journ. iv. p. 406. 6 "They are sometimes thrown in great quantity upon the shores of our climate, where endeavours have been made to turn them to some advantage. It has been attempted, but without much success, to extract ammonia from them. They have been more beneficially employed in the way of manure upon arable land." Griffith's Curiosities, xii. p. 557. The Medusidae are all pelagic; but Professor Schwenke is said to have kept a species for six days alive in a basin of fresh water.—"ex Sparta fluvo haustis,"—a very wonderful fact, when we remember how instantaneously poisonous fresh water is to marine animals in general. Baster, Opusc. Subs. ii. p. 68. 7 Edin. Phil. Journ. ii. p. 12. Great numbers—for all of them are not so, as has been asserted—of the Meduside are phosphorescent animals, emitting their lights at irregular intervals; and the flame generally passes away after a short glow. The large species appear, when luminous, like globes of living fire floating on the surface, or shining at a great depth through the water; but when the species are small and crowded, the luminosity is diffused all round, or it is broken into innumerable spots of light, "rising to the surface and again disappearing, like a host of small stars dancing and sparkling on the bosom of the sea." The first kind of light is at least sometimes emitted at the pleasure of the creature, without the intervention of any foreign irritation; but the other two seem always to require for its elicitation some outward stimulus, such as is given by their mutual contact and friction when a fresh breeze curls the waves, or when an oar-driven boat or a ship passes through the teeming waters, when "a long train of lambent coruscations are perpetually bursting upon the sides of the vessel, or pursuing her wake through the darkness."

In such species as we have observed, the luminosity could not be detected issuing from any particular point or organ; it seemed that the whole body was impregnated with the light, which was given out involuntarily, if we may so speak; for some exterior irritation was necessary to produce the appearance of it, though the Meduse do not distinguish whether the annoyance proceeds from an animate or inanimate object. The species which possess the property are diffused through all seas, and the phenomenon is little less beautiful and interesting in the Hebrides than it is under the line, or in Australian seas. "The phosphorescence takes place, particularly around the tentacles, during the movements of the animal. Macartney saw it increased in the Medusa lucida when he warmed the water. The light also became more vivid in alcohol; the animals, however, quickly perished in it, and their light was extinguished. Spallanzani remarked the trickling of a viscous fluid from the surface of the Meduse, which had a burning taste, and produced an itching sensation on the skin. This liquid, mixed with water or milk, renders them phosphorescent for some hours, particularly when they are warmed and agitated. Dead animals, whose light was extinguished, again became phosphorescent by the addition of a quantity of spring water, and by movement at a heat of 26° to 37°. Humboldt observed his fingers to shine for some time after he had touched Meduse; he also saw the light become stronger when the animals were galvanized. The light of Meduse to which Macartney applied an electric shock was extinguished for an instant, but afterwards appeared more vividly than previously."

1 Baird in Mag. of Nat. Hist. iii. p. 309, and iv. p. 502. See also Thompson's Zoological Researches, p. 38, &c.

2 Some naturalists deny the luminous property of the Meduside ex toto, maintaining that the light is merely elicited by friction, &c., from some matter or fluid, with which the water is impregnated at the time. This opinion is ably supported by Mr Westwood in the Mag. of Nat. Hist. iv. p. 505, &c.; and for some observations confirmatory of this view we refer to the same work, v. p. 1, &c. The opinion however appears to us to be untenable, and is apparently disproved by the fact that Meduse have been noticed giving out their light at many fathoms depth, where they were beyond disturbance. "While sailing in the more shallow parts of the Caribbean Sea," says the Rev. Mr Guilding, "and looking over the vessel's side when becalmed in these dangerous waters, in the midst of reefs, I have seen at the bottom huge molluscous or radiate animals emitting the splendour of a lamp, but could never ascertain the species." Mag. of Nat. Hist. vii. p. 581. It were easy to quote similar facts, but a more conclusive one is this. We had a luminous Dianca in a glass of sea-water, and in a vessel of the same water we had, at the same time, a small specimen of Medusa aurita. The light was readily evoked from the Dianca, but we could obtain no light from the other vessel. It must therefore have proceeded from something else than the water. See in relation to this question the observations of Mr Bennet in Proceedings of the Zool. Soc. of London for January 1837; and those of his brother in the same work for June 13, 1837.

3 This is contrary to the assertion of voyagers, and it may be that our opinion is biased by our partiality to all that is native. Humboldt says, "The sea is phosphorescent in all latitudes; but he who has not witnessed this phenomenon in the torrid zone, and especially in the Pacific Ocean, can form but an imperfect idea of the magnificence of such a spectacle." See Edin. New Phil. Journ. v. p. 326. Dr Macculloch, during a voyage to the Shetland and Orkney Isles, discovered upwards of 190 luminous animals, of which the most conspicuous were about twenty small Meduse. Edin. Phil. Journ. v. p. 389.

4 Tiedemann's Comp. Physiology, i. p. 259. See also a summary of Spallanzani's experiments in Griffith's Cuvier, xii. p. 567.

5 Comp. Physiology, p. 269.

6 Hence they were named Utrice marinae by the older naturalists, and sea-metles by the common people. What Aristotle and Pliny meant by their stinging aculephes is very doubtful, as is shown by Kirby in Bridgman's Treatise, p. 402, &c.

7 Hist. Nat. des Vers, ii. pp. 163-4; also Griffith's Cuvier, xii. pp. 568.

Aclephus in museums. From these inherent difficulties, the classification of the Medusidae is believed to be still in an imperfect and artificial state; yet a comparison between its Linnaean barrenness, when one small genus embraced all the known species, and its present richness, when many genera are necessary to exhibit all its variety and fulness, affords a pleasing argument in behalf of the zeal and ingenuity of modern naturalists. Peron and Le Sueur, with a good knowledge of what had been done by others, and with much new information acquired in their voyages, were the first to attempt the orderly arrangement of the Medusidae; but it was found to be too artificially constructed, and has not been adopted by subsequent systematists.

Order 2.—ACALEPHINE VERE.

After the example of Macleay, we restrict the application of this term to some families of Arachnodermata, which, by their fantastic forms, are estranged from the typical tribes, and exhibit in their organisation such a variability among themselves, and such a mixture of the elements of more than one class, that their true position among animals is rendered doubtful; and we are fain, in order to preserve distinctness and precision to our definitions of the various classes, to set them aside as anomalous or annectant, or osculant groups, which, like corner-stones in a building, are adapted, by their very irregularity, to cement and gird the whole together. Most naturalists have believed them to bear the closest alliances with the Medusidae, more particularly with the Cirrhogrades; but Blainville deems them to have superior claims to a connection with the Mollusca.

A common character can scarcely be assigned to the order. They are gelatinous, nomadic, sometimes globular and radiated, more usually without any radiation, and deviating widely from familiar objects, so that we might compare them to the beautiful but misshapen orchideous and cryptogamous plants which blossom in the shades of the tropics, rather than to any animals which even the fancy of the herald-at-arms has yet pictured. Hence we shall distribute the little we have here to say of them under the two families which the order embraces.

The first family is named by Blainville Physogrades, an air-bladder being their principal organ of locomotion. Its general character is defined to be a regular symmetrical, bilateral, fleshy, contractile body, often greatly elongated, constructed with an air-bladder of greater or less size, which Blainville supposes, in the spirit of a transcendental anatomist, to be formed by a partial inflation of the intestinal canal, that has always a mouth and anus distinct from each other, and placed at the opposite extremities. The respiratory organs, according to the same author, reside in the lengthened irritable cirri attached to the body, and with which the ovaries are intermixed. The animals appear to have the power of secreting air, by which means the bladder can be filled more or less completely, and their buoyancy and position regulated according to their instincts. Whether the air is again absorbed when the floating Acalephes wish to descend, or whether it is ejected by compression from certain appropriate orifices, has been disputed. The latter is the common, and, as we believe, the correct opinion. A different opinion is however entertained by Dr Grant; for, after a storm of three days' endurance, he found many Velella cast on the shores of Cornwall, which should, on our hypothesis, have sunk to the bottom, and thus, in its stillness, have avoided the wreck which they suffered. But a fact which concerns the Velella alone, cannot be legitimately applied to the Physales, since the discrepancy in their structures manifestly prohibits such an application. With relation to the Physales, Mr Pescoock says, "on compression, air escapes from the sac by small orifices at each extremity." Mr Baird, who had many opportunities of making examinations of them, says of the same animals, "They have the power of contracting and dilating their membranous (air) bag at pleasure, and no doubt, by trimming it to the wind, make it act the part of a sail to propel themselves through the water. 'They are very often to be met with at sea,' says Sir Hans Sloane; 'and seamen do affirm that they have very great skill in sailing, and managing their bladder or sail with judgment for this purpose, according to the different winds and courses.' Upon attentively examining the narrow or free extremity of the bladder, a small round aperture is perceptible, surrounded by a circular zone of fibres, of a beautiful red colour, like the muscular fibres of the iris of the eye. Out of this small hole, which is not larger than would be sufficient to admit the passage of a very fine bristle, I squeezed the air out of the bladder."

The Physalus, a member of this order, is known to sailors as the Portuguese man-of-war, and almost every book of voyages into distant lands contains some account of its habits, mixed, as we may notice in the above extract from Sir Hans Sloane, with a little fable. One of the earliest descriptions of it is given by Clayton in his account of a voyage to Virginia, which we extract, because it is sufficiently descriptive, and gives the notions of the period regarding its nature. "In the sea I saw many little things which the seamen call Carvels. They are like a jelly, or starch that is made with a cast of blue in it. They swim like a small sheep's bladder above the water. Downwards there are long fibrous strings, some whereof I have found near half a yard long. This I take to be a sort of sea-plant, and the strings its roots growing in the sea, as duckweed does in ponds. It may be reckoned among the potential cauteries; for when we were one day becalmed, getting some to take observations thereof, the sportful people rubb'd it on one another's hands and faces, and where it touch'd, it would make it look very red, and make it smart worse than a nettle." Of the tentacula which hang from the lower edge there are two kinds; the longest being used by the Physalus for the capture of its prey, and capable of being coiled up within half an inch of the air-bladder, and then darted out with astonishing rapidity to the distance of twelve or eighteen feet, twining round and paralyzing, by means of an acrid secretion, any small fish within that distance. The food thus seized is rapidly conveyed to the short appendages or tubes, which are furnished with mouths for its reception. The creature is not only vesicatory, but luminous in a high degree; and we here remark, that these properties are probably common to every species of the family.

Of the other genera, all are remarkable for singularity of form. We might single out as among the most curious, the Rhizophysa, from its likeness to a bulbous root, with long radicular fibres, and the Physosphora, which imitates a root partly bulb and partly tuberous; the bulbous represented by the air-vesicles which are clustered above on a common stalk, and support the animal in an upright

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1 Annales du Muséum, tome xiv. 2 Mus. d'Actinologie, p. 112. This view has been adopted by Quoy and Gaimard, and by Lesson. Ann. des Sc. Nat. n.s., v. pp. 235-6. 3 Proc. Zool. Soc. Lond. iii. pt. i. p. 14. 4 Mag. of Nat. Hist. n.s. i. p. 598. 5 Mag. of Nat. Hist. iv. p. 476. Knowing Mr Baird's accuracy, we are disposed to receive his statement as correct; but it is opposed by Mr George Bennett, who states that he could never discover the orifice in question, nor expel air from the bladder without a puncture being previously made; and, moreover, that the partial escape of air from the bladder has no influence on the creature's buoyancy. See Proc. Zool. Soc. Lond. for April 1837, p. 43. 6 Phil. Trans. an. 1688, xvii. p. 783. 7 G. Bennett, ut sup. cfr. p. 43. 8 "M. Milne-Edwards believes that these (Physosphores) are not single animals, but the aggregation of a great number of individuals growing by buds, and living united together like the compound polypes. Ann. and Mag. of Nat. Hist. i. p. 166," position, while under them the stalk parts into many unequal tubers, whence depend the fibrilose radicles, which are the organs of respiration. The Apolemia and Stephanoidea, if possible, surpass this eccentricity of form; they are living clusters of sea-grapes or currants, with tentacles of curious structure pululating from amidst the berries.

The Diphyes, though less attractive, yet deserve notice from the view Cuvier takes of their organisation. He believes that each animal, as it is usually taken, consists of two different individuals, one being embossed in a cavity of the other; an arrangement which permits them to separate without destruction to individual life. The Noctiluca (Pl. VIII., fig. 4) is pre-eminent for its luminosity. It is a minute gelatinous spherical body, with a depression on one side, whence protrudes a sort of contractile stalk or proboscis; and we strongly suspect it is the same with the Medusa scintillans of our shores, better or more amply described and delineated. Mons. Suriray, to whom we owe our fullest knowledge of the Noctiluca, mentions that it seemed to have disappeared entirely from its ordinary habitats in the Channel during the period of the prevalence of the cholera at Havre, which was in the months of May, June, and July 1834. The fact is too remarkable not to be recorded, and seems to point to an atmospherical poison as the cause of that plague.

De Blainville gives to the second family the name of Ciliogrades, because they move about in the ocean by means of certain rows of vibratile cilia which garnish the body. They are gelatinous, translucent, fragile, very irritable and contractile animals, of multiform aspects, but always evidently binary or bilateral, although there are not unfrequently some signs of a tendency to radiation in their structure. Thus the genuine Beroids are egg-shaped or globular, girded longitudinally with eight ciliated bands equidistant or in pairs, so as to force a comparison between them and the Echinus with its ambulacral grooves. The alimentary canal is usually described as traversing the body from pole to pole, with an orifice to each, the interior and larger being the mouth, while the vent opens opposite in the centre of the apex. Near the middle of the body the canal is dilated into a stomachal cavity, at the sides of which the ovaries are usually to be distinguished by their vivid coloration; and from the same cavity there run two or more canals, which tend towards the tentacula, on the lower surface, and carry water to them; for their elongation and various movements are dependent on the propulsion of water into them from behind, or its reflux back within the stomach. The bands on which the cilia are placed run from the inferior or oral extremity to the opposite one, always in straight lines; they are of firmer consistency than the rest of the body, and are apparently formed by a duplication of the thin skin, so inserted as to leave a fine canal between their base and the surface. Through these canals there is probably a constant flow of water, and it has been suggested by Professor Grant that the play of the cilia may be maintained by this current, for muscular action for such a purpose seems to be inadequate. Our knowledge of their generation is very imperfect. Eschscholtz has seen minute Beroids, which even then had a close resemblance to their adult parents, but they were destitute of the eight rows of natatory lamellae. He could perceive in them only four Acalypia opaque longitudinal bands, which were probably the rudiments of as many rows of lamellae. These lamellae then are not developed until after the body has assumed the figure characteristic of the species; and of the eight rows which these all possess, it appears that at first there are only four, between which the others are afterwards produced.

The Ciliogrades abound in all seas, but many of them are rendered invisible to our dim vision by their pellucidity and small size. They move about with great alacrity, sometimes whirling on their own axis, or advancing forward obliquely, or rising to the surface and again quickly descending. As already mentioned, their principal organs of locomotion (and they are at the same time the organs of respiration) are the banded cilia, aided however by the contractility of the body itself, perhaps also by currents of water flowing through them, and in some genera (Ocygoes) by the undulatory movements of certain fin-like expansions peculiar to them. When they wish to repose, they poise themselves in mid-water by the aid of their tentacula, or by ceasing the play of the cilia; but motion, constant motion, is their joy and occupation. Their vivacity, their extreme delicacy and fragility, the purity of the tints which colour their internal organs, and their varying iridescence reflected from the surface by the changes and motility of their cilia, have made them the objects of admiration to every one who has seen them. The Beroid ovum is, in the estimation of Otho Fabricius, the most beautiful of the class, but so frail as to be injured and broken by the gentlest handling; and when we remember that their life is probably as transitory as that of the Ephemeridae, it does indeed require from their admirers all the philosophy of the poet to bid him say, unrepining,

"Oh! mourn not, that in Nature, transitory Are all her fairest and her loveliest things."

[The following is a summary of the Orders and Families of the Acalephae, according to modern views.]

Free swimming marine animals of a gelatinous or membranous tissue with thread cells. Digestive cavities or canals adherent to the surrounding tissues, and communicating with a more or less ramified circulating system. Most are dioecious, and pass by metagenesis through the forms of the monad and the polype, before acquiring the sexual acalypohoid character.

Order 1.—PULMOGRADA (Medusae).

(Discophora, Eschscholtz.)

Body discoid, with a marginal veil, and a mouth in the middle of the under side, which is usually extended into a more or less complex proboscis. A great central digestive cavity. Locomotion is effected by alternate expansions and contractions of the disc. Sexes distinct.

Sub-Order 1.—GYMNOPTHALMATA.

Eye-specks naked or absent; circulating vessels extending to the margin, quite simple or branched. Gemmiparous.

Fam. 1. Sarsidae.—Circulating vessels simple, 4; ovaries in the substance of the proboscis. Gen. Sarsia, Euphysa, Steenstrupia.

Fam. 2. Geryonidae.—Circulating vessels simple, 4; ovaries beneath the disc. Gen. Geryonia, Thaumantias, Slabberia.

Fam. 3. Circelidae.—Circulating vessels simple, 8; ovaries 8, beneath the disc. Gen. Circe.

Fam. 4. Aequoreidae.—Circulating vessels simple, 8, or more; ovaries linear on the course of the canals beneath the disc. Gen. Polyxenia, Stomotrichium, Aequoria, Phorcania.

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1 The Stephanoidea are, according to Lamarck, compound animals, consisting of a cluster of individuals which enjoy a common life and mutual communications through the medium of the central tube to which they hang. Anima. sans Vert. ii. p. 462.

2 Moseley, Zool. and Botany, i. p. 492.

3 The Vibrates of Chamisso; Beroides of Lesson.

4 The localities of Sheerness are familiar with the Beroid pilosa "under the name of the spawn of the sea-egg (Echimus), which it somewhat resembles in its globular and ribbed form." Grant in Trans. Zool. Soc. i. p. 9.

5 "I have generally found that the lively hues presented by the Acalepha depend on the bright opaque colours of their reproductive gemmules, which are often red, sometimes yellow, or brown, or purple." Grant in loc. cit.

6 This description has been lately pronounced by Mr. Forbes and Mr. Goodall to be inaccurate. They believe the supposed anus to be imperforate, and a great portion of the supposed intestinal canal to belong to the circulating system.

7 Grant et sup. cit. p. 12. Dr Fleming observed in Beroid ovum water moving in vessels along the middle of the bands to which the cilia are attached. The animals can change the direction of the currents in the vessels, and also the direction of the motions of the cilia. IV.—POLYPES.

The constituents of this class are in general animals of minute size, and of almost gelatinous consistency, characterized by having the oral aperture in the superior disc or extremity of the body, encircled with a row, or sometimes with several rows, of tentacular filaments. The aperture always leads into a cavity appropriated to the digestion of the nutrient matter, but in all other particulars the Polypes differ so widely in their organisation, that, to give a view of it which shall have any distinctness or use, there is a necessity to separate the class into groups.

It is an axiom, that no class of animals stands isolated but every one has its kindred claims on those around it. Thus it happens, that while Polypes have mostly felt the force of radiation in their development, they are not without their families that connect them with the unsymmetrical molluscs; and since it seems to us to be of importance that these relations should be remembered (for what study is more interesting to the zoologist than the mutual harmonies of two apparently remote classes?) we shall in the first instance divide the class into two sections, distinguished in a manner that brings this relationship into prominent view. The molluscan Polypes have both an oral and an anal aperture to the alimentary canal, and the tentacula that surround the former are filiform and ciliated; but the radiated Polypes have only one aperture to their digestive sac, serving by turns the purposes of a mouth and a vent, and the tentacula that guard it are not ciliated, but very contractile.

1.—MOLLUSCAN POLYPES.

Polyzoa, Thompson; Bryozoa, Ehrenberg; Ciliobrachiata, Farre.

The molluscan Polype is always a very small, almost a microscopic animal, with an elongated, slender, subcylindrical body, which is bent upon itself like a syphon, so that the two extremities approximate each other. The mouth is a wide edentulous aperture, situated in the centre of the circle of tentacula, which rise from its rim, and constitute a funnel-shaped coronet of extreme delicacy. The number of filaments of which the coronet consists is very variable, but each of them forms a long slender filiform tube, clothed on one side with vibratile cilia, by whose active and well-regulated movements a current of water is incessantly driven along them in one determinate direction. These currents not only supply a succession of unbreathed water to the animal for the purpose of respiration, but they carry in their stream the animalcular prey that the polype feeds upon. Under the tentacular coronet, the alimentary canal forms a kind of pouch analogous to the branchial sac of the ascidian mollusca, and, like it, plated usually in a longitudinal direction. From this pouch or pharynx the gullet descends a short space previously to its dilatation into the stomach,—an organ usually of an oblong shape, with its walls studded with spots of a rich brown colour,—apparently hepatic follicles, that secrete a fluid which often tinges the whole organ, as well as its contents, of a similar hue. The intestine, on departing from the stomach, makes a sudden bend, to which is suspended a large short caecal appendage; and afterwards the intestine proceeds upwards in a course parallel with the gullet to its termination, which is a little below the mouth, behind the pharynx, and on the side of the membranous sheath containing the tentacula.

This kind of polype is never found isolated and naked. It dwells enclosed in a calcareous or horny cell, of which a great number are placed in juxtaposition, usually after a quincunx pattern; and the entire congeries forms sometimes a leprous crust, sometimes a stony branched coral, sometimes a fleshy united mass, and at other times a horny flexible seaweed like polyplodum, or one that more nearly resembles some fine capillary moss or shrubby lichen. The numerous tenantry of these aggregations are besides all connected together, so as to form what has been named a "compound animal;" every individual capable of self-support and of continuing its kind, yet so connected with the rest as necessarily to participate in every good and every evil that affects the community. The polypes are so connected with their cells that they cannot leave them, for indeed the cell and polype are merely parts of the same body. This, such as it has been described above, is enclosed in a thin membranous sac; and the cell is formed by a continuation of this tunic reflected over the inner layer, and hardened by the deposition in it of calcareous or albuminous matter, to fit it to endure with impunity the contact and friction of the circumfluent waters, or to protect the soft viscera from accident, and from the access of their enemies. Milne-Edwards compares the cell to the lopt finger of a glove, which has had its open truncate extremity ornamented with a thready fringe, capable of being withdrawn by an act of involution within the finger-stool. The point of junction between the retractile portion and that which is not so, constitutes, when the finger or polype is withdrawn, an opening usually called the mouth of the cell, which is very often overhanging with a sort of moveable lip or valvular fold, named the operculum. Two muscular bands are attached to the inner surface of this valve, and their office is to draw it down and shut close the cell when the tenant has retired for rest or from danger.

The polyplodum, formed frequently of a congeries of many thousand cells, invariably begins with one only. This original or seminal cell has no sooner been completed (or even, in many instances, previously to its perfection) than another begins to shoot out from a fixed point of its parietes, the bud gradually enlarging and developing itself, until the form and size of the primary one has been attained. This process can most easily be traced in the common sea-mats (Flustra) and Lepraria, where, round the margin of the crust, cells can at all seasons be observed in every stage of Polypes, their evolution; one just budding, another half-formed, and others again nearly complete. They never begin their original in the body of the polype, but always from the parietes, or from the connecting medium of the cells; and it is not until these have made considerable advances to maturity that the polype becomes distinguishable within them.

From this mode of increase, there would seem to be no natural limits set to the magnitude and duration of the polypidom, except what arise from accident or exterior causes. The original polype and its immediate successors may grow old, languish, and die; but the solid cells remain in their connection as a root and fixture, while the newer races, which have sprung up towards the outskirts, continue their work, generation following generation in rapid and ever-multiplying successions. The polypidom in this respect resembles a tree in its growth: the trunk and main branches have stood years and centuries, but the increase has been made by annual shoots and renewals, and the last only know vigour and juvenescence. And as the form of the tree depends on the fashion of its ramifications, so that of the polypidom on the mode of evolution of its cells, for every part of the axis is not equally organised to produce buds, nor the same parts in all. Hence, if the primitive cell has only one point fitted for this generation, the polypidom will be built up in a catenated chain; if the cell has two points, two series of cells are formed, and in several the multiplication goes on in a regular arithmetical progression; but in others the cells are heaped together without apparent regularity, as in Alcyonella and Alcyoniumidium, where the softness of all the parts seems to allow of an irregular succession of buds. In this order, however, the general disposition of the cells is certainly after the quincunx, affording examples which the learned Sir Thomas Browne would have gladly adduced in proof that "Nature geometriseth and observeth order in all things, and of the generality of this mystic figure."

The molluscan Polypes are all hermaphroditical and oviparous. The ova, which originate in the organised medium connecting the individuals together, are lodged and matured within the cell in some families; but in others their matrix is a little pebble globe that is placed over the mouths of the cells, and often constitutes the principal beauty of the specimen. When ripe for expulsion, the ova are of a vivid orange or yellow colour, of a roundish shape, and clothed with vibratile cilia, by means of which they swim about to and fro in the water like beings endowed with volition, and scatter themselves abroad.

[It has already been stated, that the animals here called Molluscan Polypes are now generally dissociated by naturalists from the true Polypes, and placed under the name of Polyzoa, or Bryozoa, amongst Mollusca in the neighbourhood of the Tunicata. Dr Allman1 thus sketches the constitution of a Polyzoan: An alimentary canal, consisting of oesophagus, stomach, and intestine, furnished at its origin with long ciliated tentacula, with a single nervous ganglion on one side of the oesophagus; this canal is bent back upon itself towards the side of the ganglion, so as to bring the termination near the origin. The digestive tube thus constituted is suspended in a fluid contained in a membranous sac with two openings, one for the mouth and the other for the vent, the tentacula alone being external to the sac. By means of a system of muscles, the alimentary tube admits of being retracted or protruded at the will of the animal, the retraction being accompanied by an invagination of the sac, so as partially or entirely to include the oval tentacula within; the same process is traced in organs in the form of ovary and testis occupying some portion of the interior of the sac; no trace of a heart. The immediately investing sac has the power in almost every case of secreting from its external surface a secondary investment of very various constitution in the different groups. The entire animal repeats itself by gemmation, and thus produces one or more precisely similar Polypes, systems holding a definite position relatively to one another, while all continue organically united. The general arrangement may be seen from the following sketch of the POLYZOA.

ORDER I. PHYLACTOZOMATA.—Buccal disc bilateral; mouth with an arching valve-like organ (epistome). Sub-order 1. LOPOPEA (fresh-water).—Tentacles free or obsolete. Sub-order 2. PEDICELLINEA (marine).—Tentacles united at their extremities.

ORDER II. GYMNOLCEMATA.—Buccal disc orbicular or nearly so; no epistome. Sub-order 1. URNATELEA (fresh-water).—Only partially retractile. Sub-order 2. PALUDICELLEA (fresh-water).—Completely retractile; evagination of tentacular sheath imperfect. Sub-order 3. CYCLOSTOMATA (marine).—Completely retractile; evagination perfect; orifice of cell destitute of moveable appendage. Sub-order 4. CYENOSTOMATA (marine).—Completely retractile; evagination perfect; a circle of setae attached to the invertible portion, and acting as an operculum in the retracted state. Sub-order 5. CHEILOSTOMATA (marine).—Completely retractile; evagination perfect; orifice of the cell with a moveable lip.]

2.—Radiated Polypes.

The Radiated Polypes, or Anthozoa of Ehrenberg, present us with a greater diversity of structures than the molluscs. In all, the body is perforated superiorly with the larger circular opening into the digestive cavity, and surmounted with a coronet of tentacula; but the structure of the stomach, and the disposition of the tentacula, vary so much, that if our classification would follow and reflect a representation of the principal modifications of this variety, we are constrained to subdivide the class into three sections as follows:

(1.) HELIANTHOIDEA.—Polypes single or aggregate, free or permanently attached, fleshy, naked, or incrustated with a calcareous polydora, the upper surface of which is crossed with radiating lamellae; mouth encircled with tubulous tentacula; stomach membranous, plaited; intestine 0, anus 0; oviparous; the ovaries internal.

(2.) ASTEROIDEA.—Polypes compound, the mouth encircled with eight fringed tentacula; stomach membranous, with dependent vascular appendages; intestine 0, anus 0; reproductive gemmules produced internally. Polype-mass variable in form, free or permanently attached, carnose, generally strengthened with a horny or calcareous axis, enveloped with the gelatinous or creto-gelatinous crust in which the polype-cells are immersed, and which open on the surface in a starred fashion with eight rays.

(3.) HYDROIDA.—Polypes compound, rarely single, and naked; the mouth encircled with roughish filiform tentacula; stomach without proper parietes; intestine 0, anus 0; reproductive gemmules pululating from the body, and naked, or contained in external vesicles. Polydora horny, fistular, more or less phytoidal, fixed, external.

(1.)—HELIANTHOIDEA.

The typical representatives of this order are the Actinia or sea-anemones, which abound on every European shore between tide-marks, rivalling in beauty and vividness of colouring their floral namesakes. It is now well ascertained that the animals of the madrepores, sea-mushrooms, and brainstones of tropical seas, differ from the Actinia no otherwise in essence than in their power of excreting, from the inferior portion of the body, a large quantity of calcareous matter, the deposition of which under and around the body, and in the tissue of the folds formed by the tunics of the abdominal cavity, constitutes the cell or polydora, into whose hollows the tenant can partially or wholly retire. "The stony substances so formed are called corals, and their mode of formation causes them exactly to represent

1 A Monograph of the Fresh-water Polyzoa, including all the known Species, both British and Foreign, by G. J. Allman, M.D., Ray Society, 1856. On this subject the reader may consult Dr Johnston's History of British Zoophytes, 2nd ed., 1847, and Mr Busk's Catalogue of Marine Polyzoa in the British Museum, and various articles by the same writer in the Microscopical Journal.] the animal which secretes them; the upper surface is always furnished with radiating plates, the remains of the calcareous particles which were deposited in the longitudinal folds of the stomach before referred to; and as these plates do not usually reach to the centre, there is almost always a vacant space in the middle between them." The cells are either single and cupped, or they are branched like a tree, or they are aggregated together so as to resemble a cauliflower, or even to imitate the human brain; all these variations resulting from the manner in which the animal emits from the whole surface, or from a particular part of the sides of the body, the bud by which the new individuals of the general mass or society are produced.

The Helianthoida are all oviparous, the ova being produced in appropriate ovaries situated between the compartments formed by the septa that radiate from the outer parietes of the stomach to the skin. The ova are contractile and motile, being carried about from the action of the cilia that clothe the surface. "Under the microscope they prove of diversified form, many resembling flattened peas, some elongated or exhibiting irregular prominences, some almost spherical, and some which cannot be referred to any particular figure." After moving about for several days, during which their forms suffer some slight change, they insensibly relax in their motility, the cilia disappear, and having become stationary, each ovum rapidly runs through the stages of development that lead it up to the similitude of its parent.

The productiveness of the species and the rapidity of their growth are very great. The calcareous species often form enormous masses of coral, of the size of which we cannot judge by the specimens usually shown in collections, which are small individuals taken in the sheltered places among the rocks, where they are not exposed to the action of the waves, and collected before they have reached their proper magnitude. "The form of the masses appears to be greatly influenced by the positions in which they have grown, and the size of the individuals greatly depends on the quantity of nourishment they are able to procure. This is proved by the fact, that if all the individuals of the same mass are equally exposed, they are of an equal size; but if the surface of the coral is waved, as in the Explanaria, the individuals on the convex part of the mass, which could procure the most food, are large, while those in the concave or sunken parts are small."—J. E. Gray.

[The productions of the coral animal in the warmer parts of the ocean are not only wonderful in themselves on account of their vast extent and the minuteness of the animal by which they are created, but highly interesting for the light which they throw upon the history of the globe. On the north-east coast of Australia there is a reef 1000 miles long. The shores of New Caledonia are fenced in by a reef 400 miles in length. The coral islands of the tropical Pacific Ocean are innumerable, and are well known to all by the glowing descriptions of voyagers. These productions may be referred to three classes—molls, barrier reefs, and fringing reefs. The first consist of a circular wall of coral, rising from a solid base, surrounding a lagoon or sheet of mouldy water. The wall is seldom entire throughout, for there are places through which the water can find its way from the open ocean into the interior. The bottom of the confined water is usually cup-shaped, with a depth ranging from a few fathoms to fifty; whilst the outer side of the reef falls at an angle of about 45° to a depth of from 200 to 300 fathoms. In violent storms large pieces of the wall are broken off and driven into the interior cavity which thus becomes more or less filled up, and a low island is formed, to which floating seeds are carried that take root and flourish. A barrier reef only differs from an atoll in that it runs parallel with some large island or continent, from which it is separated by a broad deep channel. The outer side sinks at a steep angle into a deep ocean. The fringing reefs have only a narrow and shallow channel between them and the land, where the water on their outer side has small depth. Now it appears that the coral animal cannot live at a greater depth than thirty fathoms, and if exposed to the direct rays of the sun uncovered by water, it will perish. A consideration of these facts has led Mr Darwin to form a theory which has been generally accepted by scientific men. He believes that the phenomena in question are connected with movements which simultaneously affect large portions of the earth's crust, such as that by which the coast of Sicily is to the extent of some hundreds of miles, is now being elevated. He thinks that reefs have their foundation on land which has subsided, and part of which remains above the level of the sea; that barrier reefs show that the land, near which they are situate is likewise sinking; and that fringing reefs, on the other hand, denote that the land is either rising, as in the majority of the Sandwich Islands, where old reefs have been elevated to a considerable distance above the sea, or that the land is stationary. An examination of the chalk and limestone beds of the earth's crust shows that they are in great part composed of corals, all the species of which are extinct. Hence it may be conjectured that the labours of existing coral animals will remain to after-ages in the shape of calcareous beds, when the species themselves will have disappeared.]

(2)—ASTEROIDA.

The name of this order is derived from the starred marks that stud the surface when the polypes have contracted and hid themselves under the skin of the common mass or polypidom. These marks are produced by the incisures whence the tentacula are evolved; and hence the number of rays in each mark is mostly eight but sometimes only six in number, corresponding with the number of tentacula. These organs are, in this order, comparatively short, thick, and fringed or pectinated on the margins, and they radiate from a flat disc, in the centre of which the mouth is situated. This aperture is always circular, and leads by a gullet into a long cylindrical stomach, which is as it were suspended in a thin membranous sac or vesicle, and kept in its central position by eight or six septa or ligaments stretched between it and the vesicle, dividing the intermediate space into as many distinct compartments. From the inferior extremity of the stomach there hang eight or six twisted, intestine-like, but probably biliary, appendages, into a wide cavity, that communicates freely with the fleshy parenchyma by which the polypes are connected together, for the Asteroidea are all compound Zoophytes; that is, each species is a collection of numerous individuals participating in a common life, while each individual at the same time enjoys an independent vitality for every part of its body. The connection is effected partly through the medium of the skin, which is formed by the confluence of the outer thickened tunic of the polypes, and partly by aquiferous ducts that depart from the infra-abdominal cavity just mentioned, and permeate the entire mass in every direction.

The forms of the polypiferous masses are very various. Some are fleshy amorphous productions, covered with a coriaceous skin loaded with variously-shaped calcareous grains or crystals; others resemble a quill, and are called Sea-pens; others are like a rush or rod; while many, like the Gorgonia and Coral, are eminently imitative of marine vegetations. The internal part of the amorphous species is fibro-gelatinous; but when the axis assumes an erect or a branched tree-like form, the animals excrete in the centre of their body a more or less rigid support, which has been called their axis, and which has sometimes, though erroneously (from its being commonly seen in collections without the remains of the investing animal), been considered the entire coral. This axis is thickened by depositions of fresh layers of horny matter on its surface as the mass increases in size and requires more support, the increase of the thickness and length of the axis being always simultaneous with the growth of the mass."—(J. E. Gray.) In some genera the axis is bony, in a greater number it is of a horny nature, and very compact; in a few it is formed by the aggregation of siliceous needle-shaped spicula, and in others it is calcareous and stony; of which we have a familiar example in the red and black coral of the Zoophyte that furnishes the coral of commerce, so highly valued for ornamental purposes. In the genus Isis, "the axis has been considered as jointed, because the stony and the horny parts easily separate from each other when the mass Polypes.

of the animal has been removed and the axis is dried; but a larger and larger quantity of stony matter is gradually deposited as the mass increases in size, and in the large masses the axis of the lower part is almost entirely stony, like the axis of Corallium."—(J. E. Gray.)

The Helianthoida are all oviparous, and it has been affirmed that the sexes are distinct and separate. Dr Erdl of Munich says that he found in Veretillum only female individuals in one polypary, and in another only males; and he has convinced himself of a similar distinction existing in the genus Alcyonium or Lobularia. Plate X. fig. 9.

[The following is Milne-Edwards' arrangement of the Helianthoida and Asteroidea:]

CORALLIARIA.

Sub-class I. CNIDARIA.—Tentacles tubular, circularly arranged, and communicating freely with the visceral chamber.

Order I. ALCYONARIA.—Tentacles 8, pinnate.

Fam. 1. ALCYONIDE.—Adherent, without solid axis.

Sub-fam. 1. Ceriantharia.—Polyplidom increasing by budding, only basilar, and rising from stolons, or from a membranous expansion; sometimes isolated. Gen. Haimela, Cornularia, Clavularia, Rhizocoria, Sarcomictyon, Anthelia, Sympodium.

Sub-fam. 2. Tubiporina.—Polyplidom lateral, and forming arborecent tufts. Gen. Teletos.

Sub-fam. 3. Alcyoninae.—Polyplidom lateral, and forming simple lobed or branched masses. Gen. a. Alcyonium (Pl. X. fig. 9), Sarcophyton, Ammothea, Xenia; & Nephthys, Spogodes, Paracyclosium.

Sub-fam. 4. Tubiporinae.—Polyplidom composed of tubes with distinct walls, united by horizontal expansions. Gen. Tubipora.

Fam. 2. GORGONIDE.—Adherent, having a horny or calcareous axis.

Sub-fam. Gorgoninae.—Axis partly or entirely flexible, horny or cory, unjointed, of the same structure throughout.

Div. 1. Primnoidea.—Axis complete, dendritic; crust cory or smooth, axis horny. Gen. Eunicella, Gorgonia, Leptogorgia, Plexaura, Lophogorgia, Xiphogorgia, Rhipidogorgia, Hymenogorgia, Phaeogorgia, Physogorgia.

Div. 2. Gorgonellidae.—Axis complete, dendritic; crust cory, or smooth; axis calcareous. Gen. Gorgonella, Verucella, Ctenocella, Juncella.

Div. 4. Briaraceae.—Axis incomplete, and represented by a deposit of coryk tissue, or a mass of spicules. Gen. Briareum, Solanderia, Paragorgia, Cologorgia.

Sub-fam. 2. Tubiporinae.—Axis partly or entirely flexible, horny or cory, jointed with alternate segments of different structure. Gen. Mopsea, Melithea.

Sub-fam. 3. Corallinae.—Axis calcareous, stony. Gen. Corallium (Pl. X. fig. 3). See the art. CORALLUM.

Fam. 3. Pennatulidae.—Polyplidom free, with a central cavity which almost always contains an axis. Gen. Pennatula (Pl. X. fig. 8), Virgularia, Sarcophyllus, Pavonaria, Lituaria, Omphalina, Veretillum, Cavernularia, Renilla (Pl. X. fig. 11).

Order 2. ZOANTHARIA.—Tentacles simple or irregularly branched, their number increasing with age, generally more than 12.

Sub-order 1. ACTINIARIA.—No horny axis, integuments always soft (Pl. X. figs. 1, 1 a.)

Fam. 1. Actiniidae.—The tentacles of the different circles alternating with one another, each corresponding with a special perigastic cavity.

Sub-fam. 1. Minyadidae.—Integuments always soft, not forming a polyplidom; disc pedicellate, purse-shaped. Gen. Minyas, Plotactis, Nautactis.

Sub-fam. 2. Actinidae.—Integuments always soft, not forming a polyplidom; disc pedicellate, sometimes rudimentary, not capable of contraction into a purse; tentacles of one kind, simple. Gen. Anemonia, Eumenesides, Comactis, Comaster, Matridium, Drombus, Actis, Parasida, Capnea, Dynamis, Melactis, Corynactis, Heteractis, Cereus, Phymactis, Echinactis, Cyanea, Nemactis, Adamantis, Hyanthos, Sphenopus, Edwardsia, Pechia.

Sub-fam. 3. Thalassianthidae.—Characters same as those of Actinia, except that the tentacles are branched or bear papillae. Gen. Thalassianthus (Pl. X. fig. 4), Actinodendron, Actinaris, Phymanthus, Sarcophanthus, Heterodactylis.

Sub-fam. 4. Phyllactidae.—Characters same as sub-fam. 2 and 3, save that the tentacles are of two forms, some being simple, others multifid or dendritic. Gen. Phyllactis, Oulactis, Rhodactis.

Sub-fam. 5. Zoanthidae.—Integuments thickening and furnished with spicules, so as to form a leathery polyplidom. Gen. Zoanthus (Pl. X. fig. 2) Polythoa.

Fam. 2. Cerianthidae.—Tentacles in two concentric circles, one of the outer circle being opposite one of the inner, the two being placed over a single perigastic cavity. Gen. Cerianthus, Sacanthus.

Sub-order 2. ANTIPATHARIA.—Axis horny, with a fleshy or gelatinous coat, containing scattered spicules or mineral filaments (black corals). Gen. Cirrhipathes, Antipathes, Arachnopathes, Rhipidipathes, Leioctenes, Hyalogathes.

Order ACTINIOIDA.—Visceral cavity enclosing the stomach, and divided into compartments by perpendicular partitions of membrane, which support the reproductive organs; germs ejected through the mouth.

Sub-order ACTINIARIA.—Tentacles 12 or more; membranous partitions, sometimes simple, sometimes depositing solid calcareous plates, which, with the surrounding walls, constitute the coralium.

Tribe 1. Astraeinae.—Tentacles many in imperfect series or scattered; coralium, when present, calcareous, consisting of cells containing many radiating plates; the plates prolonged outwards beyond the cells that inclose them.

Div. 1.—Non-corallogeous families.

Base adherent at pleasure—

Tentacles compound .................................................. Metridiidae.—No European genera.

Tentacles simple—

Column pierced with loop-holes ........................................ Sagartiidae.—British Gen. Actinoloba, Sagartia, Phellia, Adamsia, Gregoria, Discosoma.

Column imperforate and smooth, Margin simple ......................... Antipathidae.—British Gen. Aiptasia, Anthea, Actinopsis.

Margin beaded .......................................................... Actinidae.—British Gen. Nemactis, Actinia, Phymactis.

Column imperforate, warted .............................................. Bassedidae.—British Gen. Tealia, Bunodes, Hormathis, Cystactis, Echinactis, Bolocera, Stomphia.

Base non-adherent—

Lower extremity rounded, simple ..................................... Hydrozoidea.—British Gen. Peachia, Hyanthus, Halecampa, Arachnactis, Cerianthus, Sacanthus.

Lower extremity including an air chamber ............................ Minyadidae.—No British species.

Order 2. CARYOPHYLLACEA.—Tentacles many, in two or more series; mostly increasing by lateral buds; generally depositing a coralium, which is invariably calcareous and many-rayed.

Div. 1.—No coralium.

Simple ................................................................. Caryophyllidae.—British Gen. Capnes, Aurellania, Corynactis.

Compound ............................................................. Zoanthidae.—British Gen. Zoanthus.] The Hydra, or fresh-water Polypus (Plate X. figs. 10 and 14), of which more has been written than of any other Zoophyte, is the type of this order, very remarkable for the extreme simplicity of organization of its members, and for their wonderful powers of redintegration and reproduction. The polype, considered independently of its polypidom, possesses no defined organs whatever; but when highly magnified, the whole body is seen to consist of a granular substance, the granules being loosely connected by a semi-fluid albuminous matter. On the upper pole of this gelatinous and very contractile body there is an aperture encircled with a variable number of tentacles, roughened with nodules, and extremely extensible, so that the creature can spread and stretch them far and wide in search of prey, which consists of very active crustaceous animalculæ and small worms. These are no sooner seized upon than they appear to be paralysed by some poisonous secretion of the polype, for their struggles and resistance are stopt as it were by magic, and they are carried unresisting to the mouth, and forced into the central digestive sac.

The Hydroïdae are reproduced by gemmules or buds, which are developed from the common substance of the body. In the Hydra they spring from no particular part, but in other genera they have a determinate origin, and in many others they are contained, like ova, in ovarian capsules, whence they are not discharged until ripe for evolution. But perhaps the most remarkable feature in the history of these Zoophytes, is their power of being multiplied by mechanical division. If a snip be made with a fine pair of scissors in the side of a Hydra, not only does the wound soon heal, but a young polype sprouts from the wounded part; if it be cut into two portions by a transverse incision, each soon develops the wanting parts of its structure; if longitudinally divided, both portions soon become complete animals; if it even be cut into several parts, every one of them will rapidly assume the form and functions of the original. The inversion of its body, by turning it inside out, does not destroy it; on the contrary, the exterior surface assumes the office of a stomachical cavity, and that which was originally internal will give birth to buds, and take upon itself all the properties of the skin.

The Hydra is locomotive and naked, but the majority of its order are permanently affixed to their sites, and are invested with a horny sheath or polypidom, which in many instances excels all other zoophytes productions in the delicacy and gracefulness of its form. These polypidoms are converfoid and more or less divided, the ramifications being divided in a variety of elegant plant-like forms. The stem and branches are alike in texture, slender, fistular, and almost always jointed at short and regular intervals, the joint being a mere break in the continuity of the sheath, without any character of a proper hinge, and evidently formed by regular periodical interruptions in the growth of the polypidom. Along their sides, or at the extremities, we find the denticles or cup-like cells, within which the polypes are contained, arranged in a determinate order, and either sessile or elevated on a stalk. Plate X. fig. 12. Though of the same substance, the cell is something more than a simple expansion of the stem or branch; for near its base there is a distinct partition or diaphragm, on which the body of the polype rests, with a plain or tubulous perforation in the centre, through which the connection between the individual polype and the common medullary pulp is retained.

[The researches of late years have shown that there is a very close relationship between the Hydroidea and the Aculephus. Many of the small free naked-eyed Medusa are in reality nothing more than the sexual apparatus of Zoophytes of the families Tubularidae and Campanularidae, from which they have arisen as buds, and then become detached, with separate locomotive and nutritive organs. In this state they are capable of existing and developing their sexual products, some possessing spermatozoa, others ova, thereby giving origin to a new generation of polypes. Again, the history of some of the larger Medusoids is essentially similar. Their progeny is at first polypoid, not taking the form of Medusa until a later period, and then, partly by budding from the polyp, and not by metamorphosis. Dr Carpenter's account of the process is this; the embryo emerges from the cavity of the parent, within which the first stages of its development have taken place, in the condition of a ciliated gemmule, of rather oblong form, very closely resembling an infusory animalcule, but destitute of mouth. One end soon contracts, and attaches itself so as to form a foot; the other enlarges and opens to form a mouth, four tubercles sprouting around it which grow into tentacles, whilst the central disc is drawn down to form the cavity of the stomach. Thus a hydra-like polype is formed, which soon acquires many additional tentacula; and this leads in every important particular the life of a Hydra. Under conditions not yet ascertained, this polype-like being ceases to propagate by ordinary gemmation, and enters upon a new series of changes. The body becomes more cylindrical, then a constriction is seen around it just below the ring which encircles the mouth; and similar constrictions appear below, the attached extremity, however, having the form of a fleshy bulb. The constrictions gradually deepen so as to divide the cylinder into a pile of saucer-like bodies, the edges of which become lobed. The topmost of these becomes detached and swims away; and afterwards the next, and so on, until the basal bulb only remains. Tentacles have meanwhile developed themselves on this bulb, which may return to its original mode of propagation by budding, and become the progenitors of a new colony of similar bodies, every one of which may, in its turn, throw off buds like itself. These detached discs have all the essential characters of adult Medusa. Each consists of an umbrella-like body, divided at its edge into lobes, and containing part of the stomach, which projects downwards like a proboscis, having a quadrangular mouth at the bottom. Further changes gradually take place, until the animal exhibits itself as a perfect Medusa, with sperm cells in the male and ova in the female. The embryos of the latter, after fertilization by the agency of the former, again go through the cycle already described.

These developments and changes induce some naturalists to place the Hydroida along with the Aculephus in an order called Hydrozoa. In giving a general view of the morphology of a Hydrozoan,

Professor Huxley describes the body as being essentially a sac composed of two membranes, an external (ectoderm) and an internal (endoderm). The cavity of the sac (the somatic cavity) contains a fluid charged with nutritive matter in solution, and sometimes, if not always, with suspended solid particles, which performs the functions of the blood in animals of higher organisation. The ectoderm is commonly ciliated, at any rate in the young; the endoderm is also very generally ciliated, though not always, nor in all parts. The cells of the endoderm, aided by the contractions of the walls of the body, are the sole means provided by nature for the circulation of the nutritive fluid in the Hydrozoa; the cells of the ectoderm, similarly aided by contractility, constitute the only respiratory mechanism. Notwithstanding the extreme variety of form exhibited by the Hydrozoa, and the multiplicity and complexity of the organs which some of them possess, they never lose the traces of this primitive simplicity of organisation; and it is but rarely that it is disguised to any considerable extent. The entire double-walled body of the Hydrozoan, whether it be a minute simple oval sac, as in the embryonic condition, or such a vast and complex mass as a tree of Plumularia, an Agalma 3 feet long, or a Rhizostoma of still more massive proportions, he terms hydrozoans, the simplest condition of which is that observable in the common fresh-water Hydra; one end of whose body is expanded into a kind of disc, whereby the creature adheres to its support, while the other extremity presents a widely open mouth, opening into a cavity which extends through the whole length of the animal, and surrounded by a circle of long tentacular organs.

The following is Professor Huxley's arrangement of the families constituting the Hydrozoa:

1. Hydroidea. Hydra (fresh-water.) Coryne, Corymorpha, &c. Sertulariaceae. Plumularia, &c. Calycophoridea. Diphyes, Galeolaria, Abyla, Sphenocentra, Praya, Hippopodius, Voglia. Diphyozoaidea. Eudoxia, Eudoxoides, Aglaisioides, Sphenoides, Cuboides, Amphora, Euneagonoides. Physophoridea. Apolema, Halistemma, Forskalia, Stephonoma, Agalma, Physophora, Athorybia, Rhizophysa, Physalia, Velella, Porpita. Lucernariidae (placed by Milne Edwards amongst the Corallaria). Medusidae. Medusa, Ajanma, Pelagia, Cassiopea, Rhizostoma, &c.

The British genera, constituting the second and third of these families, may be thus arranged:

Tubulariidae. Naked deciduous germs, springing from near base of tentacles—Clava, Vorticella, Hydractinia, Myriothela, Coryne, Eudendrium, Tubularia, Corymorpha.

Sertulariidae. Egg-germs inclosed in vesicles; animals increasing by permanent lateral buds, polypes in cup-like sessile cells—Halecium, Sertularia, Reticularia, Coppinis, Thaliaria, Antennaria, Plumularia.

Campanulariidae. Characters like the last, except that the polype cells are stalked—Laomedea, Campanularia.]

V.—RHIZOPODA.

The name Rhizopoda was bestowed by Dujardin on a division of the animal kingdom very low down in the scale of organisation, on account of their capability of throwing out root-like processes (pseudopodia), which are retractile at will, into the body of the animal, and which serve them as a means of locomotion. The class is a portion of that composite order named Protozoa, into which Sponges fall. Rhizopods are minute animals living in fresh or salt water, and usually free. As far as research has gone, they are destitute of all organs whatever, possessing neither mouth, stomach, muscles, nerves, cilia, circulating system, nor generative system. They consist of a mass of gelatinous flesh denominated sarcod, parts of which can be extended either in the shape of finger-like processes or of delicate threads. Their modes of supplying themselves with food is, in the majority of species, by contracting their pseudopodia, and drawing into the exterior of their bodies the particles of aliment which have become entangled with them. There they undergo some sort of digestion, the useless portion being afterwards rejected, passing, as before, through the very substance of the animal. Whilst ciliated gemmules are thrown off by the sponges, which subsequently become converted into bodies like the parent mass, nothing of the sort has been observed in the Rhizopoda, where the only mode of propagation known is that by self-division.

The class Rhizopoda may be divided into the following groups:

A.—Rhizopoda amorphia.

1. Naked Rhizopods. 2. Rhizopods with a membranous or coriaceous envelope.

B.—Rhizopoda polythalamia.

3. Rhizopods having a calcareous or arenaceous shell (Foraminifera).

C.—Rhizopoda radiolaria.

4. Rhizopods furnished with silicious spicula, or shells, including the Polycystina.

1. To the division of naked Rhizopods belong the microscopic animals named Amoebae and Actinophryes. The former, found in fresh and stagnant waters, is a shapeless mass of sarcod, the outer layer of which has a slightly denser consistence than the internal semi-fluid matter; but it scarcely proceeds so far as to form a distinct membrane or capsule. Within are vesicles and vacuoles, one of which can be seen to pulsate at nearly regular intervals. Another evidence of vital activity is exhibited by the change of form which it goes through in moving from place to place. This operation is performed by pushing out finger-like projections, then causing the body to follow, as it were, to enter the space left by the parts so extended. If alimentary particles are met with, they are enveloped by the animal's body, which they are made to enter, and the indigestible portions are ultimately rejected. It has been found that pieces cut off from the animal are capable of shaping themselves into independent beings. The Actinophryes has a rounded body, of a constitution pretty much the same as that of the Amoeba, but it is usually seen with radiating needle-shaped pseudopodia, which can be withdrawn into the body.

2. Of the Rhizopods with a membranous coat, the genera Gromia, Difflugia, and Arcella are examples. Here an advance in structure is seen, and there is usually some regularity of shape. In the two latter genera, a few finger-like projections of the sarcod body are put through orifices in the coat, with a view to collect food. The basis of the envelopes appears to consist of a horny substance resembling chitin; the surface is ornamented either with spines similar to those in the Desmidaceae; or at other times with circular markings, like those seen on the Diatomaceae. In Gromia, the pseudopodia are filamentous and much more numerous, being emitted both from a portion of the sarcod body extended round the outside of the coat, and through an opening from the interior, where the main mass of the animal lies.

3. A much more interesting group of Rhizopods is that of the Foraminiferae, where the animals are protected by a calcareous or arenaceous shell, forming beautiful objects for the microscope. This group, which derives its name either from the foramina connecting chamber with chamber, or from the foramina wherewith the surfaces of the shells are generally pierced, has received much attention from naturalists of late years, on account of their comparatively large size, the usually elegant forms of their envelopes, and the vast abundance of their remains in a fossil state. They are all marine, and specimens may be collected from every coast. Fifty-seven species have been described as British. Certain species abound in seaweed on the shore, others have been dredged from great depths of sea. Their shapes are very varied; some are flat discs; others of an elongated form are straight, curved, flask-shaped, or resembling a string of beads; others again are ovoid or globular; whilst many are extremely like the shell of a nautilus, on which account they were once ranked amongst the Cephalopods. The majority have smooth calcareous shells, but some have rough arenaceous envelopes. Some species are attached to foreign bodies, but the greater part are free. In the species having a globular shell, it consists of a single chamber; but it is all but the universal rule for the shell to possess more than one chamber. In this case the chambers are connected, and the animal occupies every chamber, even where there are hundreds (as in the genus Orbitolites), thus differing from the Nautiluses, which only occupy the exterior chamber of its shell. The variations which the shells of the same species undergo are so great, that classifiers are extremely puzzled where to draw the line between species and species, even between genus and genus; and they have been tempted to think, when specimens collected from different parts of the globe are under examination, that specific distinctions have no existence amongst the Foraminiferae. The same species being able to live, by reason of its low organisation, under very different circumstances, to climate, depth of sea, &c., variations in form cannot be expected. The substances to which certain species attach themselves—shells, rocks, seaweed, &c., will also entail variety of form. The shells of some species are totally devoid of structure, whilst those of others abound with tubuli in their walls. The mode in which the chambered forms increase their size seems to be by a process of budding, the gemmules becoming coated with calcareous matter, and thus making a new chamber. The direction of the growth will, of course, determine the form of the shell. When segments are continually added spirally in the same plane, the result will be, if the additional chambers are of the same dimensions, a disc; if they increase in size, a nautiloid shell. If, however, the spiral growth takes place a little to one side, a trochoid or pyramidal form will be produced. On the other hand, if the chambers are added in a straight line, there will be a rod-like, or dagger-like form. As to the mode of propagation, nothing is known, save that, in some species, it has been observed, when a portion has been accidentally broken off, it has gradually grown into a complete animal.

Alcide D'Orbigny undertook an elaborate examination of the Foraminiferae, and formed an arrangement of them founded on the structure of their shells. Later naturalists, however, have seen reason to be dissatisfied with his arrangement, insomuch as the shells of the same species vary extremely, so that not only may a gradual transition be often traced from one of D'Orbigny's species to another, but varieties of the same species would fall into different genera. Dr Carpenter is now at work on the subject, and has published various papers in the Philosophical Transactions. The scientific world is, however, expecting from him a general account of the class, with a more reliable arrangement, than any extant. In the meantime, Professor Williamson of Manchester has described a figured shell of British Foraminiferae, and Mr. Macgillivray has printed several valuable memoirs on the subject in scientific periodical works. In our present ignorance as to the limits of genera, it would be useless to give a list of those which have been proposed.

Fossil Foraminiferae.—A few species have been found in Lower Silurian beds. The species increase in number as we advance towards the present time. In the chalk they are plentiful, and the number of individuals in certain localities is prodigiously great; so much so, that the bulk of some beds is composed of them. In tertiary strata they are still more abundant. In the Paris basin there are some beds of a stone employed in the buildings of that city, and known as the Milliolite limestone, which is composed entirely of foraminifera. The great eocene formation, termed nummulitic, which occurs in every quarter of the globe, has sometimes been of 1800 feet, and often attains a thickness of several thousand feet, abounding with the genus Nummulites, of which more than fifty species have been described. Nummulites belongs to a highly developed type of foraminifera, and some species are as large as a crown piece. This formation enters into the composition of many great mountain-chains, including the Alps, Pyrenees, Carpathians and Himalayas; in which last range nummulites have been collected at a height of 16,000 feet above the sea. The pyramids of Egypt are built of this limestone. As Nummulites are characteristic of eocene strata, the genus Amphistegina is characteristic of miocene beds, in which it has been found in the Vienna basin, in St Domingo, at the Madeiras, and elsewhere. Lamarck has truly said that these minute animals have had much more influence in building up the crust of the globe than the remains of elephants, hippopotami, and whales.

The Rhizopoda radiolaria have been divided by Johannes Müller ("Memoir on the Thalassicollis, Polycystinae, and Acanthometrae of the Mediterranean," Trans. Royal Acad. Sci., Berlin, illustrated with eleven plates, 1853), into the following sections:

§ Simple.

1. No shell; naked, or with scattered silicious spicula. Thalassicollis. 2. With silicious reticulated shells. Polycystinae. 3. No shell; but furnished with silicious radiating spicula. Acanthometrae. VI.—SPONGES.

*Spongia; Spongidae; Porifera; Amorphozoa.*

The Sponges differ so much from all other Zoophytes, that De Blainville has constituted with them a separate class, under the denomination of *Amorphozoa*, to mark that want of a definite and constant form in their species for which they are remarkable in the animal kingdom. Their general appearance and structure must be familiar to every one. They are soft, elastic, porous or cellular bodies, of a uniform structure in every part, without any organs or vessels, and capable of absorbing large quantities of liquid, which they again yield up on pressure, without injury to their textures. They are quite insensible to every sort of irritation, and can contract neither the body as a whole, nor any portion of it; nor can they remove in any way from the site on which they have grown.

In a recent state the sponge is filled with a colourless animal jelly, the quantity of which varies much in different species. This jelly is apparently homogeneous; but, with the assistance of the microscope, it has been discovered to be full of numerous transparent spherical granules. It is diffused through every part of the sponge, filling the intercellular spaces, and it lines also the canals which permeate the mass, and often covers the surface with a slimy coat.

The sponges used in domestic economy are composed of a horny fibre, netted together so as to form small irregular meshes, with larger canals and holes interspersed. The fibre is solid and transparent, generally smooth, but sometimes closely invested with a fine branched vascular tissue. These sponges are soft, compressible, and eminently bibulous; but there is a gradual passage from them into others of a more rigid and compact texture; and on examining into the cause of this change, we find that the fibre has become loaded with crystalline needle-shaped spicula, which, chemical tests assure us, are formed of pure silex or flint. There are many sponges in which these spicula predominate so far that the horny matter has become of secondary importance; and such sponges, after being dried, resemble crumbs of bread, and are easily rubbed down into a powder merely by friction between the fingers. Dr Bowerbank has shown that the transition from the fibro-horny to these silicious sponges is insensibly made, and that many species, which were believed to be purely fibrous, contain in fact numerous minute imbedded spicula.

There is another class of sponges, rather of a felted than reticular structure, and containing a very scanty proportion of organic fluid. They are usually of a grayish-white colour, and are loaded with spicula, but the spicula are composed of carbonate of lime. These spicula are more variable both in form and size than the siliceous kinds; for in the same sponge we often find some which are needle-shaped, others that are club-shaped, and others that are formed of three or four divergent prongs. There has not been discovered any sponge in which the calcareous and siliceous spicula naturally co-exist; but some species of a compact fleshy texture have been described, in which, while the central parts are crammed with spicula of flint, the surface is covered with a layer of calcareous earth.

In all sponges the surface is porous, and of a finer and closer texture than the interior, which is also permeated with some irregular sinuous canals, that open on the surface in the form of circular orifices, which have been called their *oscula*, but which are properly their vents. When living and in health, the sponge is continually imbuing by the pores the water which surrounds it. This water, penetrating to every part, fills the cells and distends the body equally; it is then forced into the canals, and driven, in an agitated current, from the body, through the oscula. By this circulation the air and food of the sponge is supplied, and its effete excretions removed; but by what agency it is originated and kept up is not positively ascertained. Dr Grant thinks it probable that minute vibratile cilia planted in the canals and pores are the moving power; while Dutrochet ascribes the phenomena to that law of endosmosis which he has discovered to regulate the transmission of liquids of unequal densities through all organic membranes.

Sponges are propagated by gemmules, which originate in the organic mucus, and are carried out of the body by the effluent currents just described. In some sponges these gemmules are ciliated and locomotive when mature; but it seems probable that the majority of the species produce only unciliated gelatinous grains, which are nevertheless endowed with a very active motility, like the ultimate particles of even inorganic matter.

With one or two exceptions, sponges are natives of the sea, ranging from tide-marks to a very considerable depth. They are scarce and small in cold latitudes, and gradually increase in size and numbers as we trace their course towards the tropics, but perhaps they abound most of all in the genial seas of the Australasian islands. The sponges of commerce are chiefly procured from the Mediterranean, and from the Bahama islands in the West Indies.

*Spongiella* is the only fresh-water genus. Dr Bowerbank has been for some years past engaged in the examination of the *Spongidae*, and has begun to publish a series of valuable memoirs, in which their anatomy and physiology will be minutely described, as a foundation for an entirely new classification of the genera. The generic characters will be principally built upon the organic structure and mode of arrangement of the skeleton, as it has been found that neither their external form nor their chemical constituents will afford any clear or sound general views. According to Dr Bowerbank there are twenty-four genera of sponge on the shores of Britain, viz., Tethya, Geodia, Pachymenidae, Halichondria, Hy- meniacidon, Hallina, Isodictya, Desmiderae, Rhyynchia, Didemnum, Hallicona, Microciona, Hymersphia, Rhyndesmia, Halyphysma, Euplectella, Hallocnema, Phakellia, Dyckia, Spongia, Granita, Leucosia, and Leucosolenia. The forms of the spicula (which are very various and afford beautiful microscopic objects) have been described in a memoir printed in the *Phil. Trans.* for 1853. The same author has written various papers on the vitality, ciliary actions, &c., of the *Spongidae*, and on the organisation of particular species, which have been printed in the *Trans. Micr. Society*, or amongst the *Reports* of the British Association. Dr Johnston's *History of British Sponges* may be referred to for an account of such species as had been observed on our shores some years back. Dr Grant's papers, in the 13th and subsequent vols. of the *Edin. Phil. Journal*, contain valuable matter. Lamarck's arrangement, in the 2d vol. of the *Animaux sans Vertébrés*, is quite obsolete.] VI.—LITHOPHYTES.

(Corallinaceae)

The Lithophytes, in the restricted sense in which we use the term, are plant-like marine organized bodies, which adhere to other substances by a crustaceous base, and are composed of an internal fibrous axis incrusted over with a chalky porous bark, either continuous, or divided by septa into numerous equal articulations. From the time of Ellis, who was a strenuous advocate of their animality, they have been always described as members of the animal kingdom; but the observations of Blainville and Schweigger leave no doubt of their being truly vegetables, differing little from many algae.

There are two families of Lithophytes. In the first the calcareous crust is rather thick, compact, or minutely porous, and jointed. The family corresponds exactly with the genus Corallina of Linnæus, subdivided by Lamarck and Lamouroux into the following genera:—Cymopolia,

Corallina, Jania, Flabellaria, Amphizoa, Penicillus, Galaxaura, Acetabulum, and Polyphysa. Many of the species are very pretty, and the Acetabulum is a parasol in miniature. Plate X., fig. 13. One species (Corallina officinalis) has been much celebrated as a powerful vermifuge.

[In Halimedes, as well as in some of the preceding genera, the fronds are articulated; but in Nudipers and Melobesia, the plant appears like a simple crust adhering to rocks on the shore. Carbonate of lime is deposited so plentifully in the tissues, that the whole has the consistence of stone. By treating these plants with dilute acid, the lime may be removed from the vegetable tissues.]

The second family, from being more decidedly vegetable in its aspect, is named by Blainville Fucoidæ. In it the cretaceous crust which covers the stem and branches is very thin and continuous, and it offers to observation no trace of pores. The organic substance is also more gelatinous, and consequently approaches nearer to that of the true seaweeds. The genera are, Udotea, Dichotomaria, Liagora, and Neomeris.

(Z. J.) (J. Y. J.)