It is scarcely necessary to say that this was not a notion which can be traced back to the earliest ages of the Christian church, and that the creed of the first believers was in this respect in complete antagonism with the idea which brought the Jews year by year to Jerusalem for the celebration of the Passover. The local ritual which belonged to the only temple known to the Jews had for them been displaced by a purely spiritual worship, which proclaimed that men were as near to God in one place as in another. In whatever channel their feelings might otherwise have run, the circumstances of the Christian church in the first century left absolutely no room for the development of local association. Yet a few years, and the history of this weary world would be closed by the return of the Son of man to judgment, and by the summons which should call the dead from their graves. But the course of events which led to the establishment of Christianity as the religion of the Roman empire insured the growth of a sentiment far more nearly allied to that of the Jewish pilgrims, when gathered for the great annual feast in the city of David. The Christian converts in Rome and Corinth, in Athens and Alexandria, had been worshippers of the Capitoline Jupiter, or the Olympian Zeus, of Isis and Osiris, of Phaebus, Artemis, or Mithras. That these converts had undergone a vast change for the better we need not and we cannot doubt; but the framework of their old associations had not been broken, and the men who had followed the jotirneyings of Phaebus from his birthplace in Delos to his final home in Delphi, might now with feelings immeasurably deeper and more earnest move from spot to spot noted, in the gospel narratives, until the pilgrimage begun in the grotto of Bethlehem ended on the mount of the ascension. The whole of Palestine thus became sacred soil, but for a time the rapid growth of this local veneration called forth something like remonstrance or warning. Teachers like Augustine could remind their hearers that they were not to seek righteousness in the East, nor mercy in the West, and that a voyage to the Holy Land was a useless task for men whose faith placed them at once in the immediate presence of their Lord. But the practice of some among them was not altogether consistent with their precepts. Jerome could insist that heaven was not more easily approached from Palestihe than from Britain; but the saint had crossed the sea to take up his abode in a cave at Bethlehem, and had no rebuke to offer to the Roman ladies who followed him, partly to feast upon his eloquence, and in part to derive strength and comfort from contemplating the scenes of the Saviour’s ministry. Such feelings seldom fail to provide their own „nourishment. The vehement devotion stirred by the sight of Calvary would impart a priceless value to that instrument of punishment which by bearing the body of Jesus had become veritably a tree of life; and in due time the yearning for this relic was rewarded by its discovery. Its genuineness had been attested by the healing of a dying woman who derived no benefit from touching the crosses to which the two thieves had been fastened; and the great churches built by the first Christian emperor and his mother over the Holy Sepulchre and the Cave of the Nativity became sanctuaries which the Christians regarded with a devotion immeasurably more passionate than that which the Jews felt for the temple at Jerusalem. The stream of pilgrims, which probably had long been gathering volume, now swelled into something like the proportions of a flood; and each man found not merely that he could worship on spots which brought him nearer to heaven, but that the devotion of the faithful had done or was doing much to smooth the difficulties or lessen the dangers of his journey. It was not wonderful that the enthusiasm thus fostered should give birth to convictions which no calamities could destroy or even shake. According to this new belief the shirt which the pilgrim wore when he entered Jerusalem would, if used as his winding-sheet, carry him straight to heaven. His death, if it happened during his sojourn in Palestine, made him an object of envy to his kinsfolk and friends. If he returned home, he was treated as one whose sins had been washed away, and perhaps as the bearer of relics whose virtues were so potent as to make the weary journey to Jerusalem a work of supererogation.

The tide of pilgrimage thus flowing steadily onwards was first arrested by the armies of the Persian king, Khosru III., the grandson of Nushirvan. Jerusalem was taken, 611 a.d.; 90,000 Christians, it is said, were slaughtered; and the disaster was crowned by the carrying away of the true cross into Persia. Marching on into Egypt, Khosru received a letter from a citizen of Mecca, charging him to acknowledge Mahomet as the prophet of the one God. He tore the letter into shreds. Mahomet replied only by warning him that his treatment of the letter was a sign of the way in which his kingdom would be treated by-and-by. The punishment of Khosru was to come, however, not from Mahomet, but from the Emperor Heraclius, who, waking from the sluggish inactivity of the earlier part of his reign, defeated the Persians in the passes of Mount Taurus, and destroyed the birthplace of Zoroaster. In tho end Khosru was murdered by his son Siroes, from whom Heraclius recovered the true cross by a treaty which also delivered those of his subjects who had been taken prisoners by the Persians. In the following year, 629, Heraclius himself knelt among the worshippers in the church of the Holy Sepulchre. Eight years later, 637, the disciples of Mahomet, now lords of Damascus, laid siege to Jerusalem; but after a blockade of four months a treaty made with the caliph Omar in person secured to the Christians not merely the safety of their persons and goods, but the free exercise of their religion, subject only to the conditions that Mahometans should have the right of admission to their churches at all hours; that the cross should not be seen on the exterior of any building, or be carried about the streets; and finally, that the Christians should be disarmed, and should show respect to their conquerors by wearing a distinguishing dress and by rising up at the approach of true believers. The hardships thus imposed may have been sensibly felt; but pilgrims and merchants still came and went practically without let or hindrance; and even the attack of the Fatimite caliph Hakem, four centuries later, 1010, scarcely changed things for the worse. The rule of his predecessors in Egypt had for the Christians been lighter than that of the Abbasside caliphs of Baghdad; but the object on which the mad Hakem had set his heart was nothing less than the destruction of the great Christian sanctuary. Such persecution as there was fell on the Jews only, and the tax imposed on each pilgrim and levied on his entering Jerusalem was pïobably not resented as a wrong. To the wealthier Christians it brought an opportunity for securing a higher degree of merit by paying the charge for their poorer brethren; while the completion of the first Christian millennium removed a burden which had lain with increasing heaviness on the spirits and energies of men, and gave a fresh impetus to the feeling which carried the devout to the Holy Land. The end of the 10th century, it was almost universally believed, would be the end of the world. The beginning of a new age relieved them of this mental incubus, and the stream of pilgrims became larger than ever. The path followed by these devotees was not always strewn with roses. Inclement seasons, poverty, and sickness proved fatal to many; but these disasters were not caused by the attack of open enemies, and the conversion of Hungary removed a formidable obstacle for those who had to traverse the heart of Europe in order to reach Palestine.

A few years later these fairer prospects were permanently clouded by the advance of the Seljukian Turks, who in their inroads into the Eastern empire found themselves effectually aided by the subjects of the emperor. Thecauses of discontent were indeed many and deep. Extortion and tyranny, both secular and ecclesiastical, had alienated thousands, while the population was seriously lessened by the accumulation of land in the hands of a few owners. Before the close of the Γlth century, 1076, Jerusalem had opened her gates to the Seljukian Toucush; and in place of a legal toll the pilgrims found themselves subjected henceforth to indefinite extortion, to wanton insult, and to massacre. The sanctuaries of the Christians were profaned, their worship was interrupted, their patriarchs were thrown into dungeons. The effect of these changes was felt not by the devout only. The supplying of their wants had called forth the energies of merchants; and the fleets of Genoa, Pisa, and Amalfi hurried to the ports of the Holy Land for the great Easter fair at Jerusalem. All these were now driven away, and there remained only the miserable train of pilgrims, who returned to Europe, if they returned at all, with tales of dire indignities done to men, women, and children alike.

The recital of these wrongs went far towards fanning into flame the feelings which the popes had hitherto failed to waken in sufficient strength. The idea of an armed host which should inflict summary vengeance on the oppressors of the Christians had already dawned on the mind of the great Hildebrand, Gregory VII.; it had been vehemently urged by his successor Victor III.; but neither had struck the right chord. Such enterprizes can never be set in motion, with any solid results, except when the flood tide of popular feeling gives its own weight to the sanction of religious authority. Nor was this result more satisfactory when, in 1081, Robert Guiscard set out from Brundusium (Brindisi) with a fleet of 150 ships and a force of 30,000 men. Guiscard himself besieged Dyrrhachium (Durazzo) in vain; under his son Bohemond his fleet was miserably defeated. Four years later Guiscard made another attempt, which was frustrated by his death at Cefalonia (Kephallenia). But Hildebrand had been dead only ten years when a vast throng of clerks and laymen was gathered to meet Urban II. at Piacenza (Placentia). In Italy, however, Urban felt that he could not look for the enthusiasm which would justify him in making the final venture. From Piacenza he made his way to his old home in the great abbey of Cluny, and in the autumn of 1095 appeared at Clermont, in the territories of the count of Auvergne.

Here he found that there was no longer any need of holding back. To the north of the Alps the indignation of the people had been roused to fever heat by the preaching of Peter the Hermit. With the stature and ungainliness of a dwarf, emaciated by the austerities of his self-imposed discipline, this man, who had forsaken his wife and abandoned his military standard under the counts of Boulogne, had returned from the Holy Land with his heart on fire, not so much from the memory of the hardships which he had himself undergone as for the cruelties and tortures which he had seen inflicted on his fellow-Christians. Simeon, the patriarch of Jerusalem, to whom he first betook himself, could only bewail the weakness of the emperor and of his government. “The nations of the West shall take up arms in your cause,” was the reply of the hermit, who soon afterwards, armed with the special blessing of Urban II., mounted his ass, and with bare head and feet, carrying a huge crucifix, traversed the Teutonic lands, rousing everywhere the uncontrollable indignation which devoured his own soul. His vehemence carried all before him, none the less, perhaps, because he bade them remember that no sins were too heinous to be washed away by the waters of the Jordan, no evil habits too deadly to be condoned for the one good work which should make them champions of the cross. Urban, however, and his counsellors, knew well that before the fatal die could be prudently cast a serious task lay before them. The system of feudalism substituted personal ascendency for the dominion of law; and wherever the personal bond failed, the resort was inevitably to private war. The practice of such wars had become virtually an organized trade; and if a large proportion of the population should be drawn away to fight against the infidel in Palestine, those who remained at home would be without defence. Such wars were therefore formally condemned; the women and the clergy, merchants and husbandmen, were placed under the special protection of the church, and the Truce of God was solemnly confirmed. The nearer and more immediate dangers being thus guarded against, Urban from a lofty scaffold addressed the assembled multitude, dwelling in the first place, and perhaps not altogether prudently, on the cowardice of the Turks, and on the title to victory which birth in a temperate climate conferred on the Christians. They were thus sure of success, and sure, too, to win an infinitely higher blessing—the remission of their sins. Sufferings and torments more excruciating than any which they could picture to themselves might indeed aw ait them; but the agonies of their bodies would redeem their souls. “Go then,” he said, “on your errand of love which will put out of sight all the ties that bind you to the spots which you have called your homes. Your homes, in truth, they are not. For the Christian all the world is exile, and all the world is at the same time his country. If you leave a rich patrimony here, a better patrimony awaits you in the Holy Land. They who die will enter the mansions of heaven, while the living shall pay their vows before the sepulchre of their Lord. Blessed are they who, taking this vow upon them, shall obtain such a recompense; happy they who are led to such a conflict, that they may share in such rewards.” With the passionate outburst, “It is the will of God, it is the will of God,” the vast throng broke in upon the Pontiff’s words. “It is, indeed, His will,” the Pope went on, “and let these words be your war-cry when you find yourselves in presence of the enemy.

Vou are soldiers of the cross; wear then on your breasts or on your shoulders the blood-red sign of Him who died for the salvation of your souls.”

So was sanctioned the mighty enterprize which hurled the forces of Latin Christendom on the infidels who had crushed the East under the yoke of Islam; and so it received its name. Of the thousands who hastened to put on the badge the greater number were animated probably by the most disinterested motives, while some had their eyes fixed on the results of more politic calculations. For the multitude at large there was the paramount attraction of an enterprize which the abbot Guibert boldly put before them as a new mode of salvation, which enabled the layman without laying aside his habits of wild licence to reach a height of perfection scarcely to be attained by the most austere monk or the most devoted priest. Nay more, the assumption of the cross set the debtor free from his creditor so long as he wore the sacred badge, opened the prison door for the malefactor, annulled the jurisdiction of the lord over the burgher or the peasant, and enabled the priest and the monk to escape from the monotony of the parish and the cloister. It might be thought that these privileges would tell hardly on the creditor, the capitalist, and the usurer; but these reaped the most solid benefits. The princes who bound themselves by the vow must provide equipments for themselves and their followers, and carry with them sums of money sufficient for their needs. These sums must be raised by loan or mortgage; and as all wished to get horses, arms, and money in exchange for lands, the former became inordinately dear, the latter absurdly cheap. Thus the real gain lay on the side of the merchant and the trader, or of the landowner who was prudent enough to add to his own domains by availing himself of the necessities of his neighbour. All this, however, had been effected by the a it hority and sanction of the Holy See, which had taken under its protection the dominions of all crusading princes. It was for the Pope to decide whether those who had taken the vow should set off at once, whether some grace time should be allowed, or whether the vow should be remitted altogether. The Pope became therefore possessed of a dispensing power which placed him virtually above all other sovereigns. His gains, moreover, were immediate. The crusades tended, beyond doubt, to merge the smaller into larger fiefs, which again were absorbed into the royal domain, thus largely promoting that growth of the sovereign power which in the end broke up the feudal system. Those results belonged to the distant future; but the Pope was enabled, rather he was constrained, to send his legates into every land, both to enlist soldiers under the standard of the cross, and to collect money for their support. He became thus at once the administrator of vast revenues which were raised partly by subsidies imposed as a necessary obligation on the clergy, and in part by the voluntary contributions of the laity. With the Pope the ecclesiastical body generally acquired enormous power. The lands of the church, though money might be borrowed upon them, could not be alienated; but it was only in comparatively a few instances that it was necessary to burden them at all. The monastic houses might send some of their members to the Holy Land; the rest remained at home, and became mortgagees or trustees of estates belonging to the crusaders. If these died without heirs, the guardians became absolute owners; and of those who returned not a few withdrew into the cloister, and endowed with their worldly goods the community which they joined.

In the enterprize sanctioned by the Council of Clermont, no nation, as such, took any part; and this fact serves perhaps to explain the measure of its success and its failure. Had it been necessary to wait for strictly national action, the work perhaps would never have been done at all; but had it been a national undertaking some attempt must have been made to establish a commissariat, and to insure something like harmonious and efficient generalship. As it was, the crusading army was simply a gathering of individual adventurers who depended on their own resources, or of reckless pilgrims who neither possessed nor cared to provide any. The contributions made to this army by the different countries of Europe varied largely. From Italy, where the charm was in great part dispelled by the struggle between Pope and anti-Pope, few came besides the Normans who had fought under the standards of Robert Guiscard. The Spaniards were fully occupied with a crusade nearer home, which was to turn the tide of Mahometan conquest that had once passed the barriers of the Pyrenees and threatened to flow onwards to the shores of the Baltic. In Germany there was no great eagerness among partisans of emperors whom popes had sought to humble, to undertake a difficult and dangerous pilgrimage. In England the condition of things which followed the victory of William over Harold prevented both the conquerors and their subjects from...

The Crustacea belong to the sub-kingdom Annulosa, and to the division Arthropoda, in which are also included the Insecta, the Myriapoda, and the Arachnida ; they are known also as Articulata, from the body being composed of a series of distinct rings or segments, each segment usually possessing a pair of jointed appendages or limbs articulated to it. They may be defined to be those Articulata which, whenever respiratory organs ⅛re specially developed, possess branchiae and not tracheae. By this definition they are at once separated from all insects and myriapods, which invariably possess tracheae. But it remains a difficulty, if it be not altogether impossible in the present state of science, to frame any definition which shall similarly include all Crustacea and exclude all Arachnida. In both classes, in fact, there are forms which possess no special respiratory organs; and if in these cases we resort to other characters, none which are of universal application have as yet been discovered.

It may be said, however, that as a rule these exceptional Crustacea possess more than four pairs of locomotive appendages, have two pairs of antennary organs, and possess a simple alimentary canal; while the Arachnida generally have not more than four pairs of locomotive appendages, possess at most one pair of antennary organs, and have their alimentary canal produced into caeca (Huxley).

External Structure. —The skin of the Crustacea is more or less completely hardened by a horny deposit called “chitine,” with or without the addition of lime, ] thus forming a defensive covering to the softer tissues of the animal. This hardened envelope serves also as an external skeleton, giving rigidity and support to the internal organs; and to its inflections, projections, and rugosities the muscles and membranes of the body and appendages are attached.

Body-Segments. —The crustacean exo-skeleton consists of a series of rings, usually a repetition of each other, and differing only in modification according to the necessity of the various portions of the animal. Each of these divisions is called a somite (Huxley).

The normal number of somites, or segments, is twenty-one; but instances occur among the extinct Trilobita and the recent Phyllopoda and Branchiopoda, in which a larger number of segments than twenty-one· are to be met with. On the other hand, many recent and fossil forms offer examples of Crustacea in which one or more segments are never developed; but this apparent absence is generally due to their coalescence, and we shall not unfr§quently find indications of this if we bear in mind the theory of Oken, that each pair of appendages indicates a separate segment. A knowledge, too, of the earlier (larval) stages of some of these forms has revealed the presence of the normal number of free segments in the young individual, which in later life are permanently soldered together.

Although the segments of tho Crustacea are greatly modified in the different orders, yet they can nevertheless be shown to be all composed of two lateral moieties resembling each other; we can also distinguish two arcs, the one superior, the other inferior, as shown in tho annexed figure (fig. 2).

The superior central pair united constitute the tergum (í, t), and the lateral are called the epimera (ep, ep).

The inferior arc is composed of the same number of pieces. The two median pieces unite to form the sternum (s, s), and the latero-inferiorpair are called the episternum (es, es). They are always united at the sternum; but there generally exists, between the inferior arc and the epimera situated above, a wide space destined for the articulation of the corresponding appendage (Milne-Edwards).

Mr C. Spence Bate, in his “Report on the British Edriophthalmia” (Brit. Assoc. Repts., 1855), differs from Milne-Edwards and other previous writers who had considered the series of scale-like plates at the sides of the body-segments of the Amphipoda as representing the “epimeral pieces” of each somite; on the contrary, he considers them to be the dilated coxal joint (or protopodite) of each limb. This view he adheres to in his chief work (1863, p. 3) on the sessile-eyed Crustacea, and reiterates in his Report (1875, p. 47), where he writes the epimera as sectional pieces in a theoretical construction of a somite cannot exist; they are really portions of the integument of the appendages. That they are present in the Amphipoda attached to the coxal joint of seven pairs of the limbs is readily seen; but in the Decapoda, Stomaρoda, and Isopoda it cannot by any means be so easily demonstrated. “We know of no example of a ring in which we are able to distinguish all the pieces that we desire to enumerate. In some there is an absence of certain pieces from the places they should occupy; sometimes they are very intimately soldered together, so that we cannot detect even a trace of separation; but in studying each of them separately, where it is most distinct, we shall be able to form a clear idea, and recognize its character in spite of its union with its neighbouring pieces. Moreover, although this analysis of the ring may not be always practicable, it is none the less true that it facilitates much the study of the exterior skeleton of articulated animals, and that it will permit us often to establish analogies where the greatest difference would at first sight appear to exist” (Milne-Edwards).

Professor Huxley in his lectures has somewhat simplified Milne-Edwards’s view of the crustacean segment. Taking for his type one of the body rings, or somites, of the common lobster (fig. 3), he points out that it consists of a convex upper part, called the tergum (∕), and a flatter inferior side, the sternum (s), the angle of junction on each side of the tergum and sternum being produced downwards, forming what is termed the pleuron (or epimer α) (y>Z.) For ordinary studies this view of a somite will be found sufficiently clear and simple.

From the inner surface of these tegumentary rings in the Crustacea various plates are given off which project into the internal cavity, constituting in some instances cells and canals.

According to Milne-Edwards, these processes are always developed at the points of union of two rings or of two neighbouring pieces of the same segment; and this disposition has obtained for them the name of apodema (fig. 4). They are the result of a fold of the integumentary membrane which penetrates more or less deeply between the organs, and which is strengthened with calcareous matter like the rest of the external structure, and always formed of two thin plates soldered together. They serve the office fulfilled by the bones in the Vertebrata, viz., that of affording solid surfaces to which the muscles are attached.

Divisions of the Body in the Crustacea.— By general consent and usage the body of a crustacean is divided into three regions, namely, head (or cephalon), thorax, and abdomen (see figs. 1 and 6), to each of which divisions seven out of the twenty-one segments are attributed. These terms are used as a matter of convenience, and are not assumed to be homologous with the grand divisions of head, thorax·, and abdomen, in the Vertebrata. All writers agree in considering the last seven segments to be abdominal. The only difference of opinion is as to the division of the first fourteen,—how many are cephalic and how many thoracic.

Dr Dana is of opinion that Crustacea have no distinct head, but only a cephalothorax composed of the fourteen anterior segments, yet he admits that in the Edriophthalmia the seven most anterior pairs of appendages are devoted to the mouth and organs of sensation, and in the extinct Pterygotus and in the Trilobita a distinct head certainly exists.

Professor Huxley considers that the division in the Podophthalmia is indicated by the cervical fold and by the sudder change in the character of the appendages between the sixth and seventh somites, and an equally marked similarity between the latter and those of the eighth and ninth pair. So that according to this view we should have six cephalic, eight thoracic, and six abdominal somites (for Professor Huxley regards the telson as not being a true somite but a median appendage, like the post-oral plate in Pterygotus). But, as Dana well observes, the mouth organs may become legs, or the legs may become mouth organs by slight variations, therefore this line of division can hardly be maintained on the character of the appendages alone, seeing it does not hold good for other groups equally entitled to consideration, as is the Podophthalmia.

The subjoined table may serve to show these several views more clearly :—

Arrangement and Nomenclature of the Somites or Bodyrings of the Crustacea, with their Appendages. [table]

The Appendages. —Just as we find a typical number of twenty-one body srgments to prevail among the Crustacea, so also in the appendages the type number of joints is seven, any departure from which is disguised by fusion of one or more joints together, the obsolete condition of others, or the depauperization of the limb into numerous articuli (see fig. õ). At the coxal joint, or protopodite, each limb usually bifurcates; firstly, there arises the external limb proper, or exopodite, which is normally seven-jointed; and secondly, the internal branch, or endopodite, which may serve as a mouth organ, a branchial appendix, a swimming organ, or a protection for the ova or the young. The appendages belonging to the three divisions of the body differ from each other in a greater or less degree in proportion to the higher or lower grade which we examine. Thus among the Decapoda (crabs and lobsters) the cephalic, thoracic, and abdominal somites all possess appendages with well marked characters, each series being highly differentiated for the functions to be performed by it. Among the Entomostraca, the appendages of the anterior cephalic somites alone are highly specialized, the others being either mere vegetative repetitions of one another, or else altogether wanting.

First pair.— The first cephalic somite supports the eyes, the most constant of all the organs, and probably the only pair of appendages which are never diverted from their normal use, though sometimes atrophied. In the more highly cephalized forms, the Decapoda-Brachyura (crabs), the eyes are placed on the outer s i de of the two pairs of antennae, but the anatomical evidence shows that the most anterior pair of nerves, in this as in all other orders of Crustacea, is that which is connected with the ophthalmic organs.

Second pair.— The second somite bears the first pair of antennae (or ardennules), called the inner pair in the higher forms, and the upper pair among the lower Crustacea. Ordinarily they are slender, tapering, freely-moving, multi-articulate organs. In the lobster both the endopodite and exopodite are equally developed from a common basal-joint or protopodite (see 2 in fig. 6).

Third pair.— The third somite supports the second or posterior pair of antennae, sometimes called the outer pair in the higher, and the inferior pair in the lower forms of Crustacea. In the lobster these are represented by a basal-joint or protopodite, and a long filamentary, multi-segmented endopodite, to the outer base of which a small scale is attached representing the exopodite. In all the higher Crustacea the three most anterior somites are always praeoral, being in front of the buccal orifice, and in most genera, moreover, they are specially set apart as bearing the organs of sense. Generally they are so closely blended together, both in the earlier stages of development and also in the adult forms, as to defy separation, the presence of three somites being only demonstrable by dissection, and by a knowledge of the fact that each pair of appendages, wherever it exists, presupposes a segment or ring to which it belongs. The genus Squilla affords, perhaps, the best evidence of the separate existence of these cephalic rings. In it the first, or ophthalmic somite, is quite distinct from the second and third antennary, which are also separable from one another, although the latter blends with the next somite, and the succeeding ones can only be distinguished by dissection. Usually the antennae or feelers are constant appendages; but still, the number and disposition of these organs varies extremely. Some of the lowest forms are wholly without antennae, or are furnished with them in a merely rudimentary state. Some species have only a single pair, the normal number, however, as we have already pointed out, is two pairs. In position they are inserted on the superior or inferior surface of the head, according to the development of the somites composing the cephalon. Ordinarily they are slender flexible multiarticulate appendages, but even among the higher forms they are subject to extraordinary modifications; thus in the Scyllaridae, the external pair are developed into broad flat organs of natation, and probably also for burrowing. In Arcturus, an Isopod, they are the nursery for the young; in the Entomostraca they are usually natatory organs; in Pterygotus and Limulus they are chelate, serving, as in the Copepoda, as clasping organs for the male. In the last free condition of the Cirripedia and Rhizocephala they serve as the organs for attachment,—being converted into cement-ducts in the former, and into root-like organs of nutrition in the latter. The second pair of antennae and sometimes even the first pair become mouth organs in the Merostomata.

Fourth to Ninth pairs. Epistomial or Mouth Organs.— In the Decapoda the six succeeding pairs may be called mouth-organs or epistomial appendages, being all engaged in duties subservient to nutrition. The fourth somite bears the actual jaws or mandibles proper with their palpi, outside which lie two pairs of maxillae, followed by three pairs of maxillipeds or jaw-feet. In each successive somite, these organs become less highly specialized mouthorgans, and betray the fact that they are after all only simple feet modified. Thus in Squilla (a Stomapod) the eighth somite (first thoracic) bears a pair of robust claws, the terminal joint of which is furnished with long and sharp teeth, these forming the.principal organs of prehension; whilst the ninth somite bears a pair of ordinary feet like the two following pairs (see fig. 71).

In most of the Edriophthalmia the mouth-organs extend only to the seventh somite, the eighth and ninth being included with the ambulatory members.

In the Decapoda we can detect the more or less rudimentary endopodite and exopodite in the fifth pair of appendages, and in each succeeding pair to the ninth; the eighth and ninth pairs also bear a third organ called an epipodite, and a gill or branchial organ.

Tenth to Fourteenth Pairs.— In the higher forms the five somites which follow (and which might be termed the postoral somites) bear the true walking limbs (perciopoda, Spence Bate), the first pair of which in the Decapoda are usually developed into powerful chelae, and serve as the chief organs of prehension.

These podites are usually seven-jointed, and each bears a gill on its basal-joint. They are formed by the endopodite, the exopodite being present only in the larval-limb of the Decapoda; but in the adult Mysis (Stomapoda), eight pairs of limbs (that is to say, the five pairs of pereiopodites or “walking-feet,” and the three pairs of maxillipeds or “jaw-feet,”) are all furnished with two branches, one the endopodite, the other the exopodite, as in the larval Decapod.

Fifteenth to Twentieth pairs.— The next six somites bear each a pair of swimming-feet (or pleopodites). In the Decapoda-Brachyura these remain (like the segments on which they are borne) as extremely rudimentary organs furnished with hairs which serve for the protection of the eggs after extrusion. In the Macroura they assist in swimming, and are composed of a simple exopodite and endopodite. The sixth pair are developed into broad plates, forming the lateral lobes to the tail.

The Twenty first or caudal segment is destitute of appendages, and has therefore been considered by Prof. Huxley and others as a' “median appendage,” and not as a somite. It varies in form, being sometimes a broad flat plate in the Decapoda, or a minute terminal one in the Amphipoda, or greatly developed as a roof to the branchiae in some Isopoda, or forming a long terminal spine in the Xiphosura.

Internal Structure.—Nervous System. —The typical form of the nervous system in the young of all the Articulata is a chain of ganglions placed along the ventral surface of the body, and traversed in front by the gullet. This typical arrangement, however, undergoes great modifications in the several orders of Crustacea. Taking the Edriophthalmia, for example (fig. 7), we find the nervous system to consist of two parallel chords traversing the length of the body, each having its own ganglionic enlargement in each somite in juxtaposition, but not confluent; so that there is a distinct pair of ganglions for each segment. These are again united by transverse commissures, and each ganglionic knot gives off nervous filaments to the limbs of its particular somite.

In the lobster (Decapoda-Macrura), the nervous system consists of a longitudinally disposed series of differentsized ganglions connected together by commissural cords (fig. 8).

Primitively there is a pair of ganglions to each somite, but the three first pairs are fused together in the adult so as to form a large cerebral ganglion placed in front of the mouth, and called the supra-aesophageal ganglion. From this a nervous chord passes back on each side of the gullet to the large postoral ganglion, which is made up of six pairs of primitive ganglions fused together. Then follow five pairs of thoracic and six abdominal ganglions all distinct, but connected one with another by a nervous band formed of the primitive commissural chords which have coalesced along the middle line.

No solid internal skeleton separates this nervous axis from the alimentary system, though reflections of the external integument (apodemata) pass inwards, and more or less protect it. From this nervous axis all the nerves are given off, but none arise by two distinct roots like the spinal nerves of man.

In the prawn (Palaemon) and spiny lobster (Palinurus) the thoracic ganglia coalesce to form a long, elliptical, perforated nervous mass. In the hermit-crab (Pagurus) the cephalic ganglion presents a transversely quadrate form, sending off the usual nerves to the eyes, antennae, &c. The lateral oesophageal chords, after supplying the digestive system with the stomato gastric nerves, unite below to form the ganglion which distributes nerves to the maxillary apparatus and pharynx. This is succeeded by a large oblong ganglion situated at the base of the great nippers, and of the second pair of feet, both of which pairs it supplies. The lateral chords, diverging for the passage of the artery, re-unite to form a third thoracic ganglion, smaller than the second, supplying the third pair of thoracic feet, and sending off three pairs of nerves posteriorly. Of these the lateral pair goes to the fourth diminutive pair of feet; the median pair supplies the fifth pair of feet; the two remaining dorsal nerves, which are of minute size, form the continuations of the abdominal chords, and pass along the under or concave side of the soft, membranous, and highly sensitive abdomen to the anus, anterior to which the last small ganglion is situated; this supplies the nerves to the muscles of the caudal plates, here converted into claspers for enabling the animal to adhere to the columella of the spiral shell which it may have selected to protect the portion of its body undefended by the usual dense and insensible crustaceous covering (Owen).

The general progress of the development of the nervous system in the Crustacea has been, as we have seen, attended with increased size and diminished...

The Crustacea belong to the sub-kingdom Annulosa, and to the division Arthropoda, in which are also included the Insecta, the Myriapoda, and the Arachnida ; they are known also as Articulata, from the body being composed of a series of distinct rings or segments, each segment usually possessing a pair of jointed appendages or limbs articulated to it. They may be defined to be those Articulata which, whenever respiratory organs ⅛re specially developed, possess branchiae and not tracheae. By this definition they are at once separated from all insects and myriapods, which invariably possess tracheae. But it remains a difficulty, if it be not altogether impossible in the present state of science, to frame any definition which shall similarly include all Crustacea and exclude all Arachnida. In both classes, in fact, there are forms which possess no special respiratory organs; and if in these cases we resort to other characters, none which are of universal application have as yet been discovered.

It may be said, however, that as a rule these exceptional Crustacea possess more than four pairs of locomotive appendages, have two pairs of antennary organs, and possess a simple alimentary canal; while the Arachnida generally have not more than four pairs of locomotive appendages, possess at most one pair of antennary organs, and have their alimentary canal produced into caeca (Huxley).

External Structure. —The skin of the Crustacea is more or less completely hardened by a horny deposit called “chitine,” with or without the addition of lime, ] thus forming a defensive covering to the softer tissues of the animal. This hardened envelope serves also as an external skeleton, giving rigidity and support to the internal organs; and to its inflections, projections, and rugosities the muscles and membranes of the body and appendages are attached.

Body-Segments. —The crustacean exo-skeleton consists of a series of rings, usually a repetition of each other, and differing only in modification according to the necessity of the various portions of the animal. Each of these divisions is called a somite (Huxley).

The normal number of somites, or segments, is twenty-one; but instances occur among the extinct Trilobita and the recent Phyllopoda and Branchiopoda, in which a larger number of segments than twenty-one· are to be met with. On the other hand, many recent and fossil forms offer examples of Crustacea in which one or more segments are never developed; but this apparent absence is generally due to their coalescence, and we shall not unfr§quently find indications of this if we bear in mind the theory of Oken, that each pair of appendages indicates a separate segment. A knowledge, too, of the earlier (larval) stages of some of these forms has revealed the presence of the normal number of free segments in the young individual, which in later life are permanently soldered together.

Although the segments of tho Crustacea are greatly modified in the different orders, yet they can nevertheless be shown to be all composed of two lateral moieties resembling each other; we can also distinguish two arcs, the one superior, the other inferior, as shown in tho annexed figure (fig. 2).

The superior central pair united constitute the tergum (í, t), and the lateral are called the epimera (ep, ep).

The inferior arc is composed of the same number of pieces. The two median pieces unite to form the sternum (s, s), and the latero-inferiorpair are called the episternum (es, es). They are always united at the sternum; but there generally exists, between the inferior arc and the epimera situated above, a wide space destined for the articulation of the corresponding appendage (Milne-Edwards).

Mr C. Spence Bate, in his “Report on the British Edriophthalmia” (Brit. Assoc. Repts., 1855), differs from Milne-Edwards and other previous writers who had considered the series of scale-like plates at the sides of the body-segments of the Amphipoda as representing the “epimeral pieces” of each somite; on the contrary, he considers them to be the dilated coxal joint (or protopodite) of each limb. This view he adheres to in his chief work (1863, p. 3) on the sessile-eyed Crustacea, and reiterates in his Report (1875, p. 47), where he writes the epimera as sectional pieces in a theoretical construction of a somite cannot exist; they are really portions of the integument of the appendages. That they are present in the Amphipoda attached to the coxal joint of seven pairs of the limbs is readily seen; but in the Decapoda, Stomaρoda, and Isopoda it cannot by any means be so easily demonstrated. “We know of no example of a ring in which we are able to distinguish all the pieces that we desire to enumerate. In some there is an absence of certain pieces from the places they should occupy; sometimes they are very intimately soldered together, so that we cannot detect even a trace of separation; but in studying each of them separately, where it is most distinct, we shall be able to form a clear idea, and recognize its character in spite of its union with its neighbouring pieces. Moreover, although this analysis of the ring may not be always practicable, it is none the less true that it facilitates much the study of the exterior skeleton of articulated animals, and that it will permit us often to establish analogies where the greatest difference would at first sight appear to exist” (Milne-Edwards).

Professor Huxley in his lectures has somewhat simplified Milne-Edwards’s view of the crustacean segment. Taking for his type one of the body rings, or somites, of the common lobster (fig. 3), he points out that it consists of a convex upper part, called the tergum (∕), and a flatter inferior side, the sternum (s), the angle of junction on each side of the tergum and sternum being produced downwards, forming what is termed the pleuron (or epimer α) (y>Z.) For ordinary studies this view of a somite will be found sufficiently clear and simple.

From the inner surface of these tegumentary rings in the Crustacea various plates are given off which project into the internal cavity, constituting in some instances cells and canals.

According to Milne-Edwards, these processes are always developed at the points of union of two rings or of two neighbouring pieces of the same segment; and this disposition has obtained for them the name of apodema (fig. 4). They are the result of a fold of the integumentary membrane which penetrates more or less deeply between the organs, and which is strengthened with calcareous matter like the rest of the external structure, and always formed of two thin plates soldered together. They serve the office fulfilled by the bones in the Vertebrata, viz., that of affording solid surfaces to which the muscles are attached.

Divisions of the Body in the Crustacea.— By general consent and usage the body of a crustacean is divided into three regions, namely, head (or cephalon), thorax, and abdomen (see figs. 1 and 6), to each of which divisions seven out of the twenty-one segments are attributed. These terms are used as a matter of convenience, and are not assumed to be homologous with the grand divisions of head, thorax·, and abdomen, in the Vertebrata. All writers agree in considering the last seven segments to be abdominal. The only difference of opinion is as to the division of the first fourteen,—how many are cephalic and how many thoracic.

Dr Dana is of opinion that Crustacea have no distinct head, but only a cephalothorax composed of the fourteen anterior segments, yet he admits that in the Edriophthalmia the seven most anterior pairs of appendages are devoted to the mouth and organs of sensation, and in the extinct Pterygotus and in the Trilobita a distinct head certainly exists.

Professor Huxley considers that the division in the Podophthalmia is indicated by the cervical fold and by the sudder change in the character of the appendages between the sixth and seventh somites, and an equally marked similarity between the latter and those of the eighth and ninth pair. So that according to this view we should have six cephalic, eight thoracic, and six abdominal somites (for Professor Huxley regards the telson as not being a true somite but a median appendage, like the post-oral plate in Pterygotus). But, as Dana well observes, the mouth organs may become legs, or the legs may become mouth organs by slight variations, therefore this line of division can hardly be maintained on the character of the appendages alone, seeing it does not hold good for other groups equally entitled to consideration, as is the Podophthalmia.

The subjoined table may serve to show these several views more clearly :—

Arrangement and Nomenclature of the Somites or Bodyrings of the Crustacea, with their Appendages. [table]

The Appendages. —Just as we find a typical number of twenty-one body srgments to prevail among the Crustacea, so also in the appendages the type number of joints is seven, any departure from which is disguised by fusion of one or more joints together, the obsolete condition of others, or the depauperization of the limb into numerous articuli (see fig. õ). At the coxal joint, or protopodite, each limb usually bifurcates; firstly, there arises the external limb proper, or exopodite, which is normally seven-jointed; and secondly, the internal branch, or endopodite, which may serve as a mouth organ, a branchial appendix, a swimming organ, or a protection for the ova or the young. The appendages belonging to the three divisions of the body differ from each other in a greater or less degree in proportion to the higher or lower grade which we examine. Thus among the Decapoda (crabs and lobsters) the cephalic, thoracic, and abdominal somites all possess appendages with well marked characters, each series being highly differentiated for the functions to be performed by it. Among the Entomostraca, the appendages of the anterior cephalic somites alone are highly specialized, the others being either mere vegetative repetitions of one another, or else altogether wanting.

First pair.— The first cephalic somite supports the eyes, the most constant of all the organs, and probably the only pair of appendages which are never diverted from their normal use, though sometimes atrophied. In the more highly cephalized forms, the Decapoda-Brachyura (crabs), the eyes are placed on the outer s i de of the two pairs of antennae, but the anatomical evidence shows that the most anterior pair of nerves, in this as in all other orders of Crustacea, is that which is connected with the ophthalmic organs.

Second pair.— The second somite bears the first pair of antennae (or ardennules), called the inner pair in the higher forms, and the upper pair among the lower Crustacea. Ordinarily they are slender, tapering, freely-moving, multi-articulate organs. In the lobster both the endopodite and exopodite are equally developed from a common basal-joint or protopodite (see 2 in fig. 6).

Third pair.— The third somite supports the second or posterior pair of antennae, sometimes called the outer pair in the higher, and the inferior pair in the lower forms of Crustacea. In the lobster these are represented by a basal-joint or protopodite, and a long filamentary, multi-segmented endopodite, to the outer base of which a small scale is attached representing the exopodite. In all the higher Crustacea the three most anterior somites are always praeoral, being in front of the buccal orifice, and in most genera, moreover, they are specially set apart as bearing the organs of sense. Generally they are so closely blended together, both in the earlier stages of development and also in the adult forms, as to defy separation, the presence of three somites being only demonstrable by dissection, and by a knowledge of the fact that each pair of appendages, wherever it exists, presupposes a segment or ring to which it belongs. The genus Squilla affords, perhaps, the best evidence of the separate existence of these cephalic rings. In it the first, or ophthalmic somite, is quite distinct from the second and third antennary, which are also separable from one another, although the latter blends with the next somite, and the succeeding ones can only be distinguished by dissection. Usually the antennae or feelers are constant appendages; but still, the number and disposition of these organs varies extremely. Some of the lowest forms are wholly without antennae, or are furnished with them in a merely rudimentary state. Some species have only a single pair, the normal number, however, as we have already pointed out, is two pairs. In position they are inserted on the superior or inferior surface of the head, according to the development of the somites composing the cephalon. Ordinarily they are slender flexible multiarticulate appendages, but even among the higher forms they are subject to extraordinary modifications; thus in the Scyllaridae, the external pair are developed into broad flat organs of natation, and probably also for burrowing. In Arcturus, an Isopod, they are the nursery for the young; in the Entomostraca they are usually natatory organs; in Pterygotus and Limulus they are chelate, serving, as in the Copepoda, as clasping organs for the male. In the last free condition of the Cirripedia and Rhizocephala they serve as the organs for attachment,—being converted into cement-ducts in the former, and into root-like organs of nutrition in the latter. The second pair of antennae and sometimes even the first pair become mouth organs in the Merostomata.

Fourth to Ninth pairs. Epistomial or Mouth Organs.— In the Decapoda the six succeeding pairs may be called mouth-organs or epistomial appendages, being all engaged in duties subservient to nutrition. The fourth somite bears the actual jaws or mandibles proper with their palpi, outside which lie two pairs of maxillae, followed by three pairs of maxillipeds or jaw-feet. In each successive somite, these organs become less highly specialized mouthorgans, and betray the fact that they are after all only simple feet modified. Thus in Squilla (a Stomapod) the eighth somite (first thoracic) bears a pair of robust claws, the terminal joint of which is furnished with long and sharp teeth, these forming the.principal organs of prehension; whilst the ninth somite bears a pair of ordinary feet like the two following pairs (see fig. 71).

In most of the Edriophthalmia the mouth-organs extend only to the seventh somite, the eighth and ninth being included with the ambulatory members.

In the Decapoda we can detect the more or less rudimentary endopodite and exopodite in the fifth pair of appendages, and in each succeeding pair to the ninth; the eighth and ninth pairs also bear a third organ called an epipodite, and a gill or branchial organ.

Tenth to Fourteenth Pairs.— In the higher forms the five somites which follow (and which might be termed the postoral somites) bear the true walking limbs (perciopoda, Spence Bate), the first pair of which in the Decapoda are usually developed into powerful chelae, and serve as the chief organs of prehension.

These podites are usually seven-jointed, and each bears a gill on its basal-joint. They are formed by the endopodite, the exopodite being present only in the larval-limb of the Decapoda; but in the adult Mysis (Stomapoda), eight pairs of limbs (that is to say, the five pairs of pereiopodites or “walking-feet,” and the three pairs of maxillipeds or “jaw-feet,”) are all furnished with two branches, one the endopodite, the other the exopodite, as in the larval Decapod.

Fifteenth to Twentieth pairs.— The next six somites bear each a pair of swimming-feet (or pleopodites). In the Decapoda-Brachyura these remain (like the segments on which they are borne) as extremely rudimentary organs furnished with hairs which serve for the protection of the eggs after extrusion. In the Macroura they assist in swimming, and are composed of a simple exopodite and endopodite. The sixth pair are developed into broad plates, forming the lateral lobes to the tail.

The Twenty first or caudal segment is destitute of appendages, and has therefore been considered by Prof. Huxley and others as a' “median appendage,” and not as a somite. It varies in form, being sometimes a broad flat plate in the Decapoda, or a minute terminal one in the Amphipoda, or greatly developed as a roof to the branchiae in some Isopoda, or forming a long terminal spine in the Xiphosura.

Internal Structure.—Nervous System. —The typical form of the nervous system in the young of all the Articulata is a chain of ganglions placed along the ventral surface of the body, and traversed in front by the gullet. This typical arrangement, however, undergoes great modifications in the several orders of Crustacea. Taking the Edriophthalmia, for example (fig. 7), we find the nervous system to consist of two parallel chords traversing the length of the body, each having its own ganglionic enlargement in each somite in juxtaposition, but not confluent; so that there is a distinct pair of ganglions for each segment. These are again united by transverse commissures, and each ganglionic knot gives off nervous filaments to the limbs of its particular somite.

In the lobster (Decapoda-Macrura), the nervous system consists of a longitudinally disposed series of differentsized ganglions connected together by commissural cords (fig. 8).

Primitively there is a pair of ganglions to each somite, but the three first pairs are fused together in the adult so as to form a large cerebral ganglion placed in front of the mouth, and called the supra-aesophageal ganglion. From this a nervous chord passes back on each side of the gullet to the large postoral ganglion, which is made up of six pairs of primitive ganglions fused together. Then follow five pairs of thoracic and six abdominal ganglions all distinct, but connected one with another by a nervous band formed of the primitive commissural chords which have coalesced along the middle line.

No solid internal skeleton separates this nervous axis from the alimentary system, though reflections of the external integument (apodemata) pass inwards, and more or less protect it. From this nervous axis all the nerves are given off, but none arise by two distinct roots like the spinal nerves of man.

In the prawn (Palaemon) and spiny lobster (Palinurus) the thoracic ganglia coalesce to form a long, elliptical, perforated nervous mass. In the hermit-crab (Pagurus) the cephalic ganglion presents a transversely quadrate form, sending off the usual nerves to the eyes, antennae, &c. The lateral oesophageal chords, after supplying the digestive system with the stomato gastric nerves, unite below to form the ganglion which distributes nerves to the maxillary apparatus and pharynx. This is succeeded by a large oblong ganglion situated at the base of the great nippers, and of the second pair of feet, both of which pairs it supplies. The lateral chords, diverging for the passage of the artery, re-unite to form a third thoracic ganglion, smaller than the second, supplying the third pair of thoracic feet, and sending off three pairs of nerves posteriorly. Of these the lateral pair goes to the fourth diminutive pair of feet; the median pair supplies the fifth pair of feet; the two remaining dorsal nerves, which are of minute size, form the continuations of the abdominal chords, and pass along the under or concave side of the soft, membranous, and highly sensitive abdomen to the anus, anterior to which the last small ganglion is situated; this supplies the nerves to the muscles of the caudal plates, here converted into claspers for enabling the animal to adhere to the columella of the spiral shell which it may have selected to protect the portion of its body undefended by the usual dense and insensible crustaceous covering (Owen).

The general progress of the development of the nervous system in the Crustacea has been, as we have seen, attended with increased size and diminished...

The Crustacea belong to the sub-kingdom Annulosa, and to the division Arthropoda, in which are also included the Insecta, the Myriapoda, and the Arachnida ; they are known also as Articulata, from the body being composed of a series of distinct rings or segments, each segment usually possessing a pair of jointed appendages or limbs articulated to it. They may be defined to be those Articulata which, whenever respiratory organs ⅛re specially developed, possess branchiae and not tracheae. By this definition they are at once separated from all insects and myriapods, which invariably possess tracheae. But it remains a difficulty, if it be not altogether impossible in the present state of science, to frame any definition which shall similarly include all Crustacea and exclude all Arachnida. In both classes, in fact, there are forms which possess no special respiratory organs; and if in these cases we resort to other characters, none which are of universal application have as yet been discovered.

It may be said, however, that as a rule these exceptional Crustacea possess more than four pairs of locomotive appendages, have two pairs of antennary organs, and possess a simple alimentary canal; while the Arachnida generally have not more than four pairs of locomotive appendages, possess at most one pair of antennary organs, and have their alimentary canal produced into caeca (Huxley).

External Structure. —The skin of the Crustacea is more or less completely hardened by a horny deposit called “chitine,” with or without the addition of lime, ] thus forming a defensive covering to the softer tissues of the animal. This hardened envelope serves also as an external skeleton, giving rigidity and support to the internal organs; and to its inflections, projections, and rugosities the muscles and membranes of the body and appendages are attached.

Body-Segments. —The crustacean exo-skeleton consists of a series of rings, usually a repetition of each other, and differing only in modification according to the necessity of the various portions of the animal. Each of these divisions is called a somite (Huxley).

The normal number of somites, or segments, is twenty-one; but instances occur among the extinct Trilobita and the recent Phyllopoda and Branchiopoda, in which a larger number of segments than twenty-one· are to be met with. On the other hand, many recent and fossil forms offer examples of Crustacea in which one or more segments are never developed; but this apparent absence is generally due to their coalescence, and we shall not unfr§quently find indications of this if we bear in mind the theory of Oken, that each pair of appendages indicates a separate segment. A knowledge, too, of the earlier (larval) stages of some of these forms has revealed the presence of the normal number of free segments in the young individual, which in later life are permanently soldered together.

Although the segments of tho Crustacea are greatly modified in the different orders, yet they can nevertheless be shown to be all composed of two lateral moieties resembling each other; we can also distinguish two arcs, the one superior, the other inferior, as shown in tho annexed figure (fig. 2).

The superior central pair united constitute the tergum (í, t), and the lateral are called the epimera (ep, ep).

The inferior arc is composed of the same number of pieces. The two median pieces unite to form the sternum (s, s), and the latero-inferiorpair are called the episternum (es, es). They are always united at the sternum; but there generally exists, between the inferior arc and the epimera situated above, a wide space destined for the articulation of the corresponding appendage (Milne-Edwards).

Mr C. Spence Bate, in his “Report on the British Edriophthalmia” (Brit. Assoc. Repts., 1855), differs from Milne-Edwards and other previous writers who had considered the series of scale-like plates at the sides of the body-segments of the Amphipoda as representing the “epimeral pieces” of each somite; on the contrary, he considers them to be the dilated coxal joint (or protopodite) of each limb. This view he adheres to in his chief work (1863, p. 3) on the sessile-eyed Crustacea, and reiterates in his Report (1875, p. 47), where he writes the epimera as sectional pieces in a theoretical construction of a somite cannot exist; they are really portions of the integument of the appendages. That they are present in the Amphipoda attached to the coxal joint of seven pairs of the limbs is readily seen; but in the Decapoda, Stomaρoda, and Isopoda it cannot by any means be so easily demonstrated. “We know of no example of a ring in which we are able to distinguish all the pieces that we desire to enumerate. In some there is an absence of certain pieces from the places they should occupy; sometimes they are very intimately soldered together, so that we cannot detect even a trace of separation; but in studying each of them separately, where it is most distinct, we shall be able to form a clear idea, and recognize its character in spite of its union with its neighbouring pieces. Moreover, although this analysis of the ring may not be always practicable, it is none the less true that it facilitates much the study of the exterior skeleton of articulated animals, and that it will permit us often to establish analogies where the greatest difference would at first sight appear to exist” (Milne-Edwards).

Professor Huxley in his lectures has somewhat simplified Milne-Edwards’s view of the crustacean segment. Taking for his type one of the body rings, or somites, of the common lobster (fig. 3), he points out that it consists of a convex upper part, called the tergum (∕), and a flatter inferior side, the sternum (s), the angle of junction on each side of the tergum and sternum being produced downwards, forming what is termed the pleuron (or epimer α) (y>Z.) For ordinary studies this view of a somite will be found sufficiently clear and simple.

From the inner surface of these tegumentary rings in the Crustacea various plates are given off which project into the internal cavity, constituting in some instances cells and canals.

According to Milne-Edwards, these processes are always developed at the points of union of two rings or of two neighbouring pieces of the same segment; and this disposition has obtained for them the name of apodema (fig. 4). They are the result of a fold of the integumentary membrane which penetrates more or less deeply between the organs, and which is strengthened with calcareous matter like the rest of the external structure, and always formed of two thin plates soldered together. They serve the office fulfilled by the bones in the Vertebrata, viz., that of affording solid surfaces to which the muscles are attached.

Divisions of the Body in the Crustacea.— By general consent and usage the body of a crustacean is divided into three regions, namely, head (or cephalon), thorax, and abdomen (see figs. 1 and 6), to each of which divisions seven out of the twenty-one segments are attributed. These terms are used as a matter of convenience, and are not assumed to be homologous with the grand divisions of head, thorax·, and abdomen, in the Vertebrata. All writers agree in considering the last seven segments to be abdominal. The only difference of opinion is as to the division of the first fourteen,—how many are cephalic and how many thoracic.

Dr Dana is of opinion that Crustacea have no distinct head, but only a cephalothorax composed of the fourteen anterior segments, yet he admits that in the Edriophthalmia the seven most anterior pairs of appendages are devoted to the mouth and organs of sensation, and in the extinct Pterygotus and in the Trilobita a distinct head certainly exists.

Professor Huxley considers that the division in the Podophthalmia is indicated by the cervical fold and by the sudder change in the character of the appendages between the sixth and seventh somites, and an equally marked similarity between the latter and those of the eighth and ninth pair. So that according to this view we should have six cephalic, eight thoracic, and six abdominal somites (for Professor Huxley regards the telson as not being a true somite but a median appendage, like the post-oral plate in Pterygotus). But, as Dana well observes, the mouth organs may become legs, or the legs may become mouth organs by slight variations, therefore this line of division can hardly be maintained on the character of the appendages alone, seeing it does not hold good for other groups equally entitled to consideration, as is the Podophthalmia.

The subjoined table may serve to show these several views more clearly :—

Arrangement and Nomenclature of the Somites or Bodyrings of the Crustacea, with their Appendages. [table]

The Appendages. —Just as we find a typical number of twenty-one body srgments to prevail among the Crustacea, so also in the appendages the type number of joints is seven, any departure from which is disguised by fusion of one or more joints together, the obsolete condition of others, or the depauperization of the limb into numerous articuli (see fig. õ). At the coxal joint, or protopodite, each limb usually bifurcates; firstly, there arises the external limb proper, or exopodite, which is normally seven-jointed; and secondly, the internal branch, or endopodite, which may serve as a mouth organ, a branchial appendix, a swimming organ, or a protection for the ova or the young. The appendages belonging to the three divisions of the body differ from each other in a greater or less degree in proportion to the higher or lower grade which we examine. Thus among the Decapoda (crabs and lobsters) the cephalic, thoracic, and abdominal somites all possess appendages with well marked characters, each series being highly differentiated for the functions to be performed by it. Among the Entomostraca, the appendages of the anterior cephalic somites alone are highly specialized, the others being either mere vegetative repetitions of one another, or else altogether wanting.

First pair.— The first cephalic somite supports the eyes, the most constant of all the organs, and probably the only pair of appendages which are never diverted from their normal use, though sometimes atrophied. In the more highly cephalized forms, the Decapoda-Brachyura (crabs), the eyes are placed on the outer s i de of the two pairs of antennae, but the anatomical evidence shows that the most anterior pair of nerves, in this as in all other orders of Crustacea, is that which is connected with the ophthalmic organs.

Second pair.— The second somite bears the first pair of antennae (or ardennules), called the inner pair in the higher forms, and the upper pair among the lower Crustacea. Ordinarily they are slender, tapering, freely-moving, multi-articulate organs. In the lobster both the endopodite and exopodite are equally developed from a common basal-joint or protopodite (see 2 in fig. 6).

Third pair.— The third somite supports the second or posterior pair of antennae, sometimes called the outer pair in the higher, and the inferior pair in the lower forms of Crustacea. In the lobster these are represented by a basal-joint or protopodite, and a long filamentary, multi-segmented endopodite, to the outer base of which a small scale is attached representing the exopodite. In all the higher Crustacea the three most anterior somites are always praeoral, being in front of the buccal orifice, and in most genera, moreover, they are specially set apart as bearing the organs of sense. Generally they are so closely blended together, both in the earlier stages of development and also in the adult forms, as to defy separation, the presence of three somites being only demonstrable by dissection, and by a knowledge of the fact that each pair of appendages, wherever it exists, presupposes a segment or ring to which it belongs. The genus Squilla affords, perhaps, the best evidence of the separate existence of these cephalic rings. In it the first, or ophthalmic somite, is quite distinct from the second and third antennary, which are also separable from one another, although the latter blends with the next somite, and the succeeding ones can only be distinguished by dissection. Usually the antennae or feelers are constant appendages; but still, the number and disposition of these organs varies extremely. Some of the lowest forms are wholly without antennae, or are furnished with them in a merely rudimentary state. Some species have only a single pair, the normal number, however, as we have already pointed out, is two pairs. In position they are inserted on the superior or inferior surface of the head, according to the development of the somites composing the cephalon. Ordinarily they are slender flexible multiarticulate appendages, but even among the higher forms they are subject to extraordinary modifications; thus in the Scyllaridae, the external pair are developed into broad flat organs of natation, and probably also for burrowing. In Arcturus, an Isopod, they are the nursery for the young; in the Entomostraca they are usually natatory organs; in Pterygotus and Limulus they are chelate, serving, as in the Copepoda, as clasping organs for the male. In the last free condition of the Cirripedia and Rhizocephala they serve as the organs for attachment,—being converted into cement-ducts in the former, and into root-like organs of nutrition in the latter. The second pair of antennae and sometimes even the first pair become mouth organs in the Merostomata.

Fourth to Ninth pairs. Epistomial or Mouth Organs.— In the Decapoda the six succeeding pairs may be called mouth-organs or epistomial appendages, being all engaged in duties subservient to nutrition. The fourth somite bears the actual jaws or mandibles proper with their palpi, outside which lie two pairs of maxillae, followed by three pairs of maxillipeds or jaw-feet. In each successive somite, these organs become less highly specialized mouthorgans, and betray the fact that they are after all only simple feet modified. Thus in Squilla (a Stomapod) the eighth somite (first thoracic) bears a pair of robust claws, the terminal joint of which is furnished with long and sharp teeth, these forming the.principal organs of prehension; whilst the ninth somite bears a pair of ordinary feet like the two following pairs (see fig. 71).

In most of the Edriophthalmia the mouth-organs extend only to the seventh somite, the eighth and ninth being included with the ambulatory members.

In the Decapoda we can detect the more or less rudimentary endopodite and exopodite in the fifth pair of appendages, and in each succeeding pair to the ninth; the eighth and ninth pairs also bear a third organ called an epipodite, and a gill or branchial organ.

Tenth to Fourteenth Pairs.— In the higher forms the five somites which follow (and which might be termed the postoral somites) bear the true walking limbs (perciopoda, Spence Bate), the first pair of which in the Decapoda are usually developed into powerful chelae, and serve as the chief organs of prehension.

These podites are usually seven-jointed, and each bears a gill on its basal-joint. They are formed by the endopodite, the exopodite being present only in the larval-limb of the Decapoda; but in the adult Mysis (Stomapoda), eight pairs of limbs (that is to say, the five pairs of pereiopodites or “walking-feet,” and the three pairs of maxillipeds or “jaw-feet,”) are all furnished with two branches, one the endopodite, the other the exopodite, as in the larval Decapod.

Fifteenth to Twentieth pairs.— The next six somites bear each a pair of swimming-feet (or pleopodites). In the Decapoda-Brachyura these remain (like the segments on which they are borne) as extremely rudimentary organs furnished with hairs which serve for the protection of the eggs after extrusion. In the Macroura they assist in swimming, and are composed of a simple exopodite and endopodite. The sixth pair are developed into broad plates, forming the lateral lobes to the tail.

The Twenty first or caudal segment is destitute of appendages, and has therefore been considered by Prof. Huxley and others as a' “median appendage,” and not as a somite. It varies in form, being sometimes a broad flat plate in the Decapoda, or a minute terminal one in the Amphipoda, or greatly developed as a roof to the branchiae in some Isopoda, or forming a long terminal spine in the Xiphosura.

Internal Structure.—Nervous System. —The typical form of the nervous system in the young of all the Articulata is a chain of ganglions placed along the ventral surface of the body, and traversed in front by the gullet. This typical arrangement, however, undergoes great modifications in the several orders of Crustacea. Taking the Edriophthalmia, for example (fig. 7), we find the nervous system to consist of two parallel chords traversing the length of the body, each having its own ganglionic enlargement in each somite in juxtaposition, but not confluent; so that there is a distinct pair of ganglions for each segment. These are again united by transverse commissures, and each ganglionic knot gives off nervous filaments to the limbs of its particular somite.

In the lobster (Decapoda-Macrura), the nervous system consists of a longitudinally disposed series of differentsized ganglions connected together by commissural cords (fig. 8).

Primitively there is a pair of ganglions to each somite, but the three first pairs are fused together in the adult so as to form a large cerebral ganglion placed in front of the mouth, and called the supra-aesophageal ganglion. From this a nervous chord passes back on each side of the gullet to the large postoral ganglion, which is made up of six pairs of primitive ganglions fused together. Then follow five pairs of thoracic and six abdominal ganglions all distinct, but connected one with another by a nervous band formed of the primitive commissural chords which have coalesced along the middle line.

No solid internal skeleton separates this nervous axis from the alimentary system, though reflections of the external integument (apodemata) pass inwards, and more or less protect it. From this nervous axis all the nerves are given off, but none arise by two distinct roots like the spinal nerves of man.

In the prawn (Palaemon) and spiny lobster (Palinurus) the thoracic ganglia coalesce to form a long, elliptical, perforated nervous mass. In the hermit-crab (Pagurus) the cephalic ganglion presents a transversely quadrate form, sending off the usual nerves to the eyes, antennae, &c. The lateral oesophageal chords, after supplying the digestive system with the stomato gastric nerves, unite below to form the ganglion which distributes nerves to the maxillary apparatus and pharynx. This is succeeded by a large oblong ganglion situated at the base of the great nippers, and of the second pair of feet, both of which pairs it supplies. The lateral chords, diverging for the passage of the artery, re-unite to form a third thoracic ganglion, smaller than the second, supplying the third pair of thoracic feet, and sending off three pairs of nerves posteriorly. Of these the lateral pair goes to the fourth diminutive pair of feet; the median pair supplies the fifth pair of feet; the two remaining dorsal nerves, which are of minute size, form the continuations of the abdominal chords, and pass along the under or concave side of the soft, membranous, and highly sensitive abdomen to the anus, anterior to which the last small ganglion is situated; this supplies the nerves to the muscles of the caudal plates, here converted into claspers for enabling the animal to adhere to the columella of the spiral shell which it may have selected to protect the portion of its body undefended by the usual dense and insensible crustaceous covering (Owen).

The general progress of the development of the nervous system in the Crustacea has been, as we have seen, attended with increased size and diminished...