HELMINTHOLOGY.1

HELMINTHOLOGY.¹

(ANNELIDA.)

THE title of this article was formerly bestowed on a much larger group of animated beings than that to which it has been here restricted. The Linnæan group of Vermes contained, in fact, the whole of the intestinal and other worms, the molluscous and testaceous tribes, the Zoophytes and Infusoria—which now form the natural materials of many classes. We here apply it exclusively to the ANNELIDA, or red-blooded vermes, of which the medicinal leech and earth-worm afford familiar examples. Brugière and others have no doubt conjoined them, in comparatively recent times, with the intestinal tribes; and it was at one time our intention (see ANIMAL KINGDOM, § Divisions) to have adopted that arrangement. But we conceive it to be more in accordance with the principles adopted in our other systematic articles, to abide by the example of Cuvier, and, referring the latter to the radiated or zoophytical division, to include in the article HELMINTHOLOGY the Annelida alone. In truth, the intestinal tribes exhibit no organs of respiration, either tracheal or branchial—no traces of a true circulation—and their nervous system is extremely obscure. It will therefore become apparent, from the following definition, how greatly the Annelida differ from the creatures just named.

The Annelida or red-blooded worms form the first class of the articulated or annulose division of the animal kingdom.² Their blood, of a red colour, resembling that of the vertebrated

animals, circulates in a double system of closed vessels, that is, in arteries and veins. This system, though destitute of a heart properly so called, is sometimes provided with one or more distinct fleshy ventricles. Respiration is carried on through the medium of organs, which are sometimes external, occasionally developed beneath the surface of the skin, or sunk more deeply into the interior. They may all be presumed to breathe by means of branchie, although the respiratory system of the so-called Branchial Order is still in some respects obscure. The branchie or respiratory organs of the greater number are external, and vary considerably in their size, form, number, and position. Their body, of a softish texture, is more or less elongated, and always divided into numerous rings or segments, of which the anterior, known under the name of head, scarcely differs from the others, except by the possession of a mouth, and of the principal organs of the senses. None of the Annelida possess articulated members properly so called, but in room of these many are furnished with setiferous mammillæ, or fleshy projections, bearing bundles of hairs or bristles, and forming what may be called pedes spurii, of which the number is extremely various. These peculiar organs are sometimes composed of two parts, the one superior and dorsal, the other inferior and ventral. The muscular power resides in the interior, and is capable of producing only an undulatory or creeping movement—

¹ From Ἡλμιν, a worm, and λόγος, a discourse.

² For a description of these primary divisions of the animal kingdom, see ANIMAL KINGDOM, § Third Primary Division.

Annelida. the locomotive parts being incompetent to sustain the body. The organs of the mouth consist sometimes of parts resembling jaws, more or less developed, sometimes of a simple tube. The organs of the external senses are composed of fleshy tentacula, sometimes articulated, and of certain blackish points, not existing in all the species, regarded as eyes. The nervous system consists of a double ganglionic cord, analogous to that of insects, as already described in our art. ENTOMOLOGY. In regard to their natural habits, most of these creatures are aquatic (the Lumbrici or earthworms excepted), and a great majority marine. Some dwell in holes beneath the waters, others form tubes or tunnels of mud or other matters, or even transude from their own bodies a calcareous secretion, which forms around them a protecting covering.¹ Considered sexually, they are for the most part hermaphrodite, and some require reciprocal communication.

It will be perceived, even from the preceding brief exposition, that the Annelida are animals of a very peculiar nature. Although their nervous system coincides with that of the other articulated classes, and although their bodies are likewise divided by transverse sections, yet their locomotive organs are entirely dissimilar to those of the Crustacea, Arachnides, and Insects. Their setiferous mammillae are merely retractile sheaths; and the hairs or bristles which they inclose are in no way comparable to the feet of the last-named classes, but are organs of a very different nature.

The Annelida are few in number compared with insects and other articulated classes, and the greater proportion are marine. Their possession of red blood is a singular character in animals so low in the scale, and one not possessed by the molluscous tribes, which are yet regarded as their superiors in other points of organization. Some peculiarities in the circulating fluids of these creatures have been recently described by Dr Williams.² With the exception of one or two species, two distinct and separate fluid elements of nutrition exist in these creatures—one, consisting of the proper and true blood, is contained in closed vessels, and moving in a definite orbit, constitutes a well-marked circulation; the other is a liquid mass, filling the open space which, in all species, intervenes between the intestine and the integument, holding organic corpuscles in suspension, varying in different species, and performing irregular to-and-fro oscillations under the agency of the muscular contractions of the intestine and integuments. On these two fluids two separate physiological functions devolve, each essential to the maintenance of life in the Annelida. All the recesses and ramifications of the general cavity of the body in these animals communicate freely with each

other, constituting thus one common space. This cavity is lined by a distinct membrane, which is obviously the anatomical analogon of the peritoneum, and is filled by a fluid which is unquestionably an organic fluid. Dr Williams adduces reasons for regarding it as physiologically allied to the chyle of the higher animals, and the containing cavity as the prototype of the peritoneal. This general splanchnic chamber he therefore names the peritoneal cavity, and its liquid the peritoneal fluid, or the chyle-aqueous fluid of the peritoneal cavity. As the peritoneal membrane of the Annelida is not vibratory, the oscillations of the fluid contents cannot be caused by ciliary vibration. This fact is regarded as distinguishing the class from the Echinodermata, of which, in all the species, the peritoneal space is richly lined with vibratile cilia. The real character of this fluid was till recently unknown. Its coagulating principle consists of fibrin, and there can be no doubt that the greater portion is composed of sea-water. In a few minutes after removal from the body of the animal, it throws down an unquestionable coagulum, like the clot of true blood. The organic corpuscles cohere into groups and masses, and sink with the clot. Mechanically and physiologically this fluid is immediately essential to the maintenance of life—mechanically, by preventing contact between the intestine and integument, thus favouring the circulation of the blood proper; and physiologically, by furnishing the pabulum out of which the latter fluid is perpetually renewed or reinforced. In the genus Sabella this peritoneal fluid is opalescent and thickly corpusculated; it does not change its colour with that of the true blood, since its colour is the same in those species which are distinguished by green blood, as in those of which the blood is red, although so generally charged with corpuscles. Aphrodita aculeata is an exception, and exhibits a fluid which, bearing no visible morphous substances, seems to depart but slightly from the standard of salt water. The physiological character of this fluid is unequivocally manifested in Glycera alba, in which it bears in great abundance blood-red flattened oval corpuscles, resembling those of the frog. This is the sole instance of an Annelid with coloured corpuscles in the peritoneal fluid. The blood proper in this species is so faintly red as to be nearly devoid of colour, and is quite incorpuscular.

That the basis of this fluid consists of sea-water is rendered almost certain by the following expedient. If it is collected in adequate quantities (say from Arenicola or Terebella nebulosa), and carefully filtered, and the clean liquor then submitted to evaporation, the crystalline products will be found identical with those resulting from the evaporation of simple sea-water. Dr Williams infers

¹ "As to the external tube which the Chetopoda (by which term M. de Blainville denominates the setiferous genera of the class Annelida) often inhabit, although it is frequently sufficiently regular and solid, it cannot however in any manner be compared to the shell of the Mollusca, not even where there is the greatest approximation, as in Dentalium and Silicaria. These tubes of the Chetopoda are always simple excretions from their body, which are by no means attached to it, and from which the animal may issue forth without dying immediately. We begin to observe something of this kind in the mucosity with which certain species line the hole hollowed in the mud or sand which they inhabit, as in the Arenicola, and some Lumbrici. This is analogous to the mucous pellicle of the tube of the Amphitrite and the Sabella; but in the latter, surrounding this mucosity, is attached externally a stratum, more or less thick, composed merely of mud or very fine grains of sand, or, in fine, of debris, more or less thick, of shells and larger grains of sand. These tubes are constantly open at both extremities; there are also some of them more regular, which are completely calcareous. The double opening is a character whereby they are distinguished from tubular shells, the summit of which, on the contrary, is constantly imperforate. These tribes, however, appear constantly to grow, after the manner of tubular shells, by lamina or strata extremely thin, placed inside of and out-edges one another. From this result arise, marking the growth, more or less apparent outside; but we never remark longitudinal striæ on their surface, nor anything indicating the delicate working of the edges of a mouth, as in the Mollusca. This character alone might suffice to distinguish them from the true tubular shells; but to this we may add, that the constant perforation of the summit of the tube of the Chetopoda never allows the animal, in growing and advancing in its tube, to form partitions there, whereas in the tubular shells the reverse is invariably the case. A final character which distinguishes the tubes of the Chetopoda is, that they are adherent, and fixed flatly, through a greater portion of their extent, on foreign bodies, which never takes place with the tubular shells." (Griffith's edition of Cuvier's Animal Kingdom, vol. xiii., p. 58.) We may add, that the young of the shell-bearing Mollusca are always born with shells, because that part forms, in fact, a portion of their skin; but there is no doubt that the young Annelida are produced in an exposed condition, and afterwards proceed, by a voluntary effort, to form their protecting habitations.

² See his excellent and elaborate paper "On the British Annelida," published in the Reports of the British Association for 1851. London, 1852.

Annelida, that this sea-water, under such circumstances, readily assumes the character of an organic fluid—that is, becomes vitalized with great facility by the solid organic elements contained in the peritoneal fluid. Whether the peritoneal fluid is organically capable of maintaining the nutrition of the solid structures of the system, cannot be directly proved; but it is scarcely susceptible of doubt, from the intricate manner in which the true blood-vessels afterwards coil in the midst of the fluid contents of the general cavity, that the former must absorb from the latter the elements from which the true blood is afterwards manufactured. It presents, in fact, according to our author, the same relation to the contents of the proper blood system of vessels as the chyle of the higher animals does to the true blood; the peritoneal fluid of the Annelida differing from the chyle of the mammalia only in the fact that the latter is contained in vessels, while the former rolls in a capacious chamber.

Although we are deeply indebted to M. Milne-Edwards for his ample exposition of the colour and distribution of the blood in the Annelida,¹ he appears to have overlooked, if not mistaken, its corpuscular or microscopic character. "Mais, du reste," he remarks, "examiné au microscope, ce liquide ne m'a pas semblé differer du sang des autres animaux sans vertèbres. Les globules qu'on y voit nager n'ont pas du tout l'aspect de ceux propres au sang des animaux vertébrés; ce sont des corpuscules circulaires, dont la surface a une apparence framboisée, et dont les dimensions varient extrêmement chez un même animal." Mr Wharton Jones has also figured and described these blood corpuscles as supposed to exist in the earth-worm and leech.² Now, Dr Williams, after the most careful and extended examination, states as follows:—

"In no single species among the Annelida does the blood proper contain any morphic element whatever! In all instances, without a single known exception, it is a perfectly amorphous fluid, presenting under the highest powers of the best microscope no visible corpuscles or molecules, or cells whatever; it is a limpid fluid variously coloured, as originally and correctly described by M. Milne-Edwards, in different species. No complete distinction into venous and arterial blood can be observed, and the plan of the circulation renders such a distinction only partially possible. In all cases the colouring matter is fluidified, and uniformly blended with the fluid mass of the blood; the colour therefore must be developed in the fluid mass, for there exist here no morphic elements in the blood itself by which the separation of the coloured substances from the peritoneal fluid can be effected, unless indeed the parietes of the vessels of the blood-proper discharge this eclectic function. With one exception, namely, that of Glycera alba, in which they are red, the corpuscles of the peritoneal fluid are in all species destitute of colour. But it is not at all chemically impossible that the coloured ingredients may exist in this fluid in a colourless state, and that these ingredients, through entering into new combinations, may become brightly coloured after transition into the true blood. In consequence of the impracticable minuteness of the quantity, no direct chemical analysis of the blood in the Annelida can be executed. As to the colour, however, analogy removes all doubt that the red tinge is due to the salts of iron, and the green to those of copper. In those species in which the blood is light, yellow, opaque, or lymph-like, it does not follow that the salts of the coloured minerals are altogether absent; they may exist under colourless combinations. The physiologist cannot view with unconcern the question, which in this class of animals affects the mode in which the peritoneal fluid and the blood-proper stand related to each other. That the former is higher than the latter in degree of organization, no doubt can exist; but it

is not quite clear that the true blood is reproduced out of the elements of the peritoneal fluid; since the vessels distributed over the parietes of the alimentary canal may take up some of the immediate products of digestion, before the latter exude into the general cavity of the body to mingle with its semi-aqueous contents. Nor can it be affirmed, from the evidence drawn from its composition, that the peritoneal fluid is unfitted to supply the means of nutrition to the solid structures, into the interior of which in every part of the body it intimately penetrates. It is more probable, because more in accordance with analogy, however, to suppose, that it is a manufactory in itself; that its corpuscles execute an office by which the mineral substances and proximate principles are vitally assimilated; that the corpuscular elements in the Annelida do in this fluid, what in the higher animals analogous bodies effect in the blood-proper. From these facts the physiologist may advisedly say thus much, that in these animals nature divides the vital fluids into two separate and distinct orders, on one of which the preparative and elaborative cell-agency devolves, on the other the work of solid nutrition. They prove with great clearness, that the corpuscular elements, either in the blood itself, or, as in this case, in some contributory fluid, are essential to the preparation of the blood-proper; for when in the zoological series, as in the higher articulata, this corpusculated fluid disappears, the blood itself becomes corpusculated; or when the peritoneal fluid, as in the Echinodermata, becomes less organic, then also morphic elements are developed in the true blood. From these observations the inference may be further drawn, that between these two nutritious fluids there exists a definite physiological balance; that one is capable of absorbing or merging into the other, according as the observer ascends or descends the organic scale. The peritoneal system of fluid terminates at the standard of the insect, the true blood system traced downwards terminates at the Echinodermata.³

The swelling of certain portions of the body in progression may be regarded as due to the interior fluids. These are driven to a given point of the containing cavity, where they are momentarily imprisoned by the contraction of the circular integumentary muscles before and behind,—thus producing a bulging. The muscles of the integument are then excited to action, and the fluid is forcibly compressed forwards or backwards, in accordance with the direction of the muscular agency. This is the mechanical use of the chyle-aqueous fluids of the peritoneal cavity, the physiological purposes of which have been already explained. Almost all the Annelida are struck, as it were, by paralysis, when this fluid is made to escape from its cavity by a puncture through the external walls. The power of motion is immediately suspended, and the body becomes flaccid and passive. The peritoneal fluid is really the fulcrum on which all muscular action is based, and without it these creatures cannot make the required contractions with sufficient effect and precision. But this is not the only mechanical use which it affords. It prevents that injurious pressure amid the internal organs which might impede or arrest the circulation of the blood. In the leech tribe it is the fluid contained within the stomach that accomplishes this important object. "Nothing in the history of the Annelida," says Dr Williams, "can be conceived more wonderful than the mechanically perfect and facile manner in which Linus longissimus, a worm of many yards in length, performs the feat of locomotion, and that too over craggy and rugged rocks." Without the conjoined action of these internal fluids, the motor apparatus would be incapable of effort.

The Annelida, as a class, may be said to undergo, in their earlier stages, few, if any, metamorphoses. The young

¹ Annales des Sciences, October 1838.

² Phil. Trans., Part II, 1846.

³ Report, p. 175.

Annelida. seem at first to be entirely devoid of appendages, but the body does not in any instance exhibit those peculiar transmutations so observable in the growth of insects and crustacea.

In regard to the external parts, we shall here indicate a few of the most important,—premising, that the characters mentioned are not universal to the class, but rather confined to certain races. The head, in such as possess one, is a small anterior swelling, which bears the antennæ commonly so called, and the eyes, and is distinct from the first segment of the body. The Nereids of Linnæus are regarded by Latreille as the only Annelida of which the anterior segment merits the name of head, or possesses organs fit to be compared to eyes, more especially to those of the larvæ of insects. The eyes, where such exist, are simple, extremely small, and appear like blackish points. The organization of the mouth varies greatly in the different orders. The parts called maxillæ by Savigny are hard circumscribed parts, of a corneous or calcareous nature, to which Latreille does not accord the name of jaws. The latter author indeed seems to regard the Annelida as a suctorial rather than a masticating class. Most of them are of carnivorous habits, and live on the blood of other creatures. The trunk or sucker is a contractile fleshy portion, constituting the mouth, and containing the so-called jaws. The latter portions, however, being adherent to the inner coats of the sucker, which is itself nothing more than a prolongation of the œsophagus, can scarcely be regarded as genuine jaws.

Several tribes have their branchiæ uniformly spread over the extent of the body, or over its central portion, while others (and these usually dwell in tubes) bear those organs at their anterior extremity. In the erratic species, or such as are naked, and without fixed dwellings, they are usually disposed longitudinally along the sides of the body, there being one for each foot. Blood-vessels sometimes appear to spread into the setiform processes, and to convert them into respiratory organs.

We have already stated that Linnæus placed the Annelida in his almost unlimited class of Vermes,—a vast and by no means well-combined group, which the later labours of Otho Frederick Müller, Pallas, and other naturalists, failed to cast into a much more natural mould. The great Swedish naturalist separated the true Annelida from each other, placing one portion of the group in the order Intestina, and the other in that of Mollusca. In Cuvier's earliest work (Tableau Élémentaire, &c., 1789), he restricted the class of worms to the Annelida and intestinal species, a mode of grouping previously practised by Bruguière in the Encyclopédie Méthodique. Subsequent investigations induced the French anatomist to raise the former to the rank of a separate class, which he named Vers à sans rouge, in a memoir read to the French Institute in 1802. On this same group Lamarck (Extrait du Cours, &c., 1812) bestowed the name of ANNELIDES,¹ which has since been very generally adopted. A slight disparity, however, still exists in the constitution of the class, in the works of Cuvier and Lamarck, the former including therein the genus Gordius, which the latter associates with the other Vermes.

But notwithstanding the valuable labours of these and

other writers, the external structure of the Annelida cannot be said to have been at all rigorously determined, or viewed in relation to that of conterminous groups, till we received the fruits of Savigny's laborious and most delicate observations, originally presented to the Academy of Sciences.² At that period Blainville was also occupied in the study of the same group, which, with the exception of the leeches, forms his class of Stipodes. He published an extract from his labours in the course of the ensuing year.³ Oken, Leach, Latreille, Dugès, Audouin, Milne-Edwards, and others, have likewise contributed to our knowledge of this curious and important class, in publications, to the majority of which we shall more particularly allude in the course of the present treatise.

In regard to the geographical distribution of the Annelida, our data are not yet sufficiently precise and numerous to admit of any satisfactory generalization. We have already said, that with the exception of the earth-worms (and even these require a moist abode), all the known species are aquatic. We may add, that the great majority inhabit the saline waters of the ocean. Most of the Naidæ, however, occur in fresh water, and some true Nereids are found in the lakes of North America. Annelida of some kind or other are met with in all quarters of the globe, and the species of many genera are very widely distributed; but others, such as the Amphinomeæ, for example, are characteristic of, if not peculiar to, the warmer seas. Undoubtedly the most magnificent are native to the Indian shores. It is in general on the coasts of the sea, in the midst of Thalassophytes, in the anfractuities of madrepores, in the sand, and particularly in mud, that the Chetopoda are to be found; and if some species are more commonly to be met with in the open sea, as, for instance, the Amphinomeæ, named by M. Savigny Pleione vagans, it appears that they may have been drawn along with marine plants by the currents, as is the case with many other animals.⁴ Their natural movements are extremely slow, and may be compared to those of slugs, although their appendages for locomotion are much more numerous. The Nereides, however, not only creep in a kind of serpentine manner over the surface of solid bodies at the water's edge, but frequently swim very respectably, either by successive undulations of the body, after the manner of eels and serpents, or by agitating their appendages, and thus making these organs serve as oars.⁵

The utility, in an economical point of view, of the Annelida in general, to the human race, is by no means great. According to Pallas, the inhabitants of some parts of Belgium eat those portions of Aphrodita aculeata which compose the mouth; the Nereides and Arenicolæ, as well as the earth-worms, are extensively employed as baits for fish, and the medicinal uses of the leech are notorious; but, with these, and, it may be, a few other exceptions, little can be said regarding the direct benefits derivable from this peculiar class. Its subjects, however, are by no means on that account the less important in the eyes of the philosophical naturalist.

Several of the Annelida possess a phosphoric property, from which Linnæus named a certain species Nereis noctiluca. Others, characterized by the same attribute, were afterwards described by Sig. Viviani.⁶

¹ From annelus, a little ring. The body of these animals is composed of a series of annuli or rings, a formation which suggested to Lamarck the general name which they now bear. The substance of these rings is neither horny nor calcareous, but soft and fleshy, and thus so far differs from the truly articulated tribes in the entire absence of any approach to a hard skeleton, or the consistent covering of insects. The segments are divided from each other only by a circular band of muscular fibres, the annulations not being perfectly distinct from each other,—the longitudinal muscles passing over and under the constricting circular bands. Thus, as Dr Williams remarks, these segmentations of the Annelida are more apparent than actual. In addition to the works mentioned in the course of this article we would especially recommend Dr Williams' Report already referred to, and of which we have made frequent use. We may moreover refer the reader to M. de Quatrefages' Études sur les types inférieurs de l'embranchement des Annelides, consisting of many Mémoires published in the Annales des Sciences Nat., 3^me série, for the years 1848, 1850, and 1852. See also Siebold's Anatomy of the Invertebrata (translated by Dr Burnett), London, 1854; Dr Carpenter's General Physiology, 5th edit., Ibid., 1854; and Mr Rymer Jones's General Structure of the Animal Kingdom, 2d ed., Ibid., 1855.

² Système des Annelides, forming a portion of the great French work on Egypt.

³ Bulletin de la Soc. Phil., Mai et Juin 1818.

⁴ Griffith's Animal Kingdom, vol. xiii., p. 73.

⁵ The lateral parts are hence named romæ by M. Savigny.

⁶ Phosphorenia maris quatuordecim luccescentium animalculorum novis speciebus illustrata. Genuæ, 1805.

Annelida. The presence or absence of the organs of motion, and the position of the branchiae, furnish natural characters of easy application, which modern zoologists have employed to signalize the primary groups. Lamarck divides the Annelida into three orders—les Apodes, les Antennes, and les Sédentaires; and in the system of Cuvier they likewise form an equal number of orders—les Tubicoles, les Dorsibranches, and les Abranches. In both systems the Serpula occupy the highest position in the scale. Savigny's arrangement of these animals consists of five orders, of which the author has as yet treated only of four—viz., les Néréidées, les Serpulées, les Lombricines, and les Hirudinées. He places the Aphrodites and Nereids at the head of the class. Latreille is also of opinion that these Annelida, especially the Nereides, so far as regards their external organization, are entitled to precedence, and make the nearest approach to the articulated animals provided with feet, such as Insects and Crustacea.

We shall here, in as far as general arrangement is concerned, follow the system of Cuvier.¹

ORDER I.—TUBICOLÆ, Cuv.

Some form a calcareous homogeneous tube, supposed to result from transudation, like the covering of testaceous Mollusca, but which does not adhere by any muscular attachment; others construct a covering by agglutinating grains of sand, broken shells, and other debris, by means of a membrane, likewise the result of transudation; while a third group are surrounded by a tube of an entirely membranous or corneous nature.

GENUS SERPULA, Linn. The body is composed of numerous segments; its anterior portion is enlarged in the form of a disk, armed on either side by several bundles of stiff bristles; and on each side of the mouth is a fan-shaped plume of branchiae, usually adorned by lively colours. At the base of each plume is a fleshy filament, one or other of which is always prolonged and dilated at the extremity into a disk of various form, which serves as an operculum, and closes the orifice of the tube whenever the contained creature chooses to retire. Of this genus the calcareous tubes cover, by their tortuous windings, the surface of stones, shells, and other submarine bodies. The species are widely distributed throughout the seas of Europe, India, and America. The largest are indigenous to the warmer climates of the globe. Little is known of their instinctive habits or natural economy. They are said to feed on aquatic animalcules, which they seize by means of their branchial tentacula.

Linnaeus, and most of the naturalists of his time, placed the Serpula among the testaceous Mollusca. They now constitute a numerous genus, of which several species occur

in the European seas. They are very contractile, and are supposed to feed on animalcules. A well-known species, S. contortuplicata (fig. 1), has rounded tortuous tubes, of about three lines in diameter. Its operculum is tunnel-shaped, and its branchiae are often of a beautiful red, or varied with yellow and violet. Any object thrown into the sea is apt to be speedily covered by this species.

In tropical seas they usually form their encrusting habitations in the midst of corals, lengthening their tubes as the coral is built up around them. Their extent is sometimes equal to three feet; and the expanded gill-tufts are of extremely vivid colours, equalling in brilliancy the brightest carnations. Some of the many small species which occur along our own coasts are also remarkable for the beautiful tinting of their gills.

GENUS SPIROBIS, Lam. Branchiae much less numerous than in the preceding genus (from three to four on each side), placed anteriorly in a somewhat radiated form. A pediculated operculum, with a flat summit placed between the branchiae. Tube testaceous, and rolled after the manner of a Cornu ammonis.

This genus is composed of very small species, which are found attached to fuci, shells, and other marine bodies. They frequently occur in great numbers, though always separate from each other. The animals are of a blood-red colour. We have figured the Sp. nautiloides of Lam. (fig. 2) synonymous with the Serpula spirorbis of Linn.

GENUS SABELLA, Cuv. Amphitrite, Lamarck. Body and fan-shaped branchiae resembling those of the preceding genus, but both the fleshy filaments adhering to branchiae terminate in a point, and do not form an operculum; they are sometimes even wanting. Their tube is rarely calcareous, and seems often formed of grains of very fine clay or mud. Most of the ascertained species are of considerable size, and are remarkable for the extreme delicacy and lustre of their plumed branchiae.

One of the most splendid of the genus is figured by Dr Shaw under the title of Tubularia magnifica.² It is found on various parts of the coast of Jamaica, adhering to the rocks. It is extremely wavy, and when approached instantly recedes within its tube, which on a further alarm also retires into the rock, so that specimens can be obtained only by breaking off portions of the mass. These, when put into tubs of sea-water, may be preserved for months, and the habits of the animals attentively studied. The species in question is characterized by a simple undulated tube of a whitish hue, the tentacula being varied by beautiful alternate bands of red and white. Sab. vesiculosa (fig. 3) is a British species described by Montagu.³ The internal texture of its tube is coriaceous, but the outer coat is invariably covered by coarse sand, intermixed with fragments of shells. Considerable variety exists in the form and aspect of the genus Sabella.

¹ Règne Animal (ed. 1830), vol. III. See also the two following works:—Symptotische Übersicht der Ringthwürmer oder Anneliden: Nach Cuvier's Classification. (Mit vielen Abbildgn.) Lithogr. gr. imp. fol., Ebend. 1841. Schmidt's Neue Beiträge zur Naturgeschichte der Würmer, Jena, 1848.

² Linn. Trans. v., p. 228, tab. 9.

³ Héd. xi., p. 19, tab. 5.

GENUS TEREBELLA, Cuv. These, like the preceding, inhabit a tube of their own formation, but composed of coarser materials than that of the generality of Sabellæ. Their body presents much fewer segments, and the head is otherwise adorned. Numerous filiform tentacula, capable of great extension, surround the mouth; and on the neck are placed the branchiæ, which are not fan-shaped, but in the form of little branches.

The animals of this genus, according to Montagu, either prepare a sheath from the tenacious secretion of their own bodies, mixed with adventitious matters, or reside in prepared perforations at the bottom of the sea. Their tubes are in general so extremely fragile as to be easily destroyed, and the animals are then found lurking beneath stones, or forming a new dwelling. Some fabricate their tube in old shells or stones, to which they adhere by their entire length, while others fix a tube perpendicularly in the sand. These tubes are indeed frequently observed to obtrude several inches above the surface of the soil, and when the waters flow, the gills and other appendages are stretched forth, and seem agitated to and fro. The gills or branchial appendages are extremely sensible, of a fine blood colour, and when touched they contract so suddenly as to expel the fluid which they contain, and then they lose their sanguine hue.

The cephalic tentacles form auxiliary organs of respiration, not for the aeration of the blood-proper, but for that of the peritoneal fluid already mentioned, by which they are filled. They exhibit some peculiar features. From their great length and vast number, they expose a large aggregate surface to the action of the surrounding medium. The lower surface of each tentacle is clothed with cilia, and is thinner than the dorsal aspect. The richly corpusculated peritoneal fluid enters freely into the hollow axis of all these tentacles, and is thus brought into contact with the surrounding waters. The tentacles themselves can grasp a grain of sand or other minute fragment, at any point of their length, or, if placed in a linear series, a row of grains. So perfect is the order of the muscular fibres at the extremity of each filament, that it is gifted with the twofold power of suction and ordinary muscular action. When the tentacle is about to seize upon an object, its extremity is drawn inwards (like a portion of the finger of a glove reversed) in consequence of the sudden reflex of the interior fluid. By this movement a cup-shaped cavity is formed, in which the object is securely held by atmospheric pressure—a power immediately reinforced by the contraction of the circular muscular fibres.

In addition to these important purposes, the tentacles of the Terebellæ are also the organs of locomotion. Being outstretched by the ejection into their interior of the peritoneal fluid—a process effected by an undulatory contraction of the body from behind forwards—they are next attached like so many slender cables to a comparatively distant surface, and being then shortened, the otherwise helpless body is hauled forwards. The concentration of the tentacles and branchiæ around the head in this genus, gives a great development in that quarter to the circulating system.

The generative apparatus conforms in its general arrangement with that of the earth-worm, and others, in presenting a segmental repetition of the ovigerous organs, while the male portion is grouped together in a lobated mass at the mesial line. We owe to M. Milne-Edwards a detailed account of the development of the young.¹ On first leaving the egg they exhibit no resemblance whatever to their parents, but might rather be mistaken for the ciliated larvae of Polypi or Medusæ, presenting no vestige of the annular

type of form. Ere long, however, their bodies become elongated, and begin to assume a somewhat symmetrical or two-sided form, consisting of four zones or rudimentary segments, the posterior of which is continuous, provided with a ciliary apparatus. A fifth ring next makes its appearance between the penultimate and terminal joint, while the rudiments of the mouth and alimentary canal become distinguishable. The growth now advances rapidly, the body becoming more worm-like as the segments are added between the last-formed segment and the terminal one. It is observable that the originally ultimate segment continues so to the end. Simple subulate setæ, supported by small fleshy tubercles, begin to appear on both sides, and the larva is no longer apodous. At this period it resembles a minute sub-cylindrical worm, and in a few days the cilia entirely disappear, the body now exhibiting the aspect of one of the erratic Annelids, in no respect resembling the tubicolous genus to which it actually belongs, and is ere long transformed into. This young larva is furnished with a distinct head, an antennary organ, eyes, and feet, provided with subulate setæ; while we afterwards come to know, that the adult or perfect state, as we are wont to term it, have neither head, eyes, nor antennæ, and exhibit feet furnished with hook-like appendages. Having lost its locomotive cilia, it now ceases to swim, and begins to inclose itself in a kind of mucous substance, which gradually solidifies into a cylindrical tube, open at both ends. The first stage of its existence, during which it has led an unfixed or erratic life, now closes, and it commences a life similar to that of its parents. The ventral oars, armed with terminal hooklets are successively developed, as are also the tentacular appendages around the head; but it is not till the creature has acquired some forty pair of feet, that the branchial apparatus begins to show itself under the form of two simple tubercles, springing from the lateral regions of the neck.

Dr Williams states that the number of setiferous feet constitutes by far the best character for the fixation of the boundaries of species. Between several of these, as constituted by Montagu, there is no actual difference but that of the age of the observed individuals. Many of the Terebellæ are gregarious, and some are so numerous that the sea-shore after a storm is seen to be covered with their fragments. When their tubes are entire, but a small portion of the body is protruded, with the exception of the long filiform tentacles, which are thrust about in all directions as if in search of food. The branchial appendages previously mentioned as so finely coloured during healthy life, are observed to lose their brightness from day to day as the animals become sickly in confinement.

Terebella gigantea, Mont., the largest of the genus, measures sixteen inches in length, and occurs, though rarely, on the coast of Devonshire.

GENUS AMPHITRITE, Cuv. Pectinaria, Lam. Recognizable by the golden-coloured bristles ranged in a coronal or pectinated manner, in one or more rows, on the anterior portion of the head, where they probably serve either as a means of defence, for the purposes of locomotion,² or for collecting the materials of their dwelling. Numerous tentacula surround the mouth, and at the commencement of the back, on either side, there are comb-shaped branchiæ.

The gills or branchial appendages of this genus are attached to the anterior part only of the body; and this is the case, in fact, with all the tribes that inhabit tubes, because gills attached to the other parts which are covered, would be useless for the purposes of respiration.³

¹ Recherches Anatomiques et Zoologiques faites pendant un Voyage sur les Côtes de la Sicile. Annales des Sciences Nat., 3^e série, Zool. t. III. (Mars 1845).

² Montagu observed Terebella venustula fixing its tentacula, and then, by contracting them, draw its body forward.

³ Griffith's Animal Kingdom, vol. xlii., p. 88.

Certain species construct very light and delicate tubes, in the form of a lengthened cone, which they carry along in the course of their travels. Their golden bristles form two combs, the teeth of which are directed downwards. Their intestine is very ample, folded several times, and is usually filled with sand. A well-known European species is the Amph. auricoma Belgica of Gmelin, of which we have given two representations (fig. 4). Its tube measures about two inches in length, and is formed of little rounded grains of various colours. Other species attach their tubes to different substances; and their golden setæ form upon the head several concentric crowns, from which an operculum is produced, which closes the tube when the animal is in a state of contraction. Each foot is furnished with a cirrhus, and the body, terminating posteriorly in a tube curved towards the head, is provided with a kind of muscular gizzard.¹ To these belong Amph. alveolata, Ellis, Corall. 37, of which the tubes, combined in a compact mass, present regularly disposed orifices, resembling the cells of a piece of honeycomb. Another species, Amph. ostreaaria of Cuvier, forms its tubes on the shells of oysters, and is said to be extremely injurious to the increase of that valuable mollusc.

Cuvier has placed in this order of Annelida the singular genus SYPHOSTOMA (fig. 6), first made known by Dr Otto in a dissertation published at Breslau in 1820. It appears to have two anterior openings or mouths.²

Here also, but with a very doubtful claim, the genus DENTALIUM (fig. 5) is allowed to stand. Its covering is a solid calcareous shell, in the form of an arched elongated cone, open at both ends, and compared by some to a small tusk of an elephant. The animal itself does not appear to be in any way articulated, nor to possess lateral setæ. Its body is of a conical form, like that of the shell, and is very smooth and compact.³

It seems now to be determined that the position of this last-named genus in the Cuvierian system was a misplacement. Dr Williams is very clearly of opinion that the researches of Deshayes and Savigny, and more satisfactorily of M. de Blainville and Mr Clark (in Annals of Nat. Hist. for Nov. 1849), have proved that the Dentaliæ are gasteropodous Mollusca, ranking somewhere be-

tween Chiton and Patella. In Dentalium, the symmetrical sub-ventral position of the branchiæ, the posterior flow of water which takes place in them, and the resemblance of the foot to that of some of the bivalves, appear in a striking manner to prove its connection with the Conchifera, whilst by its œsophageal cerebral ganglions, and the completeness of its circulating system, its affinity to the Gasteropod is established. But neither can it be disputed that the genus exhibits some peculiar approximations to the Annelida or annulose tribes; such as the red blood, the vermiform configuration of the posterior portion of the body, the tubular figure of the shell, the operation of the operculum, and the apparent resemblance of the branchiæ to those of the Sabellæ. All these characters may readily be viewed as prefiguring some of the outward features of the Annelida, although they are in truth only analogies of an apparent and superficial nature. The species have therefore been excluded from the latter class in Dr Williams' Report. Our author maintains the close and natural approximation of the Annelida and Entozoa.

The genera of this order bear their branchiæ throughout the length of their body, or are at least along its middle portion, and in the various forms of branches, tufts, plates, or tubercles, in which the sanguineous vessels ramify. The majority of the species live in the mud, or swim freely in the sea. A few dwell in tubes.⁴

Those in which the branchiæ are most highly developed are placed at the head of the order.

GENUS ARENICOLA, Lam. Branchiæ numerous, complicated, bush-shaped, and disposed over the intermediate segments of the body. Mouth terminal, in the form of a dilatable fleshy trunk, without either teeth or tentacula. No apparent eyes. The posterior extremity wants both the branchiæ and the bundles of setæ with which the other segments are furnished. There are no cirrhi to any part of the body.

This genus was established by Lamarck, at the expense of the old genus Lumbricus of Linnæus. The best-known species, A. piscatorum (Lum. marinus, Linn.) or lug-worm (fig. 7), measures about a foot in length, and bears thirteen pair of branchiæ. It is of a reddish colour, and, when handled, stains the fingers of a fine yellow. It inhabits moist sand by the sea-shore, and is much used as a bait by fishermen.

This Annelid lives almost entirely by the swallowing of sand, and its position is indicated by the numerous little coils so frequent on the sea-shore below high-water mark. The sand traverses the entire extent of the animal's body, yielding for digestion and assimilation whatever it may contain of an organic nature, the residuum being rejected in the form of sand-coils. Deglutition, with this species, can only be performed when the sand is saturated with water. If too dry, it cannot be swallowed; if too wet, it cannot be seized by the proboscis.

Though the lug-worm may seem to inhabit the loose

¹ These species form the genus Sabellaria of Lamarck, and Hermella of Savigny. No department of natural history is more darkened by a confused cloud of synonyms than that which treats of the Annelida. "Ces perpétuels changements des noms," says Cuvier, "finiront par rendre l'étude de la nomenclature beaucoup plus difficile que celle des faits." (Règne Animal, t. iii., p. 195.)

² See the article Siphostoma, in the Dic. des Sciences Nat.

³ See Savigny, Système des Annelides, p. 98; and Deshayes, Monographie du Genre Dentale, in Mém. de la Soc. d'Hist. Nat. de Paris, t. ii., p. 321. We may here note, that the genus Dentalium (now classed with the molluscous tribes) seems to have been equally abundant in ancient as in modern times,—many of its calcareous tubes being found in a fossil state.

⁴ Consult Orsted's Grønlands Annelata dorsibranchia, Kjøbenhavn, 1843; and by the same author, Beschreibung der Plattwürmer, ibid., 1844.

Annelida. moist sand, or to perforate it merely mechanically, it is well known to secure the sides of the passage from closing in by applying to them a glutinous cement, which unites the particles of sand into a kind of wall or coating. This covering does not adhere to the body, but forms a surrounding tube, within which the animal moves with perfect freedom, and which it leaves behind it as it progressively advances; so that the passage is kept pervious throughout its entire length by means of the lining, which may not inaptly be compared to the brickwork of the shaft of a mine or tunnel.¹

As allied to Arenicola, we may here name a singular Annelid, or sea-worm, called Palolo, of which specimens were some years ago presented to the British Museum by the Rev. J. B. Stair.² It is described by Mr J. E. Gray as characterized by—"a cylindrical body, separated into equal joints, each joint with a small tuft of three or four spicula on the middle of each side. Head—? Last joint ending in a couple of tentacles. Eggs globular." Most of the specimens examined were unfortunately much broken; and as none of the portions possessed a head, Mr Gray very properly did not describe it. He names the species Palolo viridis. It is of a green colour, with a row of round black spots down the middle of the dorsal (?) surface,—one spot on the middle of each joint. The following is Mr Stair's account of its habits and locality:—

"Palolo is the native name for a species of sea-worm which is found in some parts of Samoa (the Navigator Islands), in the South Pacific Ocean. They come regularly in the months of October and November, during portions of two days in each month, viz., the day before, and the day on which, the moon is in her last quarter. They appear in much greater numbers on the second than on the first day of their rising, and are only observed for two or three hours in the early part of each morning of their appearance. At the first dawn of day they may be felt by the hand swimming on the surface of the water; and as the day advances their numbers increase, so that by the time the sun has risen thousands may be observed in a very small space, sporting merrily during their short visit to the surface of the ocean. On the second day they appear at the same time, and in a similar manner, but in such countless myriads that the surface of the ocean is covered with them to a considerable extent. On each day, after sporting for an hour or two, they disappear until the next season, and not one is ever observed during the intervening time. Sometimes, when plentiful at one island in one month, scarcely any are observed the next; but they always appear with great regularity at the times mentioned, and these are the only times at which they are observed throughout the whole year. They are found only in certain parts of the islands, generally near the openings of the reefs on portions of the coast on which much fresh water is found; but that is not always the case.

"In size they may be compared to a very fine straw, and are of various colours and lengths, green, brown, white, and speckled, and in appearance and mode of swimming resemble very small snakes. They are exceedingly brittle, and if broken into many pieces, each piece swims off as though it were an entire worm. No particular direction appeared to be taken by them in swimming. I observed carefully to see whether they came from sea-ward or rose from the reef, and feel assured they came from the latter place. The

natives are exceedingly fond of them, and calculate with great exactness the time of their appearance, which is looked forward to with great interest. The worms are caught in small baskets, beautifully made; and when taken on shore are tied up in leaves in small bundles and baked. Great quantities are eaten undressed, but either dressed or undressed are esteemed a great delicacy. Such is the desire to eat palolo by all classes, that immediately the fishing parties reach the shore, messengers are despatched in all directions with large quantities to parts of the island on which none appear."³

GENUS AMPHINOME, Brug. A pair of branchiae on each segment of the body, and two bundles of setæ, and a pair of cirri to each foot. The sucker is destitute of maxillæ.

This genus was formed by Bruguière from Aphrodita of Pallas, and Terebella of Gmelin. Savigny divides it into three, viz.,—

1st, Gen. CILAZIA, containing such as have five tentacula to the head, and branchiae in the form of tri-pinnate leaves.

We have figured as an example a large and beautiful species, C. capillata (fig. 8), remarkable for its long and thick-set bundles of setæ of a brilliant yellow, and its purple branchiae. It inhabits the Indian Seas. 2d, Gen. PLEIONE, containing those species which, with the same number of tentacula, have tufted branchiae. 3d, Gen. EUPHOSINE, containing species characterized by bushy branchiae (fig. 9), of a complicated structure, and strongly developed. The head is furnished with only a single tentaculum. The known species inhabit the Red Sea.

GENUS EUNICE, Cuv.—Leodice, Sav. Branchiae in the form of plumes, but the mouth or trunk armed with three pair of corneous maxillæ of different forms. Each foot has two cirri and a tuft of setæ. The head bears five tentacula placed above the mouth, and two on the nape of the neck. Some of the species are furnished with a pair of eyes.

This genus contains a monstrous worm, Eun. gigantea, Cuv., the largest of all known Annelida. It measures from four to six feet in length, and its body consists of 448 segments. Its colour is ashy grey, with an opalescent reflection. It inhabits the Indian Seas. Montagu (in Linn. Trans., vol. xi., pl. 3) has figured and described a species, under the title of

¹ Maund's Treasury of Natural History, p. 35.

² Proceedings of the Zoological Society, March 9, 1847.

³ We owe a recent notice of this marine worm (misnamed a fish) to the Rev. William Harbutt, now officiating under the London Missionary Society. The following is an extract of a letter (addressed to Mr R. M. Smith of Edinburgh,) dated Samoa, 9th December 1854:—"I remember I promised to send you a few of the singular fish which annually visits our shores, and only on one morning in the year—the day in which the moon enters her last quarter in November. I should say two days, for on the first day the fish are just seen, few in number, and for a few minutes; on the second in great numbers. This year I had an argument with the people here. They calculated that the fish would appear on the 11th and be taken on the 12th; I, by the almanac, told them the days would be the 12th and 13th, and I proved correct. I was at the fishing, and a busy hour it was." The specimens transmitted to Mr Smith did not arrive in very good condition. Palolo seems to be, if not brittle, at least what mineralogists term "easily frangible."

Annulida. Nereis sanguinea, but which, from the author's description of the jaws, is no doubt referrible to the present genus, or rather to that subdivision of it called MARPIYSA by Savigny, and distinguished by the absence of nuchal tentacula. The body is long, slightly depressed beneath, and its segments exceed 270, about 40 of which, at the posterior extremity, were of a much paler colour than the others, and appeared to Montagu as if they had been lately reproduced. The rest of the body was of a fine bronze colour, resplendent with changeable prismatic tints. It is a large species, measuring fourteen or fifteen inches in length. Eun. tubicola (fig. 10) inhabits the North Sea, and is remarkable for dwelling constantly in a solid corneous transparent tube.

After the preceding genera of the dorsibranchial order, of which the branchiae are complicated, Cuvier places those of which the respiratory organs are reduced to simple laminae, or even to slight tubercles. In some species, indeed, the branchiae are represented by cirri alone.

Some exhibit an alliance to the genus Eunice, in the strength of their jaws, and the unequal number of their antennae. Such are the genera LYSIDICE and AGLAURA of Savigny.

GENUS NEREIS, Cuv.—Lycoris, Sav. Tentacula of even numbers, attached to the sides of the base of the head, and a little further onwards two others bi-articulate, with a pair of simple tentacula between them. A single pair of maxillae in the proboscis. Branchiae composed of small plates, in which a net-work of sanguineous vessels is disposed. Each foot is moreover provided with two tubercles, two bundles of setæ, and an upper and under cirrus.

"The Nereides," it is observed in Mr Griffith's Supplement, "most usually live in the excavations of littoral rocks, in the hollows of sponges, in certain aleyones, in univalve or bivalve shells, in madrepores, in the interstices of the radicles of Thalassophytes, under stones, and in general in all bodies which present fissures more or less profound. There are some which bury themselves in mud or sand, where they excavate a lodge proportional to the dimensions of their body, and sometimes they line this dwelling with a mucous matter issuing from their body, in sufficient abundance to construct a tube or sheath. From this they put forth a greater or less portion of their body, but rarely the posterior extremity, so that they may be able to re-enter on the slightest indication of danger. They all appear to feed upon animal substances, whether in the living state, or in a state of putrefaction more or less advanced. M. Bose, who has observed the manners of some species on the coasts of the United States, tells us positively that these animals feed upon polypi and small worms, on which they throw themselves, by darting out the anterior part of their body, which they have first contracted. Otho Fabricius tells us of some species of Spio, or Nereides with tubes, that they seize the planariae on which they feed, by means of their long tentacula."

The species of this genus have a linear-shaped body,

more or less convex above, and composed of numerous segments. The term Sea Scolopendra, sometimes applied to them, expresses not inaptly their usual form. The species represented (fig. 11) is Nereis munita. N. margaritacea of Leach is distinguished by its pearly body, terminated by two long setæ. Its head is tri-lobate, with eight tentacula. This species is common near the Bell Rock, and is subject to great variation of colour.

Near the preceding Nereids may be classed several genera of the same slender form, and with branchiae reduced to simple plates, or even to threads or tubercles. In some the maxillæ and tentacula are absent.¹

GENUS PHYLLODOCE, Sav. Tentacula on the side of the head, in equal numbers, with four or five smaller ones in advance. Eyes apparent. Trunk large, and provided with a circle of very short fleshy tubercles. No apparent jaws. Branchiae broad, and in the form of leaves, thin, flat, and veined. Body linear, with many segments.

Ph. laminosa, Sav., is almost cylindrical, and consists of from 325 to 338 segments. It is of a brown colour, with reflections of purple and violet. Though nearly a foot long, it measures only a line and a half in breadth. It inhabits the shores of Nice. The Nereis lamelligera atlantica of Pallas² is probably a Phyllodoce.

GENUS ALCIOPA, Aud. and Edw. Mouth and tentacula resembling those of the preceding genus, but the feet or organs of movement present, in addition to the tubercles which bear the setæ and foliaceous cirri (branchiae), two branchial tubercles, which occupy the upper and under margins.

GENUS SPIO, Fab. Body slender, with two very long tentacula resembling antennæ. Head furnished with eyes. Branchiae on each segment of the body, in the form of a simple filament.

The species of this genus occur chiefly in the North Sea. They are of small size, and dwell in membranous tubes. They continually agitate their long tentacula. We have figured as an example the S. crenaticornis of Montagu (fig. 12).³

The tube of this species is extremely tender, being composed of minute adventitious matter slightly agglutinated. It is usually attached to Sertularia. In general the feet or tentacula are alone displayed; these are kept in constant motion, and are turned about in all directions, although they are at the same time capable of instantaneous contraction.

GENUS SYLLIS, Sav. Tentacula of uneven number, and moniliform, in common with the superior cirri of the feet. The latter very simple, with a single tuft of setæ.

Some diversity seems to exist in this genus in regard to

¹ Consult Rathkè De Bopyro et Nereide, Riga, 1837.

² Not to be confounded with the genus so named by Ranzani (in Mem. di Storia Natur. dec. prima, pl. i., fig. 2-9), at a period posterior to the publication of Savigny's work.

³ Nov. Act. Petrop., t. ii., 233, tab. 5.

⁴ Linn. Trans. xi., tab. 14, fig. 6 (not 3, as in the author's references to his own figures).

Annelids. the presence or absence of the so-called jaws. The segments of the body are very numerous.

S. Monilaris, Sav. (fig. 13) inhabits the Red Sea. Its body is long (consisting of 341 segments), slightly depressed, insensibly narrowed towards the tail, which terminates in two slender moniliform threads.

GENUS GLYCERA, Sav. Recognizable by the form of the head, which bears the shape of a fleshy conical point, resembling a little horn, and of which the summit is divided into four scarcely perceptible tentacula. The maxillæ are alleged to vary as in the preceding genus.

Few of the species have been observed in a recent state. G. unicornis is supposed by some to be identical with the Nereis alba of Muller and Gmelin. Its native country is unknown. G. Meckelii of Audouin and Edwards occurs on the shores of France.¹

GENUS NEPHTYS, Cuv. The species of this genus are distinguished by a trunk resembling that of Phyllodoce, but they want the tentacula, and have on each foot two bundles of setæ, widely separated, with an intermediate cirrhus.

The only species admitted by Savigny is N. Hombergii, discovered by the gentleman whose name it bears, near Havre de Grace.

GENUS LOMBRINERA, Blainv. Tentacula wanting. The body, which is extremely elongated, bears on each segment merely a little forked tubercle, from which issues a small bundle of setæ.

To this genus are referrible, among other species, the Nereis ebranchiata of Pallas,² and the Lumbricus fragilis of Muller.³ The latter forms the doubtful genus Scoletoma of Blainville.

GENUS ARICIA, Sav. Teeth and tentacula wanting. Body elongated, with two rows of lamellar cirri on the back. Anterior feet furnished with dentated crests, which are absent from the other organs of movement.

GENUS HESTONE, Sav. Body short, thickish, composed of few segments, and these not very distinguishable. A very long cirrhus, probably performing the functions of branchiæ, occupies the upper part of each foot, which has also another beneath, and a tuft of setæ. The sucker is large, but unprovided with either teeth or tentacula.

The species, though few in number, seem pretty widely distributed. H. splendida, Sav.⁴ (fig. 14) occurs on the coasts of the Red Sea, and was found by Mathieu on the Isle of France. H. festiva greatly resembles the preceding, though of smaller size. It was discovered in the neighbourhood of Nice, by M. Risso.⁵

GENUS OPHELIA, Sav. Body thick and short, with the segments not very apparent, and the setæ scarcely visible. For two-thirds of its extent long cirri serve as branchiæ. The palate contains a toothed crest, and the lips are surrounded by tentacula, of which the two upper are larger than the others.

O. bicornis, Sav., discovered by Orbigny, seems the only species yet distinctly known.

GENUS CIRRHATULUS, Lam. A very long branchial filament, and two small tufts of setæ on each segment of the

body. These segments are very numerous and closely set, and there is an additional range of filaments on the posterior part of what may be called the neck. The head, but slightly apparent, has neither jaws nor tentacula.

To this genus Lamarck (under the name of C. borealis) refers the Lumbricus cirrhatus of Otho Fabricius.⁶ Cuvier considers the Terebella tentaculata of Montagu⁷ as likewise being a species of Cirrhatus.

The body of this marine Vermis is long and slender, and composed of more than 200 annulations, each of which is furnished with two fasciculi of very minute bristles. There are no eyes, and the branchiæ are obscure. From the sides of the segments issue very long, red, capillary, appendages, most numerous near the anterior end, the extreme point of which, however, is destitute of them, and becomes acuminated. The mouth is placed on the inferior face. The posterior end is likewise obtusely pointed. The length of this animal is eight or nine inches. The colour of the upper portion is olive green; of the under, dull orange. While in a state of nature, the filiform appendages of the sides are in continual motion, appearing like slender red worms, twisting themselves around the body in all directions. This curious species was taken from a piece of timber that had been perforated by Pholodes, and was destitute of any natural covering.⁸ Although Montagu placed it in the genus Terebella, he expressed his doubts as to the genus to which it really belonged.

Cirrhatus Lamarckii, so abundant between tide-marks on the coast of Swansea, is described by Dr Williams as subsisting almost entirely by swallowing clay. Its long branchial appendages are but slightly, if at all subservient to the seizing of food. The mouth is a small circular orifice, situated ventrally a short distance below the tapering snout in which it terminates, and is well adapted for the suction of semi-fluid food. The native colours of this marine worm are beautifully variegated; the brilliant yellow of the intestine, which begins near the head and continues to the tail, being relieved by the greenish hue of the back, and contrasting well with the vermilion thread which spangles every portion of the body. This creature is capable of throwing out from the general cutaneous surface a considerable quantity of viscid secretion, by which it is enabled to roll itself within an impenetrable coat of mail. The mechanical art of applying the surrounding substances to the body is accomplished by the thready appendages; and nothing can be more exquisite and admirable than the perfect, though very rapid manner in which these microscopic strings accomplish their protecting work. In its natural state, Cirrhatus does not seem so much to inhabit channels, as soft semi-fluid clay, in which it is found beneath stones, near the ebb-mark of the tide.

GENUS PALMYRA, Sav. Setæ of the upper tufts large, flattened, fan-shaped, and shining with the brilliancy of polished gold; under tufts small. Cirri and branchiæ not much developed. Body elongated, with two rather long, and three very short tentacula.

The only known species is P. aurifera, a native of the Isle of France, from whence it was sent to Paris by M. Mathieu.

GENUS APHRODITA, Linn. Distinguished by its two longitudinal ranges of broad membranous scales, which cover the back, and beneath which the branchiæ, in the form of little fleshy crests, are concealed.⁹

The form of these Annelides is usually flattish, and is shorter and broader than in most of the genera. The interior contains a very thick and muscular œsophagus, sus-

¹ Lattor. de la France, Annelides, pl. vi., fig. 1.

² Nov. Act. Petrop., t. ii., pl. vi., fig. 2.

³ Ouvrage d'Egypte, pl. iii., fig. 3.

⁴ Linn. Trans. ix., pl. vi., fig. 2.

⁵ Ibid., p. 110.

⁶ Zool. Dan., pl. xxii.

⁷ Eur. Merid., t. iv., p. 418.

⁸ Fauna Granlandica, p. 231, fig. 5.

⁹ In the opinion of some observers, the Aphrodita offer an exception to the characters of their class, in not being possessed of red blood, but Cuvier has stated his belief (Regne Animal, t. iii., p. 186, note) that that feature is distinguishable in Aph. squamata.

Annelida. ceptible of being in part protruded outwards, like a trunk or sucker; there is likewise an unequal intestine, furnished on each side with a great number of branched cæca, of which the extremities are attached between the bases of the tufts of setæ, which serve as locomotive organs. It is alleged that the sexes are separate in the Aphroditaæ, and that the females are oviparous. At certain periods the female is certainly found filled with egg-like substances, which swim in a circumambient liquid, and the male is said to abound with milt.

The ordinal term of dorsibranchiate scarcely applies to the majority of the species, so many of which present no branchial appendages either on the back or elsewhere. They are exceptional also in this respect, that their blood is colourless. Respiration is performed on a different principle from that which pervades the other annelids. The blood-system is in abeyance, while that of the chyle-aqueous is exaggerated, and this fluid of the peritoneal cavity is in this group the exclusive medium through which oxygen is absorbed.

Savigny has raised this genus to the rank of a family, containing three genera, viz., Palmyra, already noticed, Halithea, and Polynoe.

To the genus Halithea belongs a well-known British species, Aph. aculeata, Linn. It is of an oval form, six or seven inches in length, and nearly two inches broad. The scales of the back are covered, and in part concealed, by a substance resembling tow, which takes its growth from the sides. From these sides also spring groups of strong spines, which partially pierce through the tow-like substance, and bundles of softer and more flexuous bristles, which shine with the brilliancy of gold, or exhibit the various tints of the rainbow, scarcely yielding in beauty, as Cuvier has observed, either to the lustrous plumage of the humming-bird, or the sparkling of precious gems. Lower down is a tubercle, from which spines issue in three groups, and of three different sizes, and lastly, a fleshy cone. There are forty of these tubercles on each side; and between the first two there are a pair of small fleshy tentacula. There are fifteen pair of broad scales, sometimes pursed, upon the back, and fifteen small branchial crests on each side. This curious creature is known along our native shores by the name of sea-mouse. Two other species, Aph. sericea and loystrix, are referrible to the same genus.

It appears from Dr Williams' observations that the true aphrodite type of respiration occurs in Aphrodita aculeata. In this species, the actual uses of the "elytra," or dorsal scales, become apparent. Furnished with a peculiar apparatus of muscles, they exhibit periodical movements of elevation and depression. Overspread by a coating of felt, easily permeable by the water, the space beneath the scales, during their elevation, becomes filled with a large volume of filtered water, which, during the descent of the scales, is forcibly emitted at the posterior end of the body. It is important to remark that the current thus established leaves only the exterior of the dorsal region of the body. It nowhere enters the internal cavities, the latter being shut up by a membranous partition from that spacious exterior enclosure bounded above by the felt and the elytra. The peritoneal chamber is very spacious in this species, and is filled by a fluid which only in a slight degree contains organized particles. The complex and labyrinthic appendages of the stomach lie floating in this fluid, and in the chambers which divide the roots of the feet. From this relation of contact between the peritoneal fluid and the digestive cæca, which are always filled by a dark green chyle,

Dr Williams regards it as impossible to resist the conclusion that the contained fluid is really a reservoir wherein the oxygen of the external respiratory current already referred to, becomes accumulated. From the peritoneal fluid the aerating element extends in the direction of the cæca, and imparts to their contents a higher character of organization. These contents thus prepared by a sojourn in the cæca of the stomach, become the direct pabulum for replenishing the true blood which is distributed in vessels over the parietes of those chylous repositories.

Another subdivision of the Linnæan Aphroditaæ has none of the flax-like substance on the back—the tentacula are five in number—and the trunk encloses strong corneous mandibles (fig. 15). It is named Polynoe by Savigny, and contains most of the old species described by Linnæus, Pallas, Muller, and Otho Fabricius. The Aph. clava of Montagu¹ is a Polynoe. Several other generic groups have been recently formed by Audouin, Milne-Edwards, and others, from the genus Aphrodita.²

In Erichson's Archives (for January 1845), we have an interesting note on the development and metamorphoses of Polynoe cirrata. It is born under a larva form greatly resembling the young of a very dissimilar genus Terebella. The eggs are found in packets on the back of the mother, and are of a bluish colour. The larva, of an ovoid form, and greenish colour, bears in front of its ciliated cincture a cephalic lobe, terminated by a little bundle of cilia, and enclosing two blackish eye-shaped points. The mouth is transverse, and is placed behind the ciliated collar.

GENUS CILATOPTERUS, Cuv. Mouth with neither trunk nor sucker, provided above with a lip, to which are attached two or three small tentacula. Then follows a disk, furnished with nine pair of feet, followed by a couple of long silky bundles like wings. The lamelliform branchiæ are attached rather to the under than the upper portion, and prevail along the middle of the body.

There is only one species of this singular genus, Ch. pergamantæus, Cuv. which measures from eight to ten inches in length, and inhabits a tube formed of a substance resembling parchment. It occurs in the West Indian seas.³

ORDER III.—ABRANCHIA.

In this the third principal division of the Annelida there is no apparent external organ of respiration. Certain species, like the earth-worm, seem to respire over the entire surface; others, like the leech, by interior cavities. We perceive a circulating system of closed vessels, generally filled with red blood, and a nervous knotted cord, as among the preceding groups.⁴ Some are furnished with setæ, which aid the locomotion, while others are destitute of these parts; from whence arises a subdivision into two principal families.

FAMILY I.—ABRANCHIA SETIGERA.

These are furnished with setæ, and correspond to the two genera Lumbricus and Nais of Linn.

GENUS LUMBRICUS, Cuv. Body long, contractile, cylindrical, divided by wrinkles into a great number of apparent rings. Mouth without teeth, subterminal, bilabiate, the upper lip larger than the other, advanced. No eyes.

¹ Linn. Trans. ix., pl. vii., fig. 3.

² For descriptive notices (with figures) of several rare and otherwise interesting British Annelids, consult a series of papers published in the Magazine of Natural History (chiefly volumes 6th and 7th), by an excellent observer, the late Dr Johnston of Berwick.

³ See M. Ant. Dugès Sur l'Anat. et Phys. des Annel. Abranch. in Ann. des Sciences Nat. for September 1828.

⁴ See Régne Animal, t. iii., p. 207.

Annelida. This genus corresponds to Enterion of Savigny, and contains the earth-worms and other species. The setæ are rough and short, as if unguiculated. Each segment is provided with eight of these setæ, that is, four on each side, united in pairs, and forming, by their distribution on the body, eight longitudinal rows, of which four are lateral and four inferior. From six to nine of the segments, comprised between the 26th and the 37th, are swollen, and form towards the anterior and superior portion of the body a kind of cincture, especially perceptible during the breeding season. In the interior of these creatures we perceive a straight wrinkled intestine, unprovided with a cæcum, but receiving in its course several muscular fibres (proper to the rings of the body), which form an equal amount of small diaphragms. Some internal whitish glands towards the anterior of the body are regarded as connected with the generative system. The nervous cord consists of a series or infinity of very small ganglia, closely set together. The circulation of the blood among the Lumbrici is by no means difficult to detect. We may perceive arising from the intestinal canal, and from the inner surface of the outer envelope, an infinite number of small venous vessels, which interlace with a great assemblage of arterial ones. These veins unite in one common trunk, placed longitudinally beneath the belly, and from that trunk proceed five small canals, which unite in a single dorsal vessel, which may be regarded as the heart. From the last-mentioned organ small arteries take their origin, and proceed to form a network with the veins of the superficies of the body,—thus completing the circulation. Respiration appears to be carried on at the surface of the skin, most likely by means of extremely small internal branchiae.

Annelida. many different kinds. Savigny, to whom we owe so much in relation to the Annelida in general, has, since the publication of his great work on that class, devoted his attention more particularly to the genus Lumbricus, and has ascertained the existence of about twenty-two species in the environs of Paris alone.¹

Earth-worms undoubtedly possess a certain reproductive power, when deprived of portions of their bodies, but not to the extent of producing perfect individuals from separated portions. It is easy to conceive that the removal of the hinder part of the body, which does not contain any organs essential to life, would not destroy the anterior portion; but that the hinder half, when left to itself, should reproduce the mouth, gizzard, stomach, and other important parts, was much less likely. On cutting an earth-worm into two, the anterior portion, according to Mr Rymer Jones, is generally found to survive; but this is not the case with the other end, which, although it may show signs of vitality for a length of time, possesses no power of reproduction, and eventually dies. The experiments, however, of M. Dugès, certainly go to prove that very important portions may be removed and reproduced. He cut off from four to eight of the anterior rings, thereby, of course, removing the cephalic pair of ganglia, the mouth, and a part of the œsophagus. After the lapse of from ten to thirty days, a conical vascular protuberance was perceived to sprout from the bottom of the wound; and in eight or ten days more, this new portion had become so far developed, that not only were all the removed rings apparent, but even the mouth and upper lip had assumed their pristine form, and the creature began to swallow food, and bury itself beneath the earth. Dr Williams' experiments, again, were attended by an entirely different result. He found that although the anterior half, after the bissection, did not lose the power of locomotion, its movements after a few days became much less active and vigorous. The wounded segment soon began to contract and wither away; and this process of dissolution, creeping onwards from segment to segment, the cephalic extremity, or head itself, soon ceased to live. The tail half loses at once all power of onward motion, and merely writhes about on one spot. Its movements become excited, not voluntary, and it never re-acquires the power of swallowing earth. The process of decay begins much sooner than in the other half, and, extending towards the tail, implicates first one ring, and then another, till the whole is dead.²

The common earth-worm, though apt to be despised and trodden on, is really a useful creature in its way. Mr Knapp describes it as the natural manurer of the soil, consuming on the surface the softer parts of decayed vegetable matters, and conveying downwards the more woody fibres, which there moulder and fertilize. They perforate the earth in all directions, thus rendering it permeable by air and water, both indispensable to vegetable life. According to Mr Darwin's mode of expression, they give a kind of undertillage to the land, performing the same below ground that the spade does above for the garden, and the plough for arable soil. It is, in consequence, chiefly of the natural operations of worms that fields which have been overspread with lime, burnt marl, or cinders, become in process of time covered by a finely divided soil, fitted for the support of vegetation. This result, though usually attributed by farmers to the "working down" of these materials, is really

The appearance of the common earth-worm (Lumbricus terrestris) is too familiar to need description in this place. We shall merely mention, that beneath the sixteenth segment there are two pores, the uses of which are still unknown. The mode of production is likewise still disputed. M. Montegre³ maintains that the eggs descend between the intestine and the outer envelope, around the rectum, where they hatch, and are speedily protruded in the living state. M. Dufour, on the contrary,⁴ asserts that they lay eggs resembling those of leeches⁵ (fig. 16). The ordinary habits of the earth-worm are well known. They inhabit moist earth, which they pierce in all directions, and a quantity of which they swallow. They also, however, feed on animal and vegetable remains, and always prefer soil imbued with those substances. They seek each other's society chiefly during the night, and in the month of June. Under the specific name of terrestris, naturalists have no doubt confounded

¹ Mém. du Mus., t. I., p. 242.

² Ann. des Sciences Nat., t. V., p. 17; and xiv., p. 216.

³ This seeming contrariety may be reconciled by bearing in mind that these creatures are in fact ovo-viviparous, and are sometimes born in the completed state, sometimes still surrounded by an envelope or egg-like covering. Dr Williams, however, has recently testified to the fact, from experimental observation, that the young escape from the ova before they leave the body of the parent, and are endowed with independent powers of locomotion.

⁴ See also M. Morren's Treatise De Lumbrici terrestris Historia Naturali nec non anatomica. Brux., 1829.

⁵ Hoffmeister has published some valuable researches regarding the various species of earth-worm, in his work, De vermiculis quibusdam ad genus Lumbricorum pertinentibus, Berol., 1842. To the genus Lumbricus, properly so called, he assigns six species, viz., Lumb. agricola, rubellus, anatomicus, riparius, oldus, and agilis, all of which occur in North Germany.

Annelida. due to the action of earthworms, as may be seen in the innumerable casts of which the initial soil consists. These are obviously produced by the digestive proceedings of the worms, which take into their intestinal canal a large quantity of the soil in which they feed and burrow, and then reject it in the form of the so-called casts. "In this manner," says Mr Darwin, "a field, manured with marl, has been covered, in the course of 80 years, with a bed of earth averaging 13 inches in thickness."

In the genus Hypogaon of Savigny, each segment is furnished with an additional seta on its dorsal surface, and the setæ are long, spiny, and sharp-pointed. The body in form and colour greatly resembles that of the common earthworm, but the segments are less numerous, not exceeding 106, whereas those of the latter amount to 120 and upwards. The only species with which we are acquainted is Hyp. hirtum, first observed in the neighbourhood of Philadelphia.

GENUS NAIS, LINN. Body elongated, linear, flattened, transparent or semi-transparent, and in general provided with lateral cilia, simple or in tufts. Segments less distinctly marked than in the earth-worm.

The synonymy of this genus is very confused, its nature and attributes obscure, and its position in the system consequently various, according to the views of different observers. The name, borrowed from the heathen mythology, was first applied by Muller, and was generally adopted by contemporaries, as it has been by succeeding, naturalists. It was written Naias by Bruguière (in Encyc. Méthod.), an erroneous alteration, in so far as the latter term had been previously consecrated by Linnaeus to a genus in botany. Lamouroux increased the confusion by bestowing the name of Naisa on a polypus genus of the family of Tubularia, already known by the title of Plumastella; and the resemblance of the two names has induced some compilers to refer to them as synonymous, although they in fact signify objects belonging to separate classes of the animal kingdom.

Lamarck and Cuvier, in preserving the name of Nais to the subjects of our present notice, do not agree regarding their relations to other groups. The former author places them in the third or concluding order of his class Vermes (Vers hispides), thus disposing them between the genus Gordius and the Epizoa. His reason for so doing is, that the structure of the Naidæ is by no means sufficiently composite to entitle them to a place among the true Annelida; and the fact of their being capable of multiplication by incision, shows that their nature is somewhat anomalous in relation to the last-named class. We may bear in mind, however, that notwithstanding the observations of Trembley and Roesel, their tomiparous generation is doubted by Bose, and denied by Dr Williams; and, all things considered, they may be regarded as more nearly related to the genera Nereis and Lumbricus than to any other.

The Naidæ in general are small vermiform creatures, of a few lines in length, of a reddish colour, though diaphanous, extremely active in their movements, and of a voracious disposition. They abound in fresh waters, where some dwell upon aquatic plants, others beneath stones, or in perforations in the mud. They prey on minute Crustacea, such as the genus Daphnia, and on the still smaller animalcula tribes, and are themselves greedily devoured by the fresh-water polypi, which swallow them up, notwithstanding the pointed cilia with which their sides are armed.

These cilia, however, and other apparently indigestible portions, are afterwards disgorged by the polypi, in the same manner as owls and other birds of prey reject from their stomachs little rounded pellets of hair and feathers.

The productive powers of the Naidæ, by whatever process accomplished, are truly astonishing. They appear in countless thousands in the waters of marshes after the lapse of a few hours, prior to which only some solitary individuals were perceptible. The mouth in these animals is sometimes a simple cleft, sometimes an opening, accompanied by two lips. The N. proboscidea of Gmelin, being provided with a trunk, forms the genus Stylaria of Lamarck; while certain anomalous species, such as Lumbricus tubifex and marinus of Muller, constitute the conterminous genus Tubifex of the former author. They dwell in perforations in the mud of streams and marshes, and in the sand of the sea-shore. We may conclude by observing, that the nervous system of the Naidæ is but obscurely known, and that the ocular points on the heads of certain species, though vaguely named eyes, cannot with actual certainty be regarded as organs of vision.

GENUS CLIMENA, LAM. Head without tentacula or other appendages. Body cylindrical, composed of few segments, somewhat swollen about the middle, and attenuated at either end. The posterior extremity is truncated and radiated.

These creatures inhabit fixed tubes of a cylindrical form and membranous texture, open at both ends. Our illustra-

Fig. 17.

tion represents Cl. amphistoma (fig. 17), a species taken in the Gulf of Suez, and indigenous to the shores of the Red Sea. Its tube is composed exteriorly of grains of sand and fragments of shells, and is usually attached to the interstices of rocks, or to Madreporites and other productions of the sea.

FAMILY II.—ABRANCHIA ASETIGERA.

This family comprehends such of the abbranchial order as are unprovided with setæ, and is constituted by the old genera Gordius and Hirudo of Linn., of which all the distinctly-known species are aquatic.¹ Dr Williams is of opinion that although all the Annelida may be comprised in the twofold division of branchiata and abbranchiata, such distribution would be neither convenient nor unobjectionable. Several species exist, such as those of the genus Syllis, in which the soft pedal appendages do not contain any specially organized branchial element. But the proposition is anatomically true, that the Annelida are really divisible into such as have and such as have not external and apparent branchial organs. The bipartite arrangement, long since propounded by M. Dumeril, of Crypto-branchia and Gymno-branchia, proceeded on this conception; the former term, however, being inaccurate, in so far as there is actually no species in which the branchiæ are internal or concealed. Respiration, according to Dr Williams, in all those destitute of external appendages, is performed internally, but not by any specially constructed organs. The function, under such circumstances, devolves either upon the general walls of the alimentary canal or external surface of the body, or

¹ We do not exactly know what species of the lower tribes is alluded to by Sir T. S. Raffles in one of his letters descriptive of an excursion from Benoolen. "I must not omit to tell you, that in passing through the forest, we were, much to our inconvenience, greatly annoyed by leeches; they got into our boots and shoes, which became filled with blood. At night, too, they fell off the leaves that sheltered us from the weather, and on awaking in the morning we found ourselves bleeding profusely. These were a species of intruders we were not prepared for." Another species of land leech is said to inhabit Madagascar, where it occurs on plants. It seizes greedily on the legs of the passers by, and sucks their blood.

Annelida. it is enacted by the fluid which, in nearly all the abbranchiate genera (except the leech and earth-worm), occupies the peritoneal cavity. All the external branchial appendages may be sub-divided into two chief divisions. In one, the organ is constructed with special reference to the exposure of the blood-proper to the agency of the respiratory element; in the other, the branchia is a mere hollow process filled with the chyle-aqueous fluid of the cavity just named.

It has been affirmed, as a law of the organization in all abbranchiate Annelida, that the system of the blood-proper is more developed on the parietes of the intestinal canal than on the integuments. This fact, whenever the peritoneal space is obliterated by the adherence of the intestinal cylinder to that of the integument, transfers the office of respiration from the latter to the former region; that is, as is practically demonstrable in the instance of Nais filiformis, the large volume of water which is incessantly streaming throughout the length of the alimentary canal, holding atmospheric air in solution, while it ministers by its organic particles to the nutrition of the system, contributes also by the air with which it is mixed to the great purpose of aerating the living fluids of the organism.

We may now observe that leeches in general (HIRUDINES) are characterized by an oblong body, sometimes depressed, transversely wrinkled, and furnished with a dilatable cavity at either extremity—that is, the mouth is surrounded by a lip, and the posterior end is provided with a flattened disk. These latter parts are useful as organs of prehension and locomotion, and also act as suckers. The mouth, placed in the anterior cavity, is furnished with three jaws.

These useful vermes were probably known in very ancient times. The Halukah or Gnalkah of the Hebrews appears to have been one of this tribe, at least the term has been so translated in our versions of the Proverbs, ch. xxx., v. 15: "The horse-leech hath two daughters, crying, Give, give." The Greek writers make mention of them under the name of Bdella, and the Latin authors under those of Hirudo and Sanguisuga; but the ascertainment of the precise species indicated is by no means easy. After the revival of learning we have various general notices of their history and habits, although it was so late as the time of Linnaeus before we attained to any knowledge of their specific distinctions. The Swedish naturalist (in his Fauna Suecica) described eight species, and numerous additions have been made in more recent times. For a long period the genus Hirudo, as founded by Ray and adopted by Linnaeus, experienced no sub-division; but the labours of Leach, Oken, Savigny, Lamarck, and others, have shown the propriety of re-arranging a group, consisting no doubt of natural constituent parts, but composed of beings exhibiting a varied range of structure, and too much extended for the formation of a genus, properly so called.

The structure of these creatures is soft and contractile, composed of a great number of articulations, and generally invested by an abundant supply of mucous moisture. The anterior cavity, which contains the mouth, is named capula by Savigny, while the posterior disk bears the name of cotyla in the nomenclature of that author. On the anterior segments certain small black points are observable, which are regarded as fulfilling the functions of eyes. They vary in number in the different genera, from two to ten. Various experiments have been made with a view to the ascertainment of their sense of sight. If we place leeches in a vessel surrounded by black paper, and permit the light to enter only by means of a single small orifice, they are by no means slow in directing themselves to that point;—but this observation we deem to be in no way conclusive, in as far as light produces an efficient action and a directing influence, not only upon many of the lowest tribes, which

we know to be destitute of eyes, but even upon the subjects of the vegetable kingdom. M. Moquin-Tandon however asserts, that having placed a small piece of red-coloured wood in front of Nephtelis vulgaris, it evidently turned round on purpose to avoid it.¹ Their perception of the sense of touch is delicate, although they possess no special or circumscribed organs for its reception. The sense of taste is obvious,—that of hearing and of smell imperceptible. No odour affects them,—no sound seems to produce any influence; nor can we detect any organs which may reasonably be deemed the seat of these last-named functions.

The tegumentary system of leeches has been examined in detail in very few species. In the medicinal leech three parts are, however, distinguishable—the epidermis, an intermediate layer which is the seat of colour, and the dermis. The epidermis is extremely fine and delicate, perfectly colourless, and remarkably deciduous, that is to say, it is frequently renewed, even as often as once in every four or five days in warm weather. It adheres intimately to the lower layer, but not by its entire extent—being frequently free between the rings of which the body of the creature is composed. When detached we perceive that it is perfectly transparent at the points which adhered to the coloured layer, and slightly opaque, or even of a whitish colour where it became unattached in passing from one segment to another. Under the microscope it is seen to be pierced by an infinity of small holes, through which a mucous liquid flows, which lubricates the surface. The coloured layer, or pigmentum, adheres strongly to the dermis on which it lies. The hues which it exhibits are very different according to the species,—sometimes they are dark and uniform, but usually lighter on the under than the upper surface; sometimes the ground colour is varied by spots or streaks of different intensities, while the pigment, if we may so express it, is occasionally almost colourless, and we may then perceive distinctly through the skin all the interior organs of the body. The dermis, or deepest layer, exhibits a curious organization; it consists of a thickish tunic, presenting an appearance of distinct circular articulations, which produce the ringed or wrinkled aspect of the external surface. The spaces which exist between these rings are covered by the epidermis, and seem intended to facilitate the varied movements of the animal.

Beneath the skin, of course, are placed the muscles. We find first a layer of transverse fibres, which adheres intimately to the dermis. This layer covers other muscles, of which the direction is longitudinal; and beneath these we find some more, of which the direction is again transverse.

The capula or oral sucker is formed by two extensible lips—the one superior, usually large, sometimes almost lanceolate; the other inferior, and less advanced. Within it are placed the jaws, rarely wanting, and usually three in number, disposed triangularly, and fixed upon a corresponding number of little tubercles. Their consistence is slightly cartilaginous, their form almost lenticular, and their margin, free and cutting, is sometimes smooth, sometimes furnished with a double row of dentations, more or less numerous according to the different kinds. A sort of cartilaginous ring, which frequently surrounds the base of the tubercles, indicates the opening of the intestinal canal, which commences by a species of oesophagus more or less narrow, presenting occasionally some longitudinal folds, but never any lateral pouch-like swellings. The ensuing portion or stomach, on the contrary, usually exhibits throughout its entire extent expansions more or less perceptible, according to the state of repletion. In certain species (such as Clepsina complanata) these lateral appendages are never effaced, but constitute permanent caeca. The rectum is generally

¹ Monographie de la famille des Hirudinées. Montpellier, 1826, in 4to.

Annelida. separated from the stomach by a valvular contraction. The anal opening is on the back, at the origin of the posterior sucker, called cotyla by Savigny. The digestive canal is throughout composed of two pellucid tunics, and towards its extremity some muscular fibres are perceptible. Although the existence of a liver in the leech tribe is not so ascertained as to be at all generally admitted (indeed it is denied by some, and doubted by many), yet M. Blainville describes an apparatus for the secretion of bile, consisting of a cellular-membranous tissue surrounding a portion of the stomach and intestine.¹

All leeches are blood-thirsty and voracious, and support themselves by sucking the life-blood of other animals. Their powers of digestion and assimilation are, however, extremely slow; and hence, probably their reluctance to repeat their operations for behoof of a patient, when their doing so is neither pleasant nor profitable to themselves. After the lapse of days, weeks, and even months, portions of the liquid or solid matters which they may have swallowed are found to remain in the intestinal canal. The kinds used in medicine, moreover, offer this peculiarity, that the blood which they have sucked does not seem to experience any sensible alteration in their stomach, but maintains its natural colour and fluidity. If, however, the leech dies, or the blood is exposed to the air, it speedily coagulates, and becomes of a blackish brown.

In regard to the bleeding of leeches, M. Olivier (Journal de Chirurgie par Malgaigne, 1844, Mars., p. 88), has proposed the following procedure:—When fully gorged, the creature should be punctured with the point of a lancet in one of the transverse wrinkles of the back, at the termination of the first third of the length of the body, the incision being made parallel with it, between the vein and artery, and in a direction from the anterior backwards. The wound is to be two millimetres in length, and the leech is to be afterwards placed in lukewarm water; in which, by its own contractions, which may be assisted by pressure with the fingers, all the blood which it has sucked escapes through the wound. It should afterwards be placed in rain or river water. It is said that, notwithstanding the carnivorous nature of these creatures, they are benefited by having access to the plant called Ranunculus aquaticus. The young are alleged to feed upon its leaves. On contemplating the singular dental apparatus of the leech, and considering the nature of the food (we presume minute aquatic animals) on which it usually subsists, Mr Rymer Jones finds it difficult to avoid the conclusion that such a structure is rather a provision subservient to the alleviation of human suffering, than necessary to supply the wants of the animals themselves. It is certain that in the streams, ponds, and marshes where they usually inhabit, an opportunity of sucking any warm-blooded animal, whether man or beast, must be extremely rare, so that they can but seldom exercise their instinctive love of blood. Neither does it appear that the fluid which they swallow so greedily is fitted to their constitution; for, although it is true that it remains for a considerable time in their interior without corrupting, yet it is well known that the death of the leech is generally caused by the indulgence of such inordinate repletion, provided the greater portion of what has been swallowed is not speedily regurgitated through the mouth.

The nervous system of the leech tribe has been described in some detail by several authors, especially that of San-guisuga officinalis, Hæmopis vorax, Nephtelis gigas, and Albione muricata. It is composed of a series of ganglions,

extending from the mouth to the extremity of the body, and placed, as among the other articulated classes, beneath the alimentary canal. From each ganglion proceed nervous threads, which ramify ad infinitum to the other parts.

Annelida. The circulating system of leeches has been the subject of still more numerous researches. It is probably more highly developed among these animals than in any other Annelida. In this class the presence or absence of a heart, or heart-like centre, is by no means the true criterion of its amount of evolution. The quantity of blood relatively to the size of the body, the degree of capillary subdivision on the periphery of the blood system, and the proportion of the latter to the peritoneal fluid, give true indications. In the leech there exists no free space between the intestine and the integument, and so the chylous fluid, which in nearly all the other Annelida occupies the general cavity of the body, is transferred into the interior of the lateral diverticula of the stomach. We shall here briefly notice the labours of some foreign physiologists. MM. Thomas,² Cuvier, Carena,³ Moquin-Tandon, Dugés⁴ and Audouin,⁵ have signalized themselves in this laborious field. All the species hitherto examined have presented four longitudinal vascular trunks—one dorsal, another ventral (these two being separated by the alimentary canal), and two lateral. These principal organs communicate with each other, not only by the capillary vessels which meet and intermingle in the different parts to which they are distributed, but also by special branches of considerable diameter, which proceed directly from one vascular trunk to another. The ventral vessel furnishes large branches, which, mounting vertically on either side, embrace the intestinal canal, and open on the dorsal vessel. Dugés names these the abdomino-dorsal branches. The lateral branches communicate with each other by means of transverse branches, which pass beneath the medullary cord. These branches have been well figured and described by Jean Muller (in Archiv. fur Anat. und Phys. Jan., März, 1828), and Dugés names them latero-abdominal branches. Lastly, these lateral trunks also send large branches to the dorsal vessel, which bear the designation of latero-dorsal branches. In addition to these canals, which thus establish a direct connection between the principal trunks, each of the latter gives rise to an infinite number of small vessels, which carry the blood to the various parts, and especially to the skin, which may be regarded as the principal, though not the sole organ of respiration. That other organ, to which we now allude, consists of certain pouches, amply provided with blood-vessels, which form a net-work on their coats, and proceed from the subdivision of a vessel furnished by the latero-abdominal branches, as well as of a large vascular pouch or bag called pulmonary by Dugés, and which is derived from the lateral trunk. In a species of Albione dissected by M. Audouin, the lateral vessels were perceived to be in direct communication with the respiratory pouches by means of two branches, one of which is anterior, the other posterior. He also observed that numerous branches sprang from the anterior portion of the dorsal vessel, and proceeded partly to the pouches, and partly to the lateral trunks. Thus the pouches communicate at the same time, both with the dorsal and lateral vessels. In accordance with these views, the process of circulation is supposed to be as follows:—The lateral trunks are regarded as great veins, which receive the blood from all parts of the body, and transmit it to the respiratory pouches, in which it becomes re-oxygenated; a small portion then flows back to the lateral vessels, while the greater portion

¹ Essai d'une Monographie de la famille des Hirudinées. Paris, 1827, in 8vo.

² Mém. pour servir à l'Histoire Nat. des Sangsues. Paris, 1806.

³ Monographie du Genre Hirudo, in Mém. de l'Acad. de Turin, tom. xxv.

⁴ Recherches sur la Circulation, &c., des Annelida Abranches, 1828.

⁵ Articles Sangsue and Sangsues, in the Dictionnaire Classique d'Hist. Nat.

Annelida. enters the dorsal vessel, and then the ventral one, both of which assist in propelling it to all the other parts of the body, from whence it returns to the lateral branches, and thence flows to the respiratory pouches as aforesaid. We must add, however, that M. de Blainville and others deny that the pouches or vesicular sacs just mentioned are of a pulmonary nature.¹ They regard them rather as secreting glands; and it is certain that respiration is carried on in great part through the medium of the skin, or rather that the function of breathing falls on the united structure of the intestine and integument. Various kinds of leeches may be often seen fixed by their posterior sucker, and swinging themselves to and fro for hours and even days together, their bodies being at that time more than usually flattened in order to render the motion more effective. They are then respiring after the manner of the Naid, by bringing their cutaneous system into constant contact with a fresh supply of water. During this singular process the pulmonary pouches are almost quite inert, and their sanguineous vessels scarcely perceptible, while the cutaneous network, on the contrary, is in full and remarkable activity.

Leeches are hermaphrodites, like others of their class; but sexual union of separate individuals is indispensable to the process of fecundation. Although in many of their more obvious characters they so nearly resemble the Planariae, they stand too high in the scale to be capable of reproduction by excision or the cutting of parts. A variety of opinion exists among naturalists regarding the mode of production, whether by eggs or living young. It is probable that such as do not appear to lay eggs are merely ovo-viviparous, and bring forth their young alive, after they have been hatched in the body of the parent. The majority of species in truth lay oviferous capsules, each containing several germs. Certain kinds of Clepsina are distinguished by a small and peculiar pouch in the abdomen, in which the young seek protection during infancy. They attain to full size rather slowly, and the duration of life is considerable, though not distinctly known. Medicinal leeches have been kept in life for a period of eight years; and it has been inferred that if, with the disadvantages of confinement and irregular supplies of food, they survive so long, their natural term of life must be much greater. This, however, we regard as an inconclusive, if not erroneous mode of reasoning; for we know that among insects and other classes of the more lowly organized departments of animal life, abstinence, and the non-fulfilment of their natural instincts, are uniformly found to prolong their period of existence.

The leech tribe in general is widely distributed over the earth's surface, although, as usual, each species has its own range of localities.² Our medicinal kinds seem proper to Europe, although they extend from Russia to the southern point of Spain. All the species are extremely sensible of atmospheric changes. They become agitated

during high winds, and often bury themselves in the mud during cloudy weather. Some fanciful observers have even kept them in confinement, that they might serve to indicate the state of the atmosphere; but we incline to think that it is fully as useful, and not more troublesome, to look out of a window than into a phial. On the approach of cold weather they sink into the mud, and pass the winter in a state of lethargy.

We shall now proceed to a brief consideration of the principal genera into which the tribe has been partitioned by modern naturalists.

GENUS SANGUISUGA, Sav. Oral sucker consisting of several segments. Upper lip almost lanceolate. Aperture transversal. Jaws three in number, compressed, and each armed on their cutting edges with two ranges of fine teeth. Eight or ten black points (regarded as eyes) disposed in a curved line; the posterior four more isolate.³ Anal sucker obliquely terminal.

This genus contains the leeches properly so called, that is, the medicinal kinds; and, according to Savigny, consists of three species. Some recent additions, however, have been made to these by MM. Moquin-Tandon and Carena.

H. medicinalis (fig. 18) of naturalists is the most common kind, and that most frequently used for blood-letting purposes. It occurs throughout the fresh-water marshes of Europe, and measures from four to five inches in what may be called its medium state, although capable of both contraction and extension within and beyond those limits. Its body, including the anterior sucker, is composed of ninety-eight rings, and is of a deep-green colour on the back, with six reddish bands, three on each side. The two inner bands are almost spotless; the two central ones are marked by a chain of small spots and points of velvet-black; the exterior bands are marginal, and each subdivided by a black fillet. The abdomen is of an olive colour, broadly bordered and spotted with black. Savigny distinguishes, under the name of S. officinalis (it is

the H. provincialis of Carena), another species, likewise used in medicine, and frequently confounded with the preceding (fig. 19). It is vulgarly known as the green leech, and resembles

¹ Cuvier seems to express no very decided opinion on the subject above referred to. "On voit dans plusieurs en dessous du corps deux séries de pores, orifices d'autant de petites poches intérieures que quelques naturalistes regardent comme des organes du respiration bien qu'ils soient la plupart du temps remplis d'un fluide muqueux" (Régne Animal, t. III., p. 213). Dr Williams has more recently shown that the so-called pulmonary vessels are in fact ovario-uterine organs.

² We observe it stated in several continental works of authority, that leeches are unknown in, or at least not indigenous to, the western world. We were inclined a priori to doubt the accuracy of this statement, and lately instituted some inquiries on the subject, in which we were aided by an excellent physiological naturalist, Dr Allen Thomson. We find that in the Dispensatory of the United States, by Drs Wood and Bache (published at Philadelphia in 1833), there is a description of a true American medicinal leech. These authors state, that at New York, Boston, and elsewhere, European leeches, that is, the gray and green varieties of the Hirudo medicinalis of Linnæus, are chiefly employed, and are imported in great quantities; but that in Philadelphia and the neighbourhood the indigenous Hirudo decora is used. It is this species which is described in Major Long's Second Expedition (vol. II., p. 269). The back is of a deep pistachio-green colour, with three longitudinal rows of square spots, twenty-two in number, and placed on every fifth ring. The abdomen is spotted with black. This kind usually measures two or three inches in length, occasionally attaining to the extent of four or five inches. It is carried to Philadelphia by the country people from Bucks and Berks county. It is said to draw less blood than the European leech, and does not cut so deeply. About three American do not more than correspond to a single European leech in their sectorial powers.

³ The eyes of leeches are easily detected by the assistance of a lens, under the form of a semicircular row of black points, situated above the mouth, upon the sucking surface of the oval disk, a position evidently calculated to render them efficient agents in detecting the presence of food. According to Professor Müller, they do not exhibit any apparatus of transparent lenses adapted to collect or concentrate the rays of light, but each ocellus, or visual speck, would seem to be merely an expansion of the terminal extremity of a nerve

the common kind in size, and the number of its segments; but the colour of the back is not so sombre, and the abdomen is of a more yellow green, and, though bordered with black, is without spots. The six anterior eyes are very projecting, and have more truly the appearance of organs of vision. The third species mentioned by Savigny is the S. granulosa. It was brought by M. Leschenault from Pondicherry, where it is used in blood-letting after the manner of our European kinds. S. obscura and interrupta are both described by M. Moquin-Tandon as indigenous to the vicinity of Montpellier; and S. verbena of Carena occurs in the Lago Maggiore.

With the exception of the last-named species, and that from Pondicherry, M. Blainville refers all the others to the H. medicinalis of Linn., of which, according to his peculiar views, he establishes five varieties; the grey, the green, the spotted, the black, and the flesh-coloured. With that love of change for which too many modern naturalists are remarkable, he names the genus Jatrobellia.

We have already mentioned that leeches are abundant in all the countries of Europe. France furnishes an immense supply, and their collection in some of her provinces affords the materials of an important branch of commerce. Some curious details on the subject were read several years ago to the agricultural society of the department of Seine-et-Oise. Towards the month of April or May, according to the nature of the season, the country people collect the cocoons or capsules formerly mentioned as containing the eggs. These they find in abundance in the mud of shallow marshes, and convey them to various reservoirs in other quarters, so as to spread and propagate the breed. They do not use them commercially till they are about eighteen months old. Leeches are very numerous in the lakes and marshes in the neighbourhood of Nantes; and their collection is carried on throughout the whole year, but chiefly during summer. They are transported to Paris in linen bags, each containing about 500, placed in panniers, and surrounded by wet moss. During a favourable season the dealers of Nantes will sometimes receive at the rate of fifty thousand every day; and a Parisian druggist informed M. Audouin, that in the summer of 1820 he received from Moulins 130,000 for his own share.¹ Four of the principal dealers in London are said to import between seven and eight million of medicinal leeches every year. Many leeches refuse to bite. This generally arises either from their appetite for food having been recently satisfied, or from their being about to change their skins. It is believed, however, that capricious individuals sometimes occur, which will not suck at all; and of this it is impossible to ascertain the cause. Inflammation occasionally follows the infliction of the bite, and in this case a vulgar prejudice exists that a horse-leech has been applied. This is in every way an error, for the horse-leech refuses to fasten upon the human body. The means used for the preservation of leeches in confinement are various. The most common mode consists in placing them in a bottle of water frequently renewed. Some apothecaries find advantage from placing moss or aquatic plants at the bottom of the vessel, which aid in freeing them from slime. The chief dispenser of the marine hospital of Rochefort keeps his

leeches simply in moistened clay, in which the creatures Annelida form holes and galleries, where they live happily for years.

Mr Brightwell states that a dealer in Norwich keeps a stock of about 50,000 in two large tanks of water, floored with soft clay, in which the creatures burrow. On examining these tanks he found many capsules or ova deposits of the leech, which the owner, ignorant of their nature, stated to be at times very numerous, but which he neglected, and indeed generally destroyed.

(The curious in leeches may consult the following works, in addition to those already quoted:—Histoire Naturelle et Médicale des Sangsues, &c., par T. L. Derheims, 8vo, Paris, 1825; Observations sur la conservation et la reproduction des Sangsues, par Chatelain, 8vo, Paris, 1826; Monographie des Sangsues Médicinales et Officinales, par A. Charpentier, Paris, 1838; Sur la Multiplication des Sangsues, par T. B. Hazard, 8vo, Paris, 1841. See also some observations On the Minute Anatomy of the Horse leech, by J. E. Quekett, in the Zoologist, pp. 17, 88, 324.)

GENUS HÆMOPIS, Sav. Differs from the preceding chiefly in the jaws being not compressed, and furnished with less numerous dentations.

H. sanguisorba, Sav. (Hirudo sanguisuga, Linn.), commonly called the horse-leech, is a well-known species, somewhat larger than the medicinal kinds, and of a uniform greenish-black colour. A great diversity of opinion seems to exist regarding the blood-drawing propensities of this species. Many allege that it causes wounds extremely dangerous both to man and beast. Linnaeus asserts that nine will kill a horse. MM. Huzzard and Pelletier, on the other hand, maintain that the horse-leech, improperly so called, never attacks any vertebrated animal whatever;² while M. de Blainville again is of opinion that these writers have mistaken their subject of observation, and have described the black leech (his Pseudobdella nigra), which is truly characterized by the jaws being nothing more than folds of toothless skin, and may therefore be inferred to confine its attacks to the lower orders of creation. We agree with Cuvier in thinking that the subject deserves a fresh examination. In addition to the common species, Savigny describes three other kinds,—H. nigra, luctuosa, and lacertina.

GENUS BDELLA, Sav. Dentations of the jaws entirely wanting. Eyes only eight in number.

As far as we know, this genus consists of only a single species, the Bd. Nilotica (fig. 20), found in Egypt, and familiar to the Arabs under the name of Alak. It appears to have been known to the ancients; and Herodotus (Hist. lib. ii., cap. 68) describes it as a parasite of the crocodile. It is of a chestnut-brown colour above, of a lively red below.

GENUS NEPHELEIS, Sav. In this genus the eyes are also only eight in number, the four anterior being disposed in a crescent form, the four posterior ranged on each side on a transverse line. The jaws are reduced to three simple folds.

Savigny describes three species, N. rutila, tatacea, and

derived immediately from the brain, spread out beneath a kind of cornea formed by the delicate and transparent cuticle, behind which is a layer of black pigment, to which the dark colour of the ocular points is due. We ourselves entertain no doubt that leeches have eyes, but the evidence (from written authorities) is very contradictory. Weber was the first to show the true nature of the black specks in H. officinalis (Meckel's Archives, 1827, p. 301). More recently Wagner (Lehrbuch d. vergleich. Anat. 1835, p. 428) has described, in the interior of the pigment layer, a transparent body, composed of two parts, which he regards as consisting of a crystalline lens and a vitreous portion. Brandt has even traced the ten optic nerves from the brain to the eyes (Med. Zool. I., p. 250). On the other hand, Moquin-Tandon, in the revised edition of his work (Monographie des Hirudines, Paris, 1846), states that these black specks contain neither lens nor vitreous humour, although they are light-receiving organs; while Leydig (in Siebold and Kolliker's Zeitsch. I., 1849, p. 103) goes so far as to assert, in relation to the alleged eyes of the parasitic genus Piscicola, that they neither receive a nerve, nor contain a light-refracting body. He regards them as simple ornaments, analogous to the corresponding pigment dots on the pedal shield, with which they also correspond both in colour and distribution.

¹ Dict. Class d'Hist. Nat. t. xv., p. 108.

² Journal de Pharmacie, Mars 1825.

Annelida, cinerea. The two former occur near Paris; the last named is frequent in the marshes of the forest of Fontainebleau. Of Nephtelis tessellata, Müller observes that the female is sometimes found filled with 300 young. N. vulgaris is frequent in our fresh waters, and the brown capsules containing the ova may be found on the underside of the leaves of many water plants, among the ova of the helices. Mr Brightwell kept several species through the summer, and carefully observed the deposition of the ova, and development of the young. On the 2d of June N. vulgaris deposited one capsule containing ova, on the 5th another, on the 10th a third, and on the 15th two more, each containing from seven to ten eggs. On the 22d the young appeared in the capsule deposited on the 2d, and on the 13th July they emerged from the capsule, and in six weeks they left it, fully developed. He detected rotiferous animalcules in their stomach.

The genus TROCHETIA of Dutrochet does not seem to differ from the preceding, except by an enlargement near the position of the generative system. One species (Geobdella trochettii of Blainville) comes on shore in pursuit of earth-worms. Another minor genus has been established by M. Moquin-Tandon, under the name of AULASTOMA. The jaws are represented by numerous projecting folds. The eyes are ten in number. We may here also mention M. Odier's genus BRANCHIOBDELLA, of which the jaws are two in number, and the eyes wanting. It inhabits the gills of cray-fish.¹

In all the preceding groups or genera of leeches, the anterior sucker is but slightly distinguishable from the adjoining portion of the body; but in the two following genera it is rendered more perceptible by a restriction, and is composed of only a single segment. In the genus HÆMOCHARIS of Savigny, the eyes are eight in number, the body slender, and indistinctly ringed. The species do not swim, but march after the manner of the surgeyors or geometric caterpillars. They attach themselves particularly to fishes. The genus ALBIONE of the same author differs from the preceding in its body being beset by tubercles, and in possessing only six eyes. The species inhabit the sea. We may mention, as an example, the Hirudo muricata of Linn.

The genus BRANCHELLION of Sav. is distinguished by what some regard as projecting branchiæ. The epidermis is loose and ample, and seems to enclose the animal as in a sack. The species are parasitical, and attach themselves chiefly to fish of the torpedo kind. With the leeches, Cuvier also places the genus CLEPSINA, Sav., which is charac-

terized by a broadened body, possessing only a posterior sucker. The anterior portion is a simple orifice, without any appearance of the usual disk. The species make a near approach to the Planaria, and the one represented by the annexed cut was described and figured by Mr Kirby, under the name of Hirudo crenata (fig. 21).² The development of the ova in this genus has been described by Grube.³ C. complanata usually deposits from five to seven ova, enveloped in a very transparent, soft, succular egg-case, while in C. bioculata there are only three or four, and in C. marginata only a single ovum in each capsule. These egg-cases are glued by a peduncle to water plants, and continue hanging thereto, but the young, when excluded, attach themselves to the abdomen of the mother. Other genera, allied to the preceding in their enlarged form and absence of the oral disk, have been established by Oken and Blainville. Of these, however, we cannot give account within our prescribed limits, and we shall therefore conclude the present treatise by a short notice of the more distantly related.

GENUS GORDIUS, Linn. Body filiform, smooth, or with very slight transverse markings. Neither branchiæ nor tentacula of any kind.

A well-known species of this genus (G. aquaticus, Linn.) is distinguished in this country by the name of the hair-eel. It occurs in springs and marshes, and among moist sand, and also dwells in mud, which it perforates in all directions. It is believed by some to be parasitic in the abdominal cavity of many insects. A list of these latter, so infested, has been published by Professor Siebold (Entomologische Zeitung. Jahrg. 1843, p. 77). The position of the genus is variously regarded by different naturalists, and the extreme tenuity of form in these creatures has probably opposed obstacles in the way of a precise knowledge of their structure. The nervous system being composed of a ganglionic cord, seems, however, a strong reason for placing them among the Annelida. We follow the Baron Cuvier in so doing, although we are aware that Rudolphi and Blainville combine them with the genus Filaria, which contains the noted Guinea worm (P. Medinensis), and is usually regarded as belonging to the intestinal class. (s. w.)

Fig. 21

INDEX.

¹ Mém. de la Soc. d'Hist. Nat., t. i., pl. iv.

² Linn. Trans. ii., tab. 29 p. 312.

³ Zur Anatomie und Physiologie der Kienstwürmer, Königsberg, 1838.