Encyclopaedia Britannica, 11th Edition, "Apollodorus" to "Aral" (part 4)

ARABI PASHA (c. 1839- ), more correctly Ahmad ‛Arābī, to which in later years he added the epithet al-Misrī, “the Egyptian,” Egyptian soldier and revolutionary leader, was born in Lower Egypt in 1839 or 1840 of a fellah family. Having entered the army as a conscript he was made an officer by Said Pasha in 1862, and was employed in the transport department in the Abyssinian campaign of 1875 under Ismail Pasha. A charge of peculation, unproved, was made against him in connexion with this expedition and he was placed on half-pay. During this time he joined a secret society formed by Ali Rubi with the object of getting rid of Turkish officers from the Egyptian army. Arabi also attended lectures at the mosque El Azhar and acquired a reputation as an orator. In 1878 he was employed by Ismail in fomenting a disturbance against the ministry of Nubar, Rivers Wilson and de Blignières, and received in payment a wife from Ismail’s harem and the command of a regiment. This increased his influence with the secret society, which, under the feeble government of Tewfik Pasha and the Dual Control, began to agitate against Europeans. In all that followed Arabi was put forward as the leader of the discontented Egyptians; he was in reality little more than the mouthpiece and puppet of abler men such as Ali Rubi and Mahmud Sami. On the 1st of February 1881 Arabi and two other Egyptian colonels, summoned before a court-martial for acts of disobedience, were rescued by their soldiers, and the khedive was forced to dismiss his then minister of war in favour of Mahmud Sami. A military demonstration on the 8th of September 1881, led by Arabi, forced the khedive to increase the numbers and pay of the army, to substitute Sherif Pasha for Riaz Pasha as prime minister, and to convene an assembly of notables. Arabi became under-secretary for war at the beginning of 1882, but continued his intrigues. The assembly of notables claimed the right of voting the budget, and thus came into conflict with the foreign controllers who had been appointed to guard the interests of the bondholders in the management of the Egyptian finances. Sherif fell in February, Mahmud Sami became prime minister, and Arabi (created a pasha) minister of war. Arabi, after a brief fall from office, acquired a dictatorial power that alarmed the British government. British and French warships went to Alexandria at the beginning of June; on the 11th of that month rioting in that city led to the sacrifice of many European lives. Order could only be restored through the intervention of Arabi, who now adopted a more distinctly anti-European attitude. His arming of the forts at Alexandria was held to constitute a menace to the British fleet. On the refusal of France to co-operate, the British fleet bombarded the forts (11th July), and a British force, under Sir Garnet Wolseley, defeated Arabi on the 13th of September at Tel-el-Kebir. Arabi fled to Cairo where he surrendered, and was tried (3rd of December) for rebellion. In accordance with an understanding made with the British representative, Lord Dufferin, Arabi pleaded guilty, and sentence of death was immediately commuted to one of banishment for life to Ceylon. The same sentence was passed on Mahmud Sami and others. After Arabi’s exile had lasted for nearly twenty years, however, the khedive Abbas II. exercised his prerogative of mercy, and in May 1901 Arabi was permitted to return to Egypt. Arabi, as has been said, was rather the figurehead than the inspirer of the movement of 1881-1882; and was probably more honest, as he was certainly less intelligent, than those whose tool, in a large measure, he was. The movement which he represented in the eye of Europe, whatever the motives of its leaders, “was in its essence a genuine revolt against misgovernment,” and it was a dim recognition of this fact which led Arabi to style himself “the Egyptian.”

See Egypt: History; also the accounts of Arabi in Khedives and Pashas, by C.F. Moberly Bell (1884); and in Lord Cromer’s Modern Egypt (1908).

Lord Cromer in Egypt, No. 1, 1905, p. 2.

ARABISTAN (formerly Khuzistan), a province of Persia, bounded on the S. by the Persian Gulf, on the W. by Turkish territory, on the N. by Luristan and on the E. by the Bakhtiari district and Fars. It has its modern name, signifying “land of the Arabs,” from the Arabs who form the bulk of the population, and is subdivided into the districts of Muhamrah, Fellahiyeh (the old Dorak), Ram Hormuz (popularly known as Ramiz), Havizeh, Shushter and Dizful. It has a population of about 200,000 and pays a yearly revenue of about £30,000. The soil is very fertile, but since the dam over the Karun at Ahvaz was swept away and the numerous canals which diverted the waters of the river for irrigation became useless, a great part of the province is uncultivated, and most of the crops and produce depend for water on rainfall and wells. The climate is hot, and in the low-lying, swampy districts very unhealthy; the prevailing winds are north-west and south-east, the former hot and dry from the arid districts west of Mesopotamia, the latter bearing much moisture from the Persian Gulf and the Indian Ocean. The principal Arab tribes are the Kab (generally known as Chaab) and Beni Lam, the former mostly settled in towns and villages and by religion Shi’ites, the latter nomads and Sunnites. The staples of food are dates and fish in the south, elsewhere the produce of the herds and flocks and rice, wheat and barley. Other products are maize, cotton, silk and indigo, and the manufactures include carpets without pile, coarse woollens, cottons and silk nettings. Dyeing is extensively carried on in Dizful where most of the indigo is grown.

Khuzistan (meaning “the land of the Khuz”) was a part of the Biblical Elam, the classical Susiana, and appears in the great inscription of Darius as Uvaja.

ARABS, the name given to that branch of the Semitic race which from the earliest historic times inhabited the south-western portion of the Arabian peninsula. The name, to-day the collective term for the overwhelming majority of the surviving Semitic peoples, was originally restricted to the nomad tribes who ranged the north of the peninsula east of Palestine and the Syro-Arabian desert. In this narrow sense “Arab” is used in the Assyrian inscriptions, in the Old Testament and in the Minaean inscriptions. Before the Christian era it had come to include all the inhabitants of the peninsula. This, it is suggested, may have been due to the fact that the “Arabs” were the chief people near the Greek and Roman colonies in Syria and Mesopotamia. Classical writers use the term both in its local and general sense. The Arabs to-day occupy, besides Arabia, a part of Mesopotamia, the western shores of the Red Sea, the eastern coast of the Persian Gulf and the north of Africa. The finest type of the race is found in south Arabia among the Ariba Arabs, among the mountaineers of Hadramut and Yemen and among the Bedouin tribes roaming over the interior of central and northern Arabia. The Arabs of the coasts and those of Mesopotamia are hybrids, showing Turkish, Negroid and Hamitic crossings. The people of Syria and Palestine are hybrids of Arab, Phoenician and Jewish descent. The theory that early Arab settlements were made on the east coast of Africa as far as Sofala south of the Zambezi, is without foundation; the earliest Arab settlement on the east coast of Africa that can be proved is Magadoxo (Mukdishu) in the 10th century, and the ruined cities of Mashonaland, once supposed to be the remains of Arab settlements, are now known to be of medieval African origin. On the East African coast-lands Arab influence is still considerable. Traces of the Arab type are met with in Asia Minor, the Caucasus, western Persia and India, while the influence of the Arab language and civilization is found in Europe (Malta and Spain), China and Central Asia.

The Arabs are at once the most ancient as they in many ways are the purest surviving type of the true Semite. Certainly the inhabitants of Yemen are not, and in historic times never were, pure Semites. Somali and other elements, generally described under the collective racial name of Hamitic, are clearly traceable; but the inland Arabs still present the nearest approach to the primitive Semitic type. The origin of the Arab race can only be a matter of conjecture. From the remotest historic times it has been divided into two branches, which from their geographical position it is simplest to call the North Arabians and the South Arabians. Arabic and Jewish tradition trace the descent of the latter from Joktan (Arabic Kahtan) son of Heber, of the former from Ishmael. The South Arabians—the older branch—were settled in the south-western part of the peninsula centuries before the uprise of the Ishmaelites. These latter include not only Ishmael’s direct descendants through the twelve princes (Gen. xxv. 16), but the Edomites, Moabites, Ammonites, Midianites and other tribes. This ancient and undoubted division of the Arab race —roughly represented to-day by the universally adopted classification into Arabs proper and Bedouin Arabs (see Bedouins)-has caused much dispute among ethnologists. All authorities agree in declaring the race to be Semitic in the broadest ethnological signification of that term, but some thought they saw in this division of the race an indication of a dual origin. They asserted that the purer branch of the Arab family was represented by the sedentary Arabs who were of Hamitic (Biblical Cushite), i.e. African ancestry, and that the nomad Arabs were Arabs only by adoption, and were nearer akin to the true Semite as sons of Ishmael. Many arguments were adduced in support of this theory, (1) The unquestioned division in remote historic times of the Arab race, and the immemorial hostility between the two branches. (2) The concurrence of pre-Islamitic literature and records in representing the first settlement of the “pure” Arab as made in the extreme south-western part of the peninsula, near Aden. (3) The use of Himyar, “dusky” or “red” (suggesting African affinities), as the name sometimes for the ruling class, sometimes for the entire people. (4) The African affinities of the Himyaritic language. (5) The resemblance of the grammar of the Arabic now spoken by the “pure” Arabs, where it differs from that of the North, to the Abyssinian grammar. (6) The marked resemblance of the pre-Islamitic institutions of Yemen and its allied provinces-its monarchies, courts, armies and serfs—to the historical Africo-Egyptian type and even to modern Abyssinia. (7) The physique of the “pure” Arab, the shape and size of the head, the slenderness of the lower limbs, all suggesting an African rather than an Asiatic origin. (8) The habits of the people, viz. their sedentary rather than nomad occupations, their fondness for village life, for dancing, music and society, their cultivation of the soil, having more in common with African life than with that of the western Asiatic continent. (9) The extreme facility of marriage which exists in all classes of the southern Arabs with the African races, the fecundity of such unions and the slightness or even total absence of any caste feeling between the dusky “pure” Arab and the still darker African, pointing to a community of origin. And further arguments were found in the characteristics of the Bedouins, their pastoral and nomad tendencies; the peculiarities of their idiom allied to the Hebrew; their strong clan feeling, their continued resistance to anything like regal power or centralized organization.

Such, briefly, were the more important arguments; but latterly ethnologists are inclined to agree that there is little really to be said for the African ancestry theory and that the Arab race had its beginning in the deserts of south Arabia, that in short the true Arabs are aborigines.

Mahommedans call the centuries before the Prophet’s birth waqt-el jahilīya, “the time of ignorance,” but the fact is that the Arab world has in some respects never since reached so high a level as it had in those days which it suits Moslems to paint in dreary colours. Writing was a fine art and poetry flourished. Eloquence was an accomplishment all strove to acquire, and each year there were assemblies, lasting sometimes a month, which were devoted to contests of skill among the orators and poets, to listen to whose friendly rivalry tribesmen journeyed long distances. Last, that surest index of a people’s civilization—the treatment of women—contrasted very favourably with their position under the Koran. Women had rights and were respected. The veil and the harem system were unknown before Mahomet. According to Nöldeke the Nabataean inscriptions and coins show that women held a high social position in northern Arabia, owning large estates and trading independently. Polyandry and polygamy, it is true, were practised, but the right of divorce belonged to the woman as well as the man. Two kinds of marriage were celebrated. One was a purely personal contract, with no witnesses, the wife not leaving her home or passing under marital authority. The other was a formal marriage, the woman becoming subject to her husband by purchase or capture. Even captive women were not kept in slavery. Arabic wealth and culture had indeed thus early reached a stage which justified Professor Robertson Smith in writing, “In this period the name of Arab was associated to Western writers with ideas of effeminate indolence and peaceful opulence ... the golden age of Yemen.” But long before Mahomet’s time this early Arab predominance was at an end, possibly due in great measure to the loss of the caravan trade through the increase of shipping. The abandonment of great cities and the ruin of many tribes contributed to the apparent nationalization of the Arab peoples. Though the traditional jealousy and hostility of the two branches, the Yemenites and Maadites or Ishmaelites, remained, the Arab world had attained by the levelling process of common misfortune the superficial unity it presents to-day. The nation thus formed, never a nation in the strict sense of the word, was distinctively and thoroughly Semitic in character and language, and has remained unchanged to the present day. The sporadic brilliancy of the ancient Arab kingdoms gave place to a social and political lethargy, the continuation of which for many centuries made the uprise of Saracenic empires seem a miracle to a world ignorant of the Arab past. The Arab race up to Mahomet’s day had been in the main pagan. Monotheism, if it ever prevailed, early gave place to sun and star worship, or simple idolatry. Professor Robertson Smith suggests that totemism was the earliest form of Arabian idolatry, and that each tribe had its sacred animal. This he supports by the fact that some tribal names were derived from those of animals, and that animal-worship was not unknown in Arabia. What seems certain is that Arab religion was of a complex hybrid nature, not much to be wondered at when one remembers that Arabia was the asylum of many religious refugees, Zoroastrians, Jews, Christians. In the later pre-Islamitic times spirits, or jinns, as they were called, of which each tribe or family had its own, were worshipped, and there was but a vague idea of a Supreme Being. Images of the jinns to the number of 360, one for each day of the lunar year, were collected in the temple at Mecca, the chief seat of their worship. That worship was of a sanguinary nature. Human sacrifice was fairly frequent. Under the guise of religion female infanticide was a common practice. At Mecca the great object of worship was a plain black stone, and to it pilgrimages were made from every part of Arabia. This stone was so sacred to the Arabs that even Mahomet dared not dispense with it, and it remains the central object of sanctity in the Ka’ba to-day. The temples of the Sabaeans and the Minaeans were built east of their cities, a fact suggesting sun-worship, yet this is not believed to have been the cult of the Minaeans. Common to both was the worship of Attar, the male Ashtoreth.

With the appearance of Mahomet the Arabs took anew a place in the world’s history.

Physically the Arabs are one of the strongest and noblest races of the world. Baron de Larrey, surgeon-general to Napoleon on his expedition to Egypt and Syria, writes: “Their physical structure is in all respects more perfect than that of Europeans; their organs of sense exquisitely acute, their size above the average of men in general, their figure robust and elegant, their colour brown; their intelligence proportionate to their physical perfection and without doubt superior, other things being equal, to that of other nations.” The typical Arab face is of an oval form, lean-featured; the eyes a brilliant black, deep-set under bushy eyebrows; nose aquiline, forehead straight but not high. In body the Arab is muscular and long-limbed, but lean. Deformed individuals or dwarfs are rare among Arabs; nor, except leprosy, which is common, does any disease seem to be hereditary among them. They often suffer from ophthalmia, though not in the virulent Egyptian form. They are scrupulously clean in their persons, and take special care of their teeth, which are generally white and even. Simple and abstemious in their habits, they often reach an extreme yet healthy old age; nor is it common among them for the faculties of the mind to give way sooner than those of the body.

Thus, physically, they yield to few races, if any, of mankind; mentally, they surpass most, and are only kept back in the march of progress by the remarkable defect of organizing power and incapacity for combined action. Lax and imperfect as are their forms of government, it is with impatience that even these are borne; of the four caliphs who alone reigned—if reign theirs could be called—in Arabia proper, three died a violent death; and of the Wahhabi princes, the most genuine representatives in later times of pure Arab rule, almost all have met the same fate. The Arab face, which is not unkindly, but never smiling, expresses that dignity and gravity which are typical of the race. While the Arab is always polite, good-natured, manly and brave, he is also revengeful, cruel, untruthful and superstitious. Of the Arab nature Burckhardt (other authorities, e.g. Barth and Rohlfs, are far less complimentary) wrote: “The Arab displays his manly character when he defends his guest at the peril of his own life, and submits to the reverses of fortune, to disappointment and distress, with the most patient resignation. He is distinguished from a Turk by the virtues of pity and gratitude. The Turk is cruel, the Arab of a more kind temper; he pities and supports the wretched, and never forgets the generosity shown to him even by an enemy.” The Arab will lie and cheat and swear false oaths, but once his word is pledged he may be trusted to the last. There are some oaths such as Wallah (by Allah) which mean nothing, but such an oath as the threefold one with wa, bi and ta as particles of swearing the meanest thief will not break. In temper, or at least in the manifestation of it, the Arab is studiously calm; and he rarely so much as raises his voice in a dispute. But this outward tranquillity covers feelings alike keen and permanent; and the remembrance of a rash jest or injurious word, uttered years before, leads only too often to that blood-revenge which is a sacred duty everywhere in Arabia.

There exist, however, marked tribal or almost semi-national diversities of character among the Arabs. Thus, the inhabitants of Hejaz are noted for courtesy and blamed for fickleness; those of Nejd are distinguished by their stern tenacity and dignity of deportment; the nations of Yemen are gentle and pliant, but revengeful; those of Hasa and Oman cheerful and fond of sport, though at the same time turbulent and unsteady. Anything approaching to a game is rare in Nejd, and in the Hejaz religion and the yearly occurrence of the pilgrim ceremonies almost exclude all public diversions; but in Yemen the well-known game of the “jerid,” or palm-stick, with dances and music is not rare. In Oman such amusements are still more frequent. Again in Yemen and Oman, coffee-houses, where people resort for conversation, and where public recitals, songs and other amusements are indulged in, stand open all day; while nothing of the sort is tolerated in Nejd. So too the ceremonies of circumcision or marriage are occasions of gaiety and pastime on the coast, but not in the central provinces.

An Arab town, or even village, except it be the merest hamlet, is invariably walled round; but seldom is a stronger material than dried earth used; the walls are occasionally flanked by towers of like construction. A dry ditch often surrounds the whole. The streets are irregular and seldom parallel. The Arab, indeed, lacks an eye for the straight. The Arab carpenter cannot form a right angle; an Arab servant cannot place a cloth square on a table. The Ka’ba at Mecca has none of its sides or angles equal. The houses are of one or two storeys, rarely of three, with flat mud roofs, little windows and no external ornament. If the town be large, the expansion of one or two streets becomes a market-place, where are ranged a few shops of eatables, drugs, coffee, cottons or other goods. Many of these shops are kept by women. The chief mosque is always near the market-place; so is also the governor’s residence, which, except in size and in being more or less fortified Arab fashion, does not differ from a private house. Drainage is unthought of; but the extreme dryness of the air obviates the inconvenience and disease that under other skies could not fail to ensue, and which in the damper climates of the coast make themselves seriously felt. But the streets are roughly swept every day, each householder taking care of the roadway that lies before his own door. Whitewash and colour are occasionally used in Yemen, Hejaz and Oman; elsewhere a light ochre tint, the colour of the sun-dried bricks, predominates, and gives an Arab town the appearance at a distance of a large dust-heap in the centre of the bright green ring of gardens and palm-groves. Baked bricks are unknown in Arabia, and stone buildings are rare, especially in Nejd. Palm branches and the like, woven in wattles, form the dwellings, of the poorer classes in the southern districts. Many Arab towns possess watch-towers, like huge round factory chimneys in appearance, built of sun-dried bricks, and varying in height from 50 to 100 ft. or even more. Indeed, two of these constructions at the town of Birkat-el-Mauj, in Oman, are said to be each of 170 ft. in height, and that of Nezwah, in the same province, is reckoned at 140; but these are of stone.

The principal feature in the interior of an Arab house is the “kahwah” or coffee-room. It is a large apartment spread with mats, and sometimes furnished with carpets and a few cushions. At one end is a small furnace or fireplace for preparing coffee. In this room the men congregate; here guests are received, and even lodged; women rarely enter it, except at times when strangers are unlikely to be present. Some of these apartments are very spacious and supported by pillars; one wall is usually built transversely to the compass direction of the Ka’ba; it serves to facilitate the performance of prayer by those who may happen to be in the kahwah at the appointed times. The other rooms are ordinarily small.

The Arabs are proverbially hospitable. A stranger’s arrival is often the occasion of an amicable dispute among the wealthier inhabitants as to who shall have the privilege of receiving him. Arab cookery is of the simplest. Roughly-ground wheat cooked with butter; bread in thin cakes, prepared on a heated iron plate or against the walls of an open oven; a few vegetables, generally of the leguminous kinds; boiled mutton or camel’s flesh, among the wealthy; dates and fruits—this is the menu of an ordinary meal. Rice is eaten by the rich and fish is common on the coasts. Tea, introduced only a few decades back, is now largely drunk. A food of which the Arabs are fond is locusts boiled in salt and water and then dried in the sun. They taste like stale shrimps, but there is a great sale for them. Spices are freely employed; butter much too largely for a European taste.

After eating, the hands are always washed, soap or the ashes of an alkaline plant being used. A covered censer with burning incense is then passed round, and each guest perfumes his hands, face, and sometimes his clothes; this censer serves also on first receptions and whenever special honour is intended. In Yemen and Oman scented water often does duty for it. Coffee, without milk or sugar, but flavoured with an aromatic seed brought from India, is served to all. This, too, is done on the occasion of a first welcome, when the cups often make two or three successive rounds; but, in fact, coffee is made and drunk at any time, as frequently as the desire for it may suggest itself; and each time fresh grains are sifted, roasted, pounded and boiled—a very laborious process, and one that requires in the better sort of establishments a special servant or slave for the work. Arabs generally make but one solid meal a day—that of supper, soon after sunset. Even then they do not eat much, gluttony being rare among them, and even daintiness esteemed disgraceful. Wine, like other fermented drinks, is prohibited by the Koran, and is, in fact, very rarely taken, though the inhabitants of the mountains of Oman are said to indulge in it. On the coast spirits of the worst quality are sometimes procured; opium and hashish are sparingly indulged in. On the other hand, wherever Wahhābiism has left freedom of action, tobacco-smoking prevails; short pipes of clay, long pipes with large open bowls, or most frequently the water-pipe or “nar-ghileh,” being used. The tobacco smoked is generally strong and is either brought from the neighbourhood of Bagdad or grown in the country itself. The strongest quality is that of Oman; the leaf is broad and coarse, and retains its green colour even when dried; a few whiffs have been known to produce absolute stupor. The aversion of the Wahhābis to tobacco is well known; they entitle it “mukhzi” or “the shameful,” and its use is punished with blows, as the public use of wine would be elsewhere.

In dress much variety prevails. The loose cotton drawers girded at the waist, which in hot climates do duty for trousers, are not often worn, even by the upper classes, in Nejd or Yemama, where a kind of silk dressing-gown is thrown over the long shirt; frequently, too, a brown or black cloak distinguishes the wealthier citizen; his head-dress is a handkerchief fastened round the head by a band. But in Hejaz, Yemen and Oman, turbans are by no means uncommon; the ordinary colour is white; they are worn over one or more skullcaps. Trousers also form part of the dress in the two former of these districts; and a voluminous sash, in which a dagger or an inkstand is stuck, is wrapped round the waist. The poorer folk, however, and the villagers often content themselves with a broad piece of cloth round the loins, and another across the shoulders. In Oman trousers are rare, but over the shirt a long gown, of peculiar and somewhat close-fitting cut, dyed yellow, is often worn. The women in these provinces commonly put on loose drawers and some add veils to their head-dresses; they are over-fond of ornaments (gold and silver); their hair is generally arranged in a long plait hanging down behind. All men allow their beards and moustaches full growth, though this is usually scanty. Most Arabs shave their heads, and indeed all, strictly speaking, ought by Mahommedan custom to do so. An Arab seldom or never dyes his hair. Sandals are worn more often than shoes; none but the very poorest go barefoot.

Slavery is still, as of old times, a recognized institution throughout Arabia; and an illicit traffic in blacks is carried on along the coasts of the Persian Gulf and the Red Sea. The slaves themselves were obtained chiefly from the east African coast districts down as far as Zanzibar, but this source of supply was practically closed by the end of the 19th century. Slaves are usually employed in Arabia as herdsmen or as domestic servants, rarely in agricultural work; they also form a considerable portion of the bodyguards with which Eastern greatness loves to surround itself. Like their countrymen elsewhere, they readily embrace the religion of their masters and become zealous Mahommedans. Arab custom enfranchises a slave who has accepted Islam at the end of seven years of bondage, and when that period has arrived, the master, instead of exacting from his slave the price of freedom, generally, on giving him his liberty, adds the requisite means for supporting himself and a family in comfort. Further, on every important occasion, such as a birth, circumcision, a marriage or a death, one or more of the household slaves are sure of acquiring their freedom. Hence Arabia has a considerable free black population; and these again, by inter-marriage with the whites around, have filled the land with a mulatto breed of every shade, till, in the eastern and southern provinces especially, a white skin is almost an exception. In Arabia no prejudice exists against negro alliances; no social or political line separates the African from the Arab. A negro may become a sheik, a kadi, an amir, or whatever his industry and his talents may render him capable of being. This is particularly so in Nejd, Yemen and Hadramut; in the Hejaz and the north a faint line of demarcation may be observed between the races.

The Arabs are good soldiers but poor generals. Personal courage, wonderful endurance of privation, fixity of purpose, and a contempt of death are qualities common to almost every race, tribe and clan that compose the Arab nation. In skirmishing and harassing they have few equals, while at close quarters they have often shown themselves capable of maintaining, armed with swords and spears alone, a desperate struggle against guns and bayonets, neither giving nor receiving quarter. Nor are they wholly ignorant of tactics, their armies, when engaged in regular war, being divided into centre and wings, with skirmishers in front and a reserve behind, often screened at the outset of the engagement by the camels of the expedition. These animals, kneeling and ranged in long parallel rows, form a sort of entrenchment, from behind which the soldiers of the main body fire their matchlocks, while the front divisions, opening out, act on either flank of the enemy. This arrangement of troops may be traced in Arab records as far back as the 5th century, and was often exemplified during the Wahhābi wars.

Arab women are scarcely less distinguished for their bravery than the men. Records of armed heroines occur frequently in the chronicles or myths of the pre-Islamitic time; and in authentic history the Battle of the Camel, 656 A.D., where Ayesha, the wife of Mahomet, headed the charge, is only the first of a number of instances in which Arab amazons have taken, sword in hand, no inconsiderable share in the wars and victories of Islam. Even now it is the custom for an Arab force to be always accompanied by some courageous maiden, who, mounted on a blackened camel, leads the onslaught, singing verses of encouragement for her own, of insult for the opposing tribe. Round her litter the fiercest of the battle rages, and her capture or death is the signal of utter rout; it is hers also to head the triumph after the victory of her clan.

There is little education, in the European sense of the word, in Arabia. Among the Bedouins there are no schools, and few, even of the most elementary character, in the towns or villages. Where they exist, little beyond the mechanical reading of the Koran, and the equally mechanical learning of it by rote, is taught. On the other hand, Arab male-children, brought up from early years among the grown-up men of the house or tent, learn more from their own parents and at home than is common in other countries; reading and writing are in most instances thus acquired, or rather transmitted; besides such general principles of grammar and eloquence, often of poetry and history, as the elders themselves may be able to impart. To this family schooling too are due the good manners, politeness, and self-restraint that early distinguish Arab children. In the very few instances where a public school of a higher class exists, writing, grammar and rhetoric sum up its teachings. Law and theology, in the narrow sense that both these words have in the Islamitic system, are explained in afternoon lectures given in most mosques; and some verses of the Koran, with one of the accepted commentaries, that of Baidawi for example, form the basis of the instruction. Great attention is paid to accuracy of grammar and purity of diction throughout Arabia; yet something of a dialectic difference may be observed in the various districts. The purest Arabic, that which is as nearly as possible identical in the choice of words and in its inflections with the language of the Koran, is spoken in Nejd, and the best again of that in the province of Suder. Next in purity comes the Arabic of Shammar. Throughout the Hejaz in general, the language, though extremely elegant, is not equally correct; in el-Hasa, Bahrein and Oman it is decidedly influenced by the foreign element called Nabataean. In Yemen, as in other southern districts of the peninsula, Arabic merges insensibly into the Himyaritic or African dialect of Hadramut and Mahra. (See Semitic Languages.)

Bibliography.—Lieutenant Wellsted, Travels in Arabia (Lond., 1838); “Narrative of a Journey to the Ruins of Nakeb el Hajar” (Jour. R. Geog. Soc. vii. 20); Carsten Niebuhr. Travels through Arabia (transl. into English by Robert Heron, 2 vols., Edin., 1792); John Lewis Burckhardt, Travels in Arabia (2 vols., Lond., 1829); Notes on the Bedouins and Wahabis, (2 vols., Lond., 1830; in German, Weimar, 1831); C.J. Cruttenden, Journal of an Excursion to Sana’a, the Capital of Yemen (Bombay, 1838); A. Sprenger, Die alte Geographie Arabiens als Grundlage der Entwicklungsgeschichte des Semitismus (Berne, 1875); Sir Richard F. Burton, Personal Narrative of a Pilgrimage to El Medinah and Meccah (Lond., 1855); W. Robertson Smith, Kinship and Marriage in Early Arabia (Cambridge); E. Reclus, Les Arabes (Brussels, 1898); Lady Anne Blunt, A Pilgrimage to Nejd (2 vols., Lond., 1881); C.M. Doughty, Arabia Deserta (2 vols., 1888); Rev. S.M. Zwemer, Arabia: the Cradle of Islam (1900); Albrecht Zehme, Arabien und die Araber, seit hundert Jahren (1875).

ARACAJÚ, a city and seaport of Brazil, capital of the state of Sergipe, 170 m. N.N.E. of Bahia, on the river Cotinguiba, or Cotindiba, 6 m. from the coast. The municipality, of which it forms a part, had a population in 1890 of 16,336, about two-thirds of whom lived in the city itself. Aracajú is a badly built town on the right bank of the river at the base of a ridge of low sand-hills and has the usual features of an unprogressive provincial capital. Good limestone is quarried in its vicinity, and the country tributary to this port produces large quantities of sugar. Cotton is also grown, and the back country sends down hides and skins for shipment. The anchorage is good, but a dangerous bar at the mouth of the river prevents the entrance of vessels drawing more than 12 ft. The port is visited, therefore, only by the smaller steamers of the coastwise lines. The river is navigable as far as the town of Maroim, about 10 m. beyond Aracajú. The city was founded in 1855.

ARACATY, or Aracatí, a city and port of Brazil, in the state of Ceará, 75 m. S.E. of Fortaleza, on the river Jaguaribe, 8 m. from the sea. Pop. of the municipality (1890) 20,182, of whom about 12,000 belonged to the city. A dangerous bar at the mouth of the river permits the entrance only of the smaller coasting steamers, but the port is an important commercial centre, and exports considerable quantities of cotton, hides, maniçoba, rubber, fruit, and palm wax.

ARACHNE, in Greek mythology, the daughter of Idmon of Colophon in Lydia, a dyer in purple. She had acquired such skill in the art of weaving that she ventured to challenge Athena. While the goddess took as subjects her quarrel with Poseidon as to the naming and possession of Attica, and the warning examples of those who ventured to pit themselves against the immortals, Arachne depicted the metamorphoses of the gods and their amorous adventures. Her work was so perfect that Athena, enraged at being unable to find any blemish in it, tore it to pieces. Arachne hanged herself in despair; but the goddess out of pity loosened the rope, which became a cobweb, while Arachne herself was changed into a spider (Ovid, Metam. vi. 5-145). The story probably indicates the superiority of Asia over Greece in the textile arts.

ARACHNIDA, the zoological name given in 1815 by Lamarck (Gr. ἁράχνη, a spider) to a class which he instituted for the reception of the spiders, scorpions and mites, previously classified by Linnaeus in the order Aptera of his great group Insecta. Lamarck at the same time founded the class Crustacea for the lobsters, crabs and water-fleas, also until then included in the order Aptera of Linnaeus. Lamarck included the Thysanura and the Myriapoda in his class Arachnida. The Insecta of Linnaeus was a group exactly equivalent to the Arthropoda founded a hundred years later by Siebold and Stannius. It was thus reduced by Lamarck in area, and made to comprise only the six-legged, wing-bearing “Insecta.” For these Lamarck proposed the name Hexapoda; but that name has been little used, and they have retained to this day the title of the much larger Linnaean group, viz. Insecta. The position of the Arachnida in the great sub-phylum Arthropoda, according to recent anatomical and embryological researches, is explained in the article Arthropoda. The Arachnida form a distinct class or line of descent in the grade Euarthropoda, diverging (perhaps in common at the start with the Crustacea) from primitive Euarthropods, which gave rise also to the separate lines of descent known as the classes Diplopoda, Crustacea, Chilopoda and Hexapoda.

LAP, Left anterior process.

RAP, Right anterior process.

PhN, Pharyngeal notch.

ALR, Anterior lateial rod or tendon.

PLR, Posterior lateral rod or tendon.

PLP, Posterior lateral process.

Natural size.

(From Lankester, Q. J. Mic. Sci., N S vol. xxiv, 1884.)

Limulus an Arachnid.—Modern views as to the classification and affinities of the Arachnida have been determined by the demonstration that Limulus and the extinct Eurypterines (Pterygotus, &c.) are Arachnida; that is to say, are identical in the structure and relation of so many important parts with Scorpio, whilst differing in those respects from other Arthropoda, that it is impossible to suppose that the identity is due to homoplasy or convergence, and the conclusion must be accepted that the resemblances arise from close genetic relationship. The view that Limulus, the king-crab, is an Arachnid was maintained as long ago as 1829 by Strauss-Dürckheim (1), on the ground of its possession of an internal cartilaginous sternum—also possessed by the Arachnida (see figs. 1, 2, 3, 4, 5 and 6)—and of the similarity of the disposition of the six leg-like appendages around the mouth in the two cases (see figs. 45 and 63). The evidence of the exact equivalence of the segmentation and appendages of Limulus and Scorpio, and of a number of remarkable points of agreement in structure, was furnished by Ray Lankester in an article published in 1881 (“Limulus an Arachnid,” Quart. Journ. Micr. Sci. vol. xxi. N.S.), and in a series of subsequent memoirs, in which the structure of the entosternum, of the coxal glands, of the eyes, of the veno-pericardiac muscles, of the respiratory lamellae, and of other parts, was for the first time described, and in which the new facts discovered were shown uniformly to support the hypothesis that Limulus is an Arachnid. A list of these memoirs is given at the close of this article (2, 3, 4, 5 and 13). The Eurypterines (Gigantostraca) were included in the identification, although at that time they were supposed to possess only five pairs of anterior or prosomatic appendages. They have now been shown to possess six pairs (fig. 47), as do Limulus and Scorpio.

Fig. 2.—Ventral surface of the entosternum of Limulus polyphemus, Latr. Letters as in fig. 1 with the addition of NF, neural fossa protecting the aggregated ganglia of the central nervous system; PVP, left posterior ventral process; PMP, posterior median process. Natural size.

(From Lankester.)

Fig. 3.—Entosternum of scorpion (Palamnaeus Indus, de Geer); dorsal surface.

asp, Paired anterior process of the sub-neural arch.

snp, Sub-neural arch.

ap, Anterior lateral process (same as RAP and LAP in fig. 1).

lmp, Lateral median process (same as ALR and PLR of fig. 1).

pp, Posterior process (same as PLP in fig. 1).

pf, Posterior flap or diaphragm of Newport.

m1 and m2, Perforations of the diaphragm for the passage of muscles.

DR, The paired dorsal ridges.

GC, Gastric canal or foramen.

AC, Arterial canal or foramen.

(After Lankester, loc. cit.)

The various comparisons previously made between the structure of Limulus and the Eurypterines on the one hand, and that of a typical Arachnid, such as Scorpio, on the other, had been vitiated by erroneous notions as to the origin of the nerves supplying the anterior appendages of Limulus (which were finally removed by Alphonse Milne-Edwards in his beautiful memoir (6) on the structure of that animal), and secondly by the erroneous identification of the double sternal plates of Limulus, called “chilaria,” by Owen, with a pair of appendages (7). Once the identity of the chilaria with the pentagonal sternal plate of the scorpion is recognized—an identification first insisted on by Lankester—the whole series of segments and appendages in the two animals, Limulus and Scorpio, are seen to correspond most closely, segment for segment, with one another (see figs. 7 and 8). The structure of the prosomatic appendages or legs is also seen to present many significant points of agreement (see figures), but a curious discrepancy existed in the six-jointed structure of the limb in Limulus, which differed from the seven-jointed limb of Scorpio by the defect of one joint. R.I. Pocock of the British Museum has observed that in Limulus a marking exists on the fourth joint, which apparently indicates a previous division of this segment into two, and thus establishes the agreement of Limulus and Scorpio in this small feature of the number of segments in the legs (see fig. 11).

It is not desirable to occupy the limited space of this article by a full description of the limbs and segments of Limulus and Scorpio. The reader is referred to the complete series of figures here given, with their explanatory legends (figs 12, 13, 14, 15). Certain matters, however, require comment and explanation to render the comparison intelligible. The tergites, or chitinized dorsal halves of the body rings, are fused to form a “prosomatic carapace,” or carapace of the prosoma, in both Limulus and Scorpio (see figs. 7 and 8). This region corresponds in both cases to six somites, as indicated by the presence of six pairs of limbs. On the surface of the carapace there are in both animals a pair of central eyes with simple lens and a pair of lateral eye-tracts, which in Limulus consist of closely-aggregated simple eyes, forming a “compound” eye, whilst in Scorpio they present several separate small eyes. The microscopic structure of the central and the lateral eyes has been shown by Lankester and A.G. Bourne (5) to differ; but the lateral eyes of Scorpio were shown by them to be similar in structure to the lateral eyes of Limulus, and the central eyes of Scorpio to be identical in structure with the central eyes of Limulus (see below).

Fig. 4.—Ventral surface of the same entosternum as that drawn in fig. 3. Letters as in fig. 3 with the addition of NC, neural canal or foramen.

(After Lankester, loc. cit.)

Fig. 5.—Entosternum of one of the mygalomorphous spiders; ventral surface. Ph.N., pharyngeal notch. The posterior median process with its repetition of triangular segments closely resembles the same process in Limulus.

(From Lankester, loc. cit.)

Fig. 6.—Dorsal surface of the same entosternum as that drawn in fig. 5. Ph.N., pharyngeal notch.

After Lankester, loc. cit.

Following the prosoma is a region consisting of six segments (figs. 14 and 15), each carrying a pair of plate-like appendages in both Limulus and Scorpio. This region is called the mesosoma. The tergites of this region and those of the following region, the metasoma, are fused to form a second or posterior carapace in Limulus, whilst remaining free in Scorpio. The first pair of foliaceous appendages in each animal is the genital operculum; beneath it are found the openings of the genital ducts. The second pair of mesosomatic appendages in Scorpio are known as the “pectens.” Each consists of an axis, bearing numerous blunt tooth-like processes arranged in a series. This is represented in Limulus by the first gill-bearing appendage. The leaves (some 150 in number) of the gill-book (see figure) correspond to the tooth-like processes of the pectens of Scorpio. The next four pairs of appendages (completing the mesosomatic series of six) consist, in both Scorpio and Limulus, of a base carrying each 130 to 150 blood-holding, leaf-like plates, lying on one another like the leaves of a book. Their minute structure is closely similar in the two cases; the leaf-like plates receive blood from the great sternal sinus, and serve as respiratory organs. The difference between the gill-books of Limulus and the lung-books of Scorpio depends on the fact that the latter are adapted to aerial respiration, while the former serve for aquatic respiration. The appendage carrying the gill-book stands out on the surface of the body in Limulus, and has other portions developed besides the gill-book and its base; it is fused with its fellow of the opposite side. On the other hand, in Scorpio, the gill-book-bearing appendage has sunk below the surface, forming a recess or chamber for itself, which communicates with the exterior by an oval or circular “stigma” (fig. 10, stg). That this in-sinking has taken place, and that the lung-books or in-sunken gill-books of Scorpio really represent appendages (that is to say, limbs or parapodia) is proved by their developmental history (see figs. 17 and 18). They appear at first as outstanding processes on the surface of the body.

The exact mode in which the in-sinking of superficial outstanding limbs, carrying gill-lamellae, has historically taken place has been a matter of much speculation. It was to be hoped that the specimen of the Silurian scorpion (Palaeophonus) from Scotland, showing the ventral surface of the mesosoma (fig. 49), would throw light on this matter; but the specimen recently carefully studied by the writer and Pocock reveals neither gill-bearing limbs nor stigmata. The probability appears to be against an actual introversion of the appendage and its lamellae, as was at one time suggested by Lankester. It is probable that such an in-sinking as is shown in the accompanying diagram has taken place (fig. 15); but we are yet in need of evidence as to the exact equivalence of margins, axis, &c., obtaining between the lung-book of Scorpio and the gill-book of Limulus. Zoologists are familiar with many instances (fishes, crustaceans) in which the protective walls of a water-breathing organ or gill-apparatus become converted into an air-breathing organ or lung, but there is no other case known of the conversion of gill processes themselves into air-breathing plates.

oc, Lateral compound eyes.

oc′, Central monomeniscous eyes.

PA, Post-anal spine.

I to VI, The six appendage-bearing somites of the prosoma.

VII, Usually considered to be the tergum of the genital somite, but suggested by Pocock to be that of the otherwise suppressed praegenital somite.

VIII to XIII, The six somites of the mesosoma, each with a movable pleural spine and a pair of dorsal entopophysis or muscle-attaching ingrowths.

XIV to XVIII, The confluent or unexpressed six somites of the metasoma.

[According to the system of numbering explained in the text, if VII is the tergum of the praegenital somite (as is probable) it should be labelled Prg without any number, and the somites VIII to XIII should be lettered 1 to 6, indicating that they are the six normal somites of the mesosoma; whilst XV to XVIII should be replaced by the numbers 7 to 12—an additional suppressed segment (making up the typical six) being reckoned to the metasomatic fusion.]

(From Lankester, Q.J. Micr Set. vol. xxi., 1881.)

Fig. 8.—Diagram of the dorsal surface of a scorpion to compare with fig. 7. Letters and Roman numerals as in fig. 7, excepting that VII is here certainly the tergum of the first somite of the mesosoma—the genital somite—and is not a survival of the embryonic praegenital somite. The anus (not seen) is on the sternal surface.

(From Lankester, loc. cit.)

The identification of the lung-books of Scorpio with the gill-books of Limulus is practically settled by the existence of the pectens in Scorpio (fig. 14, VIII) on the second mesosomatic somite. There is no doubt that these are parapodial or limb appendages, carrying numerous imbricated secondary processes, and therefore comparable in essential structure to the leaf-bearing plates of the second mesosomatic somite of Limulus. They have remained unenclosed and projecting on the surface of the body, as once were the appendages of the four following somites. But they have lost their respiratory function. In non-aquatic life such an unprotected organ cannot subserve respiration. The “pectens” have become more firmly chitinized and probably somewhat altered in shape as compared with their condition in the aquatic ancestral scorpions. Their present function in scorpions is not ascertained. They are not specially sensitive under ordinary conditions, and may be touched or even pinched without causing any discomfort to the scorpion. It is probable that they acquire special sensibility at the breeding season and serve as “guides” in copulation. The shape of the legs and the absence of paired terminal claws in the Silurian Palaeophonus (see figs. 48 and 49) as compared with living scorpions (see fig. 10) show that the early scorpions were aquatic, and we may hope some day in better-preserved specimens than the two as yet discovered, to find the respiratory organs of those creatures in the condition of projecting appendages serving aquatic respiration somewhat as in Limulus, though not necessarily repeating the exact form of the broad plates of Limulus.

It is important to note that the series of lamellae of the lung-book and the gill-book correspond exactly in structure, the narrow, flat blood-space in the lamellae being interrupted by pillar-like junctions of the two surfaces in both cases (see Lankester (4)), and the free surfaces of the adjacent lamellae being covered with a very delicate chitinous cuticle which is drawn out into delicate hairs and processes. The elongated axis which opens at the stigma in Scorpio and which can be cleared of soft, surrounding tissues and coagulated blood so as to present the appearance of a limb axis carrying the book-like leaves of the lung is not really, as it would seem to be at first sight, the limb axis. That is necessarily a blood-holding structure and is obliterated and fused with soft tissues of the sternal region so that the lamellae cannot be detached and presented as standing out from it. The apparent axis or basal support of the scorpion’s lung-books shown in the figures, is a false or secondary axis and merely a part of the infolded surface which forms the air-chamber. The maceration of the soft parts of a scorpion preserved in weak spirit and the cleaning of the chitinized in-grown cuticle give rise to the false appearance of a limb axis carrying the lamellae. The margins of the lamellae of the scorpion’s lung-book, which are lowermost in the figures (fig. 15) and appear to be free, are really those which are attached to the blood-holding axis. The true free ends are those nearest the stigma.

Passing on now from the mesosoma we come in Scorpio to the metasoma of six segments, the first of which is broad whilst the rest are cylindrical. The last is perforated by the anus and carries the post-anal spine or sting. The somites of the metasoma carry no parapodia. In Limulus the metasoma is practically suppressed. In the allied extinct Eurypterines it is well developed, and resembles that of Scorpio. In the embryo Limulus (fig. 42) the six somites of the mesosoma are not fused to form a carapace at an early stage, and they are followed by three separately marked metasomatic somites; the other three somites of the metasoma have disappeared in Limulus, but are represented by the unsegmented prae-anal region. It is probable that we have in the metasoma of Limulus a case of the disappearance of once clearly demarcated somites. It would be possible to suppose, on the other hand, that new somites are only beginning to make their appearance here. The balance of various considerations is against the latter hypothesis. Following the metasoma in Limulus, we have as in Scorpio the post-anal spine—in this case not a sting, but a powerful and important organ of locomotion, serving to turn the animal over when it has fallen upon its back. The nature of the post-anal spine has been strangely misinterpreted by some writers. Owen (7) maintained that it represented a number of coalesced somites, regardless of its post-anal position and mode of development. The agreement of the grouping of the somites, of the form of the parapodia (appendages, limbs) in each region, of the position of the genital aperture and operculum, of the position and character of the eyes, and of the powerful post-anal spines not seen in other Arthropods, is very convincing as to the affinity of Limulus and Scorpio. Perhaps the most important general agreement of Scorpio compared with Limulus and the Eurypterines is the division of the body into the three regions (or tagmata)—prosoma, mesosoma and metasoma—each consisting of six segments, the prosoma having leg-like appendages, the mesosoma having foliaceous appendages, and the metasoma being destitute of appendages.

Fig. 9.—Ventral view of the posterior carapace or meso-metasomatic (opisthospmatic) fusion of Limulus polyphemus. The soft integument and limbs of the mesosoma have been removed as well as all the viscera and muscles, so that the inner surface of the terga of these somites with their entopophyses are seen. The unsegmented dense chitinous sternal plate of the metasoma (XIII to XVIII) is not removed. Letters as in fig. 7.

After Lankester, loc. cit.)

Fig. 10.—Ventral view of a scorpion, Palamnaeus indus, de Geer, to show the arrangement of the coxae of the limbs, the sternal elements, genital plate and pectens.

M, Mouth behind the oval median camerostome.

I, The chelicerae.

II, The chelae.

III to VI, the four pairs of walking legs.

VIIgo, The genital somite or first somite of the mesosoma with the genital operculum (a fused pair of limbs).

VIIIp, The pectiniferous somite.

IXstg to XIIstg, the four pulmonary somites.

met, The pentagonal metasternite of the prosoma behind all the coxae.

x, The sternum of the pectiniferous somite.

y, The broad first somite of the metasoma.

Fig. 11.—Third leg of Limulus polyphemus, showing the division of the fourth segment of the leg by a groove S into two, thus giving seven segments to the leg as in scorpion.

(From a drawing by Pocock.)

In 1893, some years after the identification of the somites of Limulus with those of Scorpio, thus indicated, had been published, zoologists were startled by the discovery by a Japanese zoologist, Kishinouye (8), of a seventh prosomatic somite in the embryo of Limulus longispina. This was seen in longitudinal sections, as shown in fig. 19. The simple identification of somite with somite in Limulus and Scorpio seemed to be threatened by this discovery. But in 1896 Dr August Brauer of Marburg (9) discovered in the embryo of Scorpio a seventh prosomatic somite (see VII PrG, figs. 17 and 18), or, if we please so to term it, a praegenital somite, hitherto unrecognized. In the case of Scorpio this segment is indicated in the embryo by the presence of a pair of rudimentary appendages, carried by a well-marked somite. As in Limulus, so in Scorpio, this unexpected somite and its appendages disappear in the course of development. In fact, more or less complete “excalation” of the somite takes place. Owing to its position it is convenient to term the somite which is excalated in Limulus and Scorpio “the praegenital somite.” It appears not improbable that the sternal plates wedged in between the last pair of legs in both Scorpio and Limulus, viz. the pentagonal sternite of Scorpio (fig. 10) and the chilaria of Limulus (see figs. 13 and 20), may in part represent in the adult the sternum of the excalated praegenital somite. This has not been demonstrated by an actual following out of the development, but the position of these pieces and the fact that they are (in Limulus) supplied by an independent segmental nerve, favours the view that they may comprise the sternal area of the vanished praegenital somite. This interpretation, however, of the “metasternites” of Limulus and Scorpio is opposed by the coexistence in Thelyphonus (figs. 55, 57 and 58) of a similar metasternite with a complete praegenital somite. H.J. Hansen (10) has recognized that the “praegenital somite” persists in a rudimentary condition, forming a “waist” to the series of somites in the Pedipalpi and Araneae. The present writer is of opinion that it will be found most convenient to treat this evanescent somite as something special, and not to attempt to reckon it to either the prosoma or the mesosoma. These will then remain as typically composed each of six appendage-bearing somites-the prosoma comprising in addition the ocular prosthomere. When the praegenital somite or traces of it are present it should not be called “the seventh prosomatic” or the “first mesosomatic,” but simply the “praegenital somite.” The first segment of the mesosoma of Scorpio and Limulus thus remains the first segment, and can be identified as such throughout the Eu-arachnida, carrying as it always does the genital apertures. But it is necessary to remember, in the light of recent discoveries, that the sixth prosomatic pair of appendages is carried on the seventh somite of the whole series, there being two prosthomeres or somites in front of the mouth, the first carrying the eyes, the second the chelicerae; also that the first mesosomatic or genital somite is not the seventh or even the eighth of the whole senes of somites which have been historically present, but is the ninth, owing to the presence or to the excalation of a praegenital somite. It seems that confusion and trouble will be best avoided by abstaining from the introduction of the non-evident somites, the ocular and the praegenital, into the numerical nomenclature of the component somites of the three great body regions. We shall, therefore, ignoring the ocular somite, speak of the first, second, third, fourth, fifth and sixth leg-bearing somites of the prosoma, and indicate the appendages by the Roman numerals, I, II, III, IV, V, VI, and whilst ignoring the praegenital somite we shall speak of the first, second, third, &c., somite of the mesosoma or opisthosoma (united mesosoma and metasoma) and indicate them by the Arabic numerals.

There are a number of other important points of structure besides those referring to the somites and appendages in which Limulus agrees with Scorpio or other Arachnida and differs from other Arthropoda. The chief of these are as follows:—

1. The Composition of the Head (that is to say, of the anterior part of the prosoma) with especial Reference to the Region in Front of the Mouth.—It appears (see Arthropoda) that there is embryological evidence of the existence of two somites in Arachnida which were originally post-oral, but have become prae-oral by adaptational shifting of the oral aperture. These forwardly-slipped somites are called “prosthomeres.” The first of these has, in Arachnids as in other Arthropods, its pair of appendages represented by the eyes. The second has for its pair of appendages the small pair of limbs which in all living Arachnids is either chelate or retrovert (as in spiders), and is known as the chelicerae. It is possible, as maintained by some writers (Patten and others), that the lobes of the cerebral nervous mass in Arachnids indicate a larger number of prosthomeres as having fused in this region, but there is no embryological evidence at present which justifies us in assuming the existence in Arachnids of more than two prosthomeres. The position of the chelicerae of Limulus and of the ganglionic nerve-masses from which they receive their nerve-supply, is closely similar to that of the same structures in Scorpio. The cerebral mass is in Limulus more easily separated by dissection as a median lobe distinct from the laterally-placed ganglia of the chelceral somite than is the case in Scorpio, but the relations are practically the same in the two forms. Formerly it was supposed that in Limulus both the chelicerae and the next following pair of appendages were prosthomerous, as in Crustacea, but the dissections of Alphonse Milne-Edwards (6) demonstrated the true limitations of the cerebrum, whilst embryological researches have done as much for Scorpio. Limulus thus agrees with Scorpio and differs from the Crustacea, in which there are three prosthomeres—one ocular and two carrying palpiform appendages. It is true that in the lower Crustacea (Apus, &c.) we have evidence of the gradual movement forward of the nerve-ganglia belonging to these palpiform appendages. But although in such lower Crustacea the nerve-ganglia of the third prosthomere have not fused with the anterior nerve-mass, there is no question as to the prae-oral position of two appendage-bearing somites in addition to the ocular prosthomere. The Crustacea have, in fact, three prosthomeres in the head and the Arachnida only two, and Limulus agrees with the Arachnida in this respect and differs from the Crustacea. The central nervous systems of Limulus and of Scorpio present closer agreement in structure than can be found when a Crustacean is compared with either. The wide divarication of the lateral cords in the prosoma and their connexion by transverse commissures, together with the “attraction” of ganglia to the prosomatic ganglion group which properly belong to hinder segments, are very nearly identical in the two animals. The form and disposition of the ganglion cells are also peculiar and closely similar in the two. (See Patten (42) for important observations on the neuromeres, &c., of Limulus and Scorpio.)

Fig. 12.—The prosomatic appendages of Limulus polyphemus (right) and Scorpio (left), Palamnaeus indus compared. The corresponding appendages are marked with the same Roman numeral. The Arabic numerals indicate the segments of the legs.

cox, Coxa or basal segment of the leg.

stc, The sterno-coxal process or jaw-like up-growth of the coxa.

epc, The articulated movable outgrowth of the coxa, called the epi-coxite (present only in III of the scorpion and III, IV and V of Limulus).

ex1, The exopodite of the sixth limb of Limulus.

a, b, c, d, Movable processes on the same leg (see for some suggestions on the morphology of this leg, Pocock in Quart. Journ. Micr. Sci. March 1901; see also fig. 50 below and explanation).

(From Lankester, loc. cit.)

Fig. 13.—Diagrams of the metasternite st, with genital operculum op, and the first lamelligerous pair of appendages ga, with uniting sternal element st of Scorpio (left) and Limulus (right).

(From Lankester, loc. cit.)

2. The Minute Structure of the Central Eyes and of the Lateral Eyes.—Limulus agrees with Scorpio not only in having a pair of central eyes and also lateral eyes, but in the microscopic structure of those organs, which differs in the central and lateral eyes respectively. The central eyes are “simple eyes,” that is to say, have a single lens, and are hence called “monomeniscous.” The lateral eyes are in Limulus “compound eyes,” that is to say, consist of many lenses placed close together; beneath each lens is a complex of protoplasmic cells, in which the optic nerve terminates. Each such unit is termed an “ommatidium.” The lateral eyes of Scorpio consist of groups of separate small lenses each with its ommatidium, but they do not form a continuous compound eye as in Limulus. The ommatidium (soft structure beneath the lens-unit of a compound eye) is very simple in both Scorpio and Limulus. It consists of a single layer of cells, continuous with those which secrete the general chitinous covering of the prosoma. The cells of the ommatidium are a good deal larger than the neighbouring common cells of the epidermis. They secrete the knob-like lens (fig. 22). But they also receive the nerve fibres of the optic nerve. They are at the same time both optic nerve-end cells, that is to say, retina cells, and corneagen cells or secretors of the chitinous lens-like cornea. In Limulus (fig. 23) each ommatidium has a peculiar ganglion cell developed in a central position, whilst the ommatidium of the lateral eyelets of Scorpio shows small intermediate cells between the larger nerve-end cells. The structure of the lateral eye of Limulus was first described by Grenacher, and further and more accurately by Lankester and Bourne (5) and by Watase; that of Scorpio by Lankester and Bourne, who showed that the statements of von Graber were erroneous, and that the lateral eyes of Scorpio have a single cell-layered or “monostichous” ommatidium like that of Limulus. Watase has shown, in a very convincing way, how by deepening the pit-like set of cells beneath a simple lens the more complex ommatidia of the compound eyes of Crustacea and Hexapoda may be derived from such a condition as that presented in the lateral eyes of Limulus and Scorpio. (For details the reader is referred to Watase (11) and to Lankester and Bourne (5).) The structure of the central eyes of Scorpio and spiders and also of Limulus differs essentially from that of the lateral eyes in having two layers of cells (hence called diplostichous) beneath the lens, separated from one another by a membrane (figs. 24 and 25). The upper layer is the corneagen and secretes the lens, the lower is the retinal layer. The mass of soft cell-structures beneath a large lens of a central eye is called an “ommatoeum.” It shows in Scorpio and Limulus a tendency to segregate into minor groups or “ommatidia.” It is found that in embryological growth the retinal layer of the central eyes forms as a separate pouch, which is pushed in laterally beneath the corneagen layer from the epidermic cell layer. Hence it is in origin double, and consists of a true retinal layer and a post-retinal layer (fig. 24, B), though these are not separated by a membrane. Accordingly the diplostichous ommatoeum or soft tissue of the Arachnid’s central eye should strictly be called “triplostichous,” since the deep layer is itself doubled or folded. The retinal cells of both the lateral and central eyes of Limulus and Scorpio produce cuticular structures on their sides; each such piece is a rhabdomere and a number (five or ten) uniting form a rhabdom (fig. 26). In the specialized ommatidia of the compound eyes of Crustacea and Hexapods the rhabdom is an important structure. It is a very significant fact that the lateral and central eyes of Limulus and Scorpio not only agree each with each in regard to their monostichous and diplostichous structure, but also in the formation in both classes of eyes of rhabdomeres and rhabdoms in which the component pieces are five or a multiple of five (fig. 26). Whilst each unit of the lateral eye of Limulus has a rhabdom of ten pieces forming a star-like chitinous centre in section, each lateral eye of Scorpio has several rhabdoms of five or less rhabdomeres, indicating that the Limulus lateral eye-unit is more specialized than the detached lateral eyelet of Scorpio, so as to present a coincidence of one lens with one rhabdom. Numerous rhabdomeres (grouped as rhabdoms in Limulus) are found in the retinal layer of the central eyes also.

VII, The genital operculum.

VIII, The pectens of Scorpio and the first branchial plate of Limulus.

IX, The first pair of lung-books of Scorpio and the second branchial plate of Limulus.

gp, Genital pore.

epst, Epistigmatic sclerite.

stg, Stigma or orifice of the hollow tendons of the branchial plates of Limulus.

(After Lankester, loc. cit.)

Whilst Limulus agrees thus closely with Scorpio in regard to the eyes, it is to be noted that no Crustacean has structures corresponding to the peculiar diplostichous central eyes, though these occur again (with differences in detail) in Hexapoda. Possibly, however, an investigation of the development of the median eyes of some Crustacea (Apus, Palaemon) may prove them to be diplostichous in origin.

3. The so-called “Coxal Glands.”—In 1882 (Proc. Roy. Soc. No. 221) Lankester described under the name “coxal glands” a pair of brilliantly white oviform bodies lying in the Scorpion’s prosoma immediately above the coxae of the fifth and sixth pairs of legs (fig. 27). These bodies had been erroneously supposed by Newport (12) and other observers to be glandular outgrowths of the alimentary canal. They are really excretory glands, and communicate with the exterior by a very minute aperture on the posterior face of the coxa of the fifth limb on each side. When examined with the microscope, by means of the usual section method, they are seen to consist of a labyrinthine tube lined with peculiar cells, each cell having a deep vertically striated border on the surface farthest from the lumen, as is seen in the cells of some renal organs. The coils and branches of the tube are packed by connective tissue and blood spaces. A similar pair of coxal glands, lobate instead of ovoid in shape, was described by Lankester in Mygale, and it was also shown by him that the structures in Limulus called “brick-red glands” by Packard have the same structure and position as the coxal glands of Scorpio and Mygale. In Limulus these organs consist each of four horizontal lobes lying on the coxal margin of the second, third, fourth, and fifth prosomatic limbs, the four lobes being connected to one another by a transverse piece or stem (fig. 28). Microscopically their structure is the same in essentials as that of the coxal glands of Scorpio (13). Coxal glands have since been recognized and described in other Arachnida. In 1900 it was shown that the coxal gland of Limulus is provided with a very delicate thin-walled coiled duct which opens, even in the adult condition, by a minute pore on the coxa of the fifth leg (Patten and Hazen, 13A). Previously to this, Lankester’s pupil Gulland had shown (1885) that in the embryo the coxal gland is a comparatively simple tube, which opens to the exterior in this position and by its other extremity into a coelomic space. Similar observations were made by Laurie (17) in Lankester’s laboratory (1890) with regard to the early condition of the coxal gland of Scorpio, and by Bertkau (41) as to that of the spider Atypus. H.M. Bernard (13B) showed that the opening remains in the adult scorpion. In all the embryonic or permanent opening is on the coxa of the fifth pair of prosomatic limbs. Thus an organ newly discovered in Scorpio was found to have its counterpart in Limulus.

The name “coxal gland” needs to be carefully distinguished from “crural gland,” with which it is apt to be confused. The crural glands, which occur in many terrestrial Arthropods, are epidermal in origin and totally distinct from the coxal glands. The coxal glands of the Arachnida are structures of the same nature as the green glands of the higher Crustacea and the so-called “shell glands” of the Entomostraca. The latter open at the base of the fifth pair of limbs of the Crustacean, just as the coxal glands open on the coxal joint of the fifth pair of limbs of the Arachnid. Both belong to the category of “coelomoducts,” namely, tubular or funnel-like portions of the coelom opening to the exterior in pairs in each somite (potentially,) and usually persisting in only a few somites as either “urocoels” (renal organs) or “gonocoets” (genital tubes). In Peripatus they occur in every somite of the body. They have till recently been very generally identified with the nephridia of Chaetopod worms, but there is good reason for considering the true nephridia (typified by the nephridia of the earthworm) as a distinct class of organs (see Lankester in vol. ii. chap. in. of A Treatise on Zoology, 1900). The genital ducts of Arthropoda are, like the green glands, shell glands and coxal glands, to be regarded as coelomoducts (gonocoels). The coxal glands do not establish any special connexion between Limulus and Scorpio, since they also occur in the same somite in the lower Crustacea, but it is to be noted that the coxal glands of Limulus are in minute structure and probably in function more like those of Arachnids than those of Crustacea.

Fig. 15.—The remaining three pairs of mesosomatic appendages of Scorpio and Limulus. Letters as in fig. 14. l130 indicates that there are 130 lamellae in the scorpion’s lung-book, whilst l150 indicates that 150 similar lamellae are counted in the gill of Limulus.

(After Lankester, loc. cit.)

4. The Entosternites and their Minute Structure.—Strauss-Dürckheim (1) was the first to insist on the affinity between Limulus and the Arachnids, indicated by the presence of a free suspended entosternum or plastron or entosternite in both. We have figured here (figs. 1 to 6) the entosternites of Limulus, Scorpio and Mygale. Lankester some years ago made a special study of the histology (3) of these entosternites for the purpose of comparison, and also ascertained the relations of the very numerous muscles which are inserted into them (4). The entosternites are cartilaginous in texture, but they have neither the chemical character nor the microscopic structure of the hyaline cartilage of Vertebrates. They yield chitin in place of chondrin or gelatin—as does also the cartilage of the Cephalopod’s endoskeleton. In microscopic structure they all present the closest agreement with one another. We find a firm, homogeneous or sparsely fibrillated matrix in which are embedded nucleated cells (corpuscles of protoplasm) arranged in rows of three, six or eight, parallel with the adjacent lines of fibrillation.

Fig. 16.—Diagram to show the way in which an outgrowing gill-process bearing blood-holding lamellae, may give rise, if the sternal body wall sinks inwards, to a lung-chamber with air-holding lamellae.

I is the embryonic condition.

bs, Blood sinus.

L is the condition of outgrowth with gl, gill lamellae.

A is the condition of in-sinking of the sternal surface and consequent enclosure of the lamelligerous surface of the appendage in a chamber with narrow orifice—the pulmonary air-holding chamber.

pl, Pulmonary lamellae.

bs, Blood sinus.

(After Kingsley.)

Fig. 17.—Embryo of scorpion, ventral view showing somites and appendages.

sgc, Frontal groove.

sa, Rudiment of lateral eyes.

obl, Camerostome (upper lip).

so, Sense-organ of Patten.

PrGabp1, Rudiment of the appendage of the praegenital somite which disappears.

abp2, Rudiment of the right half of the genital operculum.

abp3, Rudiment of the right pecten.

abp4 to abp7. Rudiments of the four appendages which carry the pulmonary lamellae.

I to VI, Rudiments of the six limbs of the prosoma.

VIIPrG, The evanescent praegenital somite.

VIII, The first mesosomatic somite or genital somite.

IX, The second mesosomatic somite or pectiniferous somite.

X to XIII, The four pulmoniferous somites.

XIV, The first metasomatic somite.

(After Brauer, Zeitsch. wiss. Zool., vol. lix., 1895.)

A minute entosternite having the above-described structure is found in the Crustacean Apus between the bases of the mandibles, and also in the Decapoda in a similar position, but in no Crustacean does it attain to any size or importance. On the other hand, the entosternite of the Arachnida is a very large and important feature in the structure of the prosoma, and must play an important part in the economy of these organisms. In Limulus (figs. 1 and 2) it has as many as twenty-five pairs of muscles attached to it, coming to it from the bases of the surrounding limbs and from the dorsal carapace and from the pharynx. It consists of an oblong plate 2 in. in length and 1 in breadth, with a pair of tendinous outgrowths standing out from it at right angles on each side. It “floats” between the prosomatic nerve centres and the alimentary canal. In each somite of the mesosoma is a small, free entosternite having a similar position, but below or ventral to the nerve cords, and having a smaller number of muscles attached to it. The entosternite was probably in origin part of the fibrous connective tissue lying close to the integument of the sternal surface—giving attachment to muscles corresponding more or less to those at present attached to it. It became isolated and detached, why or with what advantage to the organism it is difficult to say, and at that period of Arachnidan development the great ventral nerve cords occupied a more lateral position than they do at present. We know that such a lateral position of the nerve cords preceded the median position in both Arthropoda and Chaetopoda. Subsequently to the floating off of the entosternite the approximation of the nerve cords took place in the prosoma, and thus they were able to take up a position below the entosternite. In the mesosoma the approximation had occurred before the entosternites were formed.

Fig. 18.—Portion of a similar embryo at a later stage of growth. The praegenital somite, VII PrG, is still present, but has lost its rudimentary appendages; go, the genital operculum, left half; Km, the left pecten; abp4 to abp7, the rudimentary appendages of the lung-sacs.

(After Brauer, loc. cit.)

Fig. 19.—Section through an early embryo of Limulus longispina, showing seven transverse divisions in the region of the unsegmented anterior carapace. The seventh, VII, is anterior to the genital operculum, op, and is the cavity of the praegenital somite which is more or less completely suppressed in subsequent development, possibly indicated by the area marked VII in fig. 7 and by the great entopophyses of the prosomatic carapace.

(After Kishinouye, Journ. Sci. Coll. Japan, vol. v., 1892.)

In the scorpion (figs. 3 and 4) the entosternite has tough membrane-like outgrowths which connect it with the body-wall, both dorsally and ventrally forming an oblique diaphragm, cutting off the cavity of the prosoma from that of the mesosoma. It was described by Newport as “the diaphragm.” Only the central and horizontal parts of this structure correspond precisely to the entosternite of Limulus: the right and left anterior processes (marked ap in figs. 3 and 4, and RAP, LAP, in figs. 1 and 2) correspond in the two animals, and the median lateral process lmp of the scorpion represents the tendinous outgrowths ALR, PLR of Limulus. The scorpion’s entosternite gives rise to outgrowths, besides the great posterior flaps, pf, which form the diaphragm, unrepresented in Limulus. These are a ventral arch forming a neural canal through which the great nerve cords pass (figs. 3 and 4, snp), and further a dorsal gastric canal and arterial canal which transmit the alimentary tract and the dorsal artery respectively (figs. 3 and 4, GC, DR).

In Limulus small entosternites are found in each somite of the appendage-bearing mesosoma, and we find in Scorpio, in the only somite of the mesosoma which has a well-developed pair of appendages, that of the pectens, a small entosternite with ten pairs of muscles inserted into it. The supra-pectinal entosternite lies ventral to the nerve cords.

In Mygale (figs. 5 and 6) the form of the entosternite is more like that of Limulus than is that of Scorpio. The anterior notch Ph.N. is similar to that in Limulus, whilst the imbricate triangular pieces of the posterior median region resemble the similarly-placed structures of Limulus in a striking manner.

It must be confessed that we are singularly ignorant as to the functional significance of these remarkable organs—the entosternites. Their movement in an upward or downward direction in Limulus and Mygale must exert a pumping action on the blood contained in the dorsal arteries and the ventral veins respectively. In Scorpio the completion of the horizontal plate by oblique naps, so as to form an actual diaphragm shutting off the cavity of the prosoma from the rest of the body, possibly gives to the organs contained in the anterior chamber a physiological advantage in respect of the supply of arterial blood and its separation from the venous blood of the mesosoma. Possibly the movement of the diaphragm may determine the passage of air into or out of the lung-sacs. Muscular fibres connected with the suctorial pharynx are in Limulus inserted into the entosternite, and the activity of the two organs may be correlated.

5. The Blood and the Blood-vascular System.—The blood fluids of Limulus and Scorpio are very similar. Not only are the blood corpuscles of Limulus more like in form and granulation to those of Scorpio than to those of any Crustacean, but the fluid is in both animals strongly impregnated with the blue-coloured respiratory proteid, haemocyanin. This body occurs also in the blood of Crustacea and of Molluscs, but its abundance in both Limulus and Scorpio is very marked, and gives to the freshly-shed blood a strong indigo-blue tint.

Fig. 20.—View of the ventral surface of the mid-line of the prosomatic region of Limulus polyphemus. The coxae of the five pairs of limbs following the chelicerae were arranged in a series on each side between the mouth, M, and the metasternites, mets.

sf, The sub-frontal median sclerite.

Ch, The chelicerae.

cam, The camerostome or upper lip.

M, The mouth.

pmst, The promesosternal sclerite of chitinous plate, unpaired.

mets, The right and left metasternites (corresponding to the similarly placed pentagonal sternite of Scorpio). Natural size.

(After Lankester.)

Fig. 2l.—Development of the lateral eyes of a scorpion. h, Epidermic cell-layer; mes, mesoblastic connective tissue; n, nerves; II, III, IV, V, depressions of the epidermis in each of which a cuticular lens will be formed.

(From Korschelt and Heider, after Laurie.)

Fig. 22.—Section through the lateral eye of Euscorpius italicus.

lens, Cuticular lens.

nerv c, Retinal cells (nerve-end cells).

rhabd, Rhabdomes.

nerv f, Nerve fibres of the optic nerve.

int, Intermediate cells (lying between the bases of the retinal cells).

(After Lankester and Bourne from Parker and Habwell’s Text book of Zoology, Macmillan & Co.)

Fig. 23.—Section through a portion of the lateral eye of Limulus, showing three ommatidia—A, B and C. hyp, The epidermic cell-layer (so-called hypodermis), the cells of which increase in volume below each lens, l, and become nerve-end cells or retinula-cells, rt; in A, the letters rh point to a rhabdomere secreted by the cell rt; c, the peculiar central spherical cell; n, nerve fibres; mes, mesoblastic skeletal tissue; ch, chitinous cuticle.

(From Korschelt and Heider after Watase.)

The great dorsal contractile vessel or “heart” of Limulus is closely similar to that of Scorpio; its ostia or incurrent orifices are placed in the same somites as those of Scorpio, but there is one additional posterior pair. The origin of the paired arteries from the heart differs in Limulus from the arrangement obtaining in Scorpio, in that a pair of lateral commissural arteries exist in Limulus (as described by Alphonse Milne-Edwards (6)) leading to a suppression of the more primitive direct connexion of the four pairs of posterior lateral arteries and of the great median posterior arteries with the heart itself (fig. 29). The arterial system is very completely developed in both Limulus and Scorpio, branching repeatedly until minute arterioles are formed, not to be distinguished from true capillaries; these open into irregular swollen vessels which are the veins or venous sinuses. A very remarkable feature in Limulus, first described by Owen, is the close accompaniment of the prosomatic nerve centres and nerves by arteries, so close indeed that the great ganglion mass and its out-running nerves are actually sunk in or invested by arteries. The connexion is not so intimate in Scorpio, but is nevertheless a very close one, closer than we find in any other Arthropods in which the arterial system is well developed, e.g. the Myriapoda and some of the arthrostracous Crustacea. It seems that there is a primitive tendency in the Arthropoda for the arteries to accompany the nerve cords, and a “supra-spinal” artery—that is to say, an artery in close relation to the ventral nerve cords—has been described in several cases. On the other hand, in many Arthropods, especially those which possess tracheae, the arteries do not have a long course, but soon open into wide blood sinuses. Scorpio certainly comes nearer to Limulus in the high development of its arterial system, and the intimate relation of the anterior aorta and its branches to the nerve centres and great nerves, than does any other Arthropod.

An arrangement of great functional importance in regard to the venous system must now be described, which was shown in 1883 by Lankester to be common to Limulus and Scorpio. This arrangement has not hitherto been detected in any other class than the Arachnida, and if it should ultimately prove to be peculiar to that group, would have considerable weight as a proof of the close genetic affinity of Limulus and Scorpio.

A, Early condition before the lens is deposited, showing the folding of the epidermic cell-layer into three.

B, Diagram showing the nature of this infolding.

C, Section through the fully formed eye.

h, Epidermic cell-layer.

r, The retinal portion of the same which, owing to the infolding, lies between gl, the corneagen or lens-forming portion, and pr, the post-retinal or capsular portion or fold.

l, Cuticular lens.

g, Line separating lens from the lens-forming or corneagen cells of the epidermis.

n, Nerve fibres.

rh, Rhabdomeres.

(From Korschelt and Heider.)

The great pericardial sinus is strongly developed in both animals. Its walls are fibrous and complete, and it holds a considerable volume of blood when the heart itself is contracted. Opening in pairs in each somite, right and left into the pericardial sinus are large veins, which bring the blood respectively from the gill-books and the lung-books to that chamber, whence it passes by the ostia into the heart. The blood is brought to the respiratory organs in both cases by a great venous collecting sinus having a ventral median position. In both animals the wall of the pericardial sinus is connected by vertical muscular bands to the wall of the ventral venous sinus (its lateral expansions around the lung-books in Scorpio) in each somite through which the pericardium passes. There are seven pairs of these veno-pericardiac vertical muscles in Scorpio, and eight in Limulus (see figs. 30, 31, 32). It is obvious that the contraction of these muscles must cause a depression of the floor of the pericardium and a rising of the roof of the ventral blood sinus, and a consequent increase of volume and flow of blood to each. Whether the pericardium and the ventral sinus are made to expand simultaneously or all the movement is made by one only of the surfaces concerned, must depend on conditions of tension. In any case it is clear that we have in these muscles an apparatus for causing the blood to flow differentially in increased volume into either the pericardium, through the veins leading from the respiratory organs, or from the body generally into the great sinuses which bring the blood to the respiratory organs. These muscles act so as to pump the blood through the respiratory organs.

L, Cuticular or corneous lens.

hy, Epidermic cell-layer.

corn, Its corneagen portion immediately underlying the lens.

ret, Retinula cells.

nf, Nerve fibres.

con. tiss, Connective tissue (mesoblastic skeletal tissue).

(After Lankester and Bourne, Q. J. Mic. Sci., 1883.)

It is not surprising that with so highly developed an arterial system Limulus and Scorpio should have a highly developed mechanism for determining the flow of blood to the respiratory organs. That this is, so to speak, a need of animals with localized respiratory organs is seen by the existence of provisions serving a similar purpose in other animals, e.g. the branchial hearts of the Cephalopoda.

The veno-pericardiac muscles of Scorpio were seen and figured by Newport but not described by him. Those of Limulus were described and figured by Alphonse Milne-Edwards, but he called them merely “transparent ligaments,” and did not discover their muscular structure. They are figured and their importance for the first time recognized in the memoir on the muscular and skeletal systems of Limulus and Scorpio by Lankester, Beck and Bourne (4).

6. Alimentary Canal and Gastric Glands.—The alimentary canal in Scorpio, as in Limulus, is provided with a powerful suctorial pharynx, in the working of which extrinsic muscles take a part. The mouth is relatively smaller in Scorpio than in Limulus—in fact is minute, as it is in all the terrestrial Arachnida which suck the juices of either animals or plants. In both, the alimentary canal takes a straight course from the pharynx (which bends under it downwards and backwards towards the mouth in Limulus) to the anus, and is a simple, narrow, cylindrical tube (fig. 33). The only point in which the gut of Limulus resembles that of Scorpio rather than that of any of the Crustacea, is in possessing more than a single pair of ducts or lateral outgrowths connected with ramified gastric glands or gastric caeca. Limulus has two pairs of these, Scorpio as many as six pairs. The Crustacea never have more than one pair. The minute microscopic structure of the gastric glands in the two animals is practically identical. The functions of these gastric diverticula have never been carefully investigated. It is very probable that in Scorpio they do not serve merely to secrete a digestive fluid (shown in other Arthropoda to resemble the pancreatic fluid), but that they also become distended by the juices of the prey sucked in by the scorpion—as certainly must occur in the case of the simple unbranched gastric caeca of the spiders.

The most important difference which exists between the structure of Limulus and that of Scorpio is found in the hinder region of the alimentary canal. Scorpio is here provided with a single or double pair of renal excretory tubes, which have been identified by earlier authors with the Malpighian tubes of the Hexapod and Myriapod insects. Limulus is devoid of any such tubes. We shall revert to this subject below.

A, Diagram of a retinula of the central eye of a scorpion consisting of five retina-cells (ret), with adherent branched pigment cells (pig).

B, Rhabdom of the same, consisting of five confluent rhabdomeres.

C, Transverse section of the rhabdom of a retinula of the scorpion’s central eye, showing its five constituent rhabdomeres as rays of a star.

D, Transverse section of a retinula of the lateral eye of Limulus, showing ten retinula cells (ret), each bearing a rhabdomere (rhab).

(After Lankester.)

Fig. 27.—Diagram showing the position of the coxal glands of a scorpion, Buthus australis, Lin., in relation to the legs, diaphragm (entosternal flap), and the gastric caeca.

1 to 6, The bases of the six prosomatic limbs.

A, prosomatic gastric gland (sometimes called salivary).

B, Coxal gland.

C, Diaphragm of Newport = fibrous flap of the entosternum.

D, Mesosomatic gastric caeca (so-called liver).

E, Alimentary canal.

(From Lankester, Q. J. Mic. Sci., vol. xxiv. N.S. p. 152.)

7. Ovaries and Spermaries: Gonocoels and Gonoducts.—The scorpion is remarkable for having the specialized portion of coelom from the walls of which egg-cells or sperm-cells are developed according to sex, in the form of a simple but extensive network. It is not a pair of simple tubes, nor of dendriform tubes, but a closed network. The same fact is true of Limulus, as was shown by Owen (7) in regard to the ovary, and by Benham (14) in regard to the testis. This is a very definite and remarkable agreement, since such a reticular gonocoel is not found in Crustacea (except in the male Apus). Moreover, there is a significant agreement in the character of the spermatozoa of Limulus and Scorpio. The Crustacea are—with the exception of the Cirrhipedia—remarkable for having stiff, motionless spermatozoids. In Limulus Lankester found (15) the spermatozoa to possess active flagelliform “tails,” and to resemble very closely those of Scorpio which, as are those of most terrestrial Arthropoda, are actively motile. This is a microscopic point of agreement, but is none the less significant.

In regard to the important structures concerned with the fertilization of the egg, Limulus and Scorpio differ entirely from one another. The eggs of Limulus are fertilized in the sea after they have been laid. Scorpio, being a terrestrial animal, fertilizes by copulation. The male possesses elaborate copulatory structures of a chitinous nature, and the eggs are fertilized in the female without even quitting the place where they are formed on the wall of the reticular gonocoel. The female scorpion is viviparous, and the young are produced in a highly developed condition as fully formed scorpions.

Fig. 28.—The right coxal gland of Limulus polyphemus, Latr.

a2 to a5, Posterior borders of the chitinous bases of the coxae of the second, third, fourth and fifth prosomatic limbs.

b, Longitudinal lobe or stolon of the coxal gland.

c. Its four transverse lobes or outgrowths corresponding to the four coxae.

(From Lankester, loc. cit., after Packard.)

Differences between Limulus and Scorpio.—We have now passed in review the principal structural features in which Limulus agrees with Scorpio and differs from other Arthropoda. There remains for consideration the one important structural difference between the two animals. Limulus agrees with the majority of the Crustacea in being destitute of renal excretory caeca or tubes opening into the hinder part of the gut. Scorpio, on the other hand, in common with all air-breathing Arthropoda except Peripatus, possesses these tubules, which are often called Malpighian tubes. A great deal has been made of this difference by some writers. It has been considered by them as proving that Limulus, in spite of all its special agreements with Scorpio (which, however, have scarcely been appreciated by the writers in question), really belongs to the Crustacean line of descent, whilst Scorpio, by possessing Malpighian tubes, is declared to be unmistakably tied together with the other Arachnida to the tracheate Arthropods, the Hexapods, Diplopods, and Chilopods, which all possess Malpighian tubes.

Fig. 29.—Diagram of the arterial system of A, Scorpio, and B, Limulus. The Roman numerals indicate the body somites and the two figures are adjusted for comparison. ce, Cerebral arteries; sp, supra-spinal or medullary artery; c, caudal artery; l, lateral anastomotic artery of Limulus. The figure B also shows the peculiar neural investiture formed by the cerebral arteries in Limulus and the derivation from this of the arteries to the limbs, III, IV, VI, whereas in Scorpio the latter have a separate origin from the anterior aorta.

From Lankester, “Limulus an Arachnid.”

It must be pointed out that the presence or absence of such renal excretory tubes opening into the intestine appears to be a question of adaptation to the changed physiological conditions of respiration, and not of morphological significance, since a pair of renal excretory tubes of this nature is found in certain Amphipod Crustacea (Talorchestia, &c.) which have abandoned a purely aquatic life. This view has been accepted and supported by Professors Korschelt and Heider (16). An important fact in its favour was discovered by Laurie (17), who investigated the embryology of two species of Scorpio under Lankester’s direction. It appears that the Malpighian tubes of Scorpio are developed from the mesenteron, viz. that portion of the gut which is formed by the hypoblast, whereas in Hexapod insects the similar caecal tubes are developed from the proctodaeum or in-pushed portion of the gut which is formed from epiblast. In fact it is not possible to maintain that the renal excretory tubes of the gut are of one common origin in the Arthropoda. They have appeared independently in connexion with a change in the excretion of nitrogenous waste in Arachnids, Crustacea, and the other classes of Arthropoda when aerial, as opposed to aquatic, respiration has been established—and they have been formed in some cases from the mesenteron, in other cases from the proctodaeum. Their appearance in the air-breathing Arachnids does not separate those forms from the water-breathing Arachnids which are devoid of them, any more than does their appearance in certain Amphipoda separate those Crustaceans from the other members of the class.

Further, it is pointed out by Korschelt and Heider that the hinder portion of the gut frequently acts in Arthropoda as an organ of nitrogenous excretion in the absence of any special excretory tubules, and that the production of such caeca from its surface in separate lines of descent does not involve any elaborate or unlikely process of growth. In other words, the Malpighian tubes of the terrestrial Arachnida are homoplastic with those of Hexapoda and Myriapoda, and not homogenetic with them. We are compelled to take a similar view of the agreement between the tracheal air-tubes of Arachnida and other tracheate Arthropods. They are homoplasts (see 18) one of another, and do not owe their existence in the various classes compared to a common inheritance of an ancestral tracheal system.

Fig. 30.—View from below of a scorpion (Buthus occitanus) opened and dissected so as to show the pericardium with its muscles, the lateral arteries, and the tergo-sternal muscles.

PRO, Prosoma.

dpm, Dorso-plastral muscle.

art, Lateral artery.

tsm1, Tergo-sternal muscle (labelled dv in fig. 31) of the second (pectiniferous) mesosomatic somite; this is the most anterior pair of the series of six, none are present in the genital somite.

tsm4, Tergo-sternal muscle of the fifth mesosomatic somite.

tsm6, Tergo-sternal muscle of the enlarged first metasomatic somite.

Per, Pericardium.

VPM1 to VPM7, The series of seven pairs of veno-pericardiac muscles (labelled pv in fig. 31).

There is some reason to admit the existence of another more anterior pair of these muscles in Scorpio; this would make the number exactly correspond with the number in Limulus.

(After Lankester, Trans. Zool. Soc. vol. xi, 1883.)

Conclusions arising from the Close Affinity of Limulus and Scorpio.—When we consider the relationships of the various classes of Arthropoda, having accepted and established the fact of the close genetic affinity of Limulus and Scorpio, we are led to important conclusions. In such a consideration we have to make use not only of the fact just mentioned, but of three important generalizations which serve as it were as implements for the proper estimation of the relationships of any series of organic forms. First of all there is the generalization that the relationships of the various forms of animals (or of plants) to one another is that of the ultimate twigs of a much-branching genealogical tree. Secondly, identity of structure in two organisms does not necessarily indicate that the identical structure has been inherited from an ancestor common to the two organisms compared (homogeny), but may be due to independent development of a like structure in two different lines of descent (homoplasy). Thirdly, those members of a group which, whilst exhibiting undoubted structural characters indicative of their proper assignment to that group, yet are simpler than and inferior in elaboration of their organization to other members of the group, are not necessarily representatives of the earlier and primitive phases in the development of the group—but are very often examples of retrogressive change or degeneration. The second and third implements of analysis above cited are of the nature of cautions or checks. Agreements are not necessarily due to common inheritance; simplicity is not necessarily primitive and ancestral.

On the other hand, we must not rashly set down agreements as due to “homoplasy” or “convergence of development” if we find two or three or more concurrent agreements. The probability is against agreement being due to homoplasy when the agreement involves a number of really separate (not correlated) coincidences. Whilst the chances are in favour of some one homoplastic coincidence or structural agreement occurring between some member or other of a large group a and some member or other of a large group b, the matter is very different when by such an initial coincidence the two members have been particularized. The chances against these two selected members exhibiting another really independent homoplastic agreement are enormous: let us say 10,000 to 1. The chances against yet another coincidence are a hundred million to one, and against yet one more “coincidence” they are the square of a hundred million to one. Homoplasy can only be assumed when the coincidence is of a simple nature, and is such as may be reasonably supposed to have arisen by the action of like selective conditions upon like material in two separate lines of descent.

So, too, degeneration is not to be lightly assumed as the explanation of a simplicity of structure. There is a very definite criterion of the simplicity due to degeneration, which can in most cases be applied. Degenerative simplicity is never uniformly distributed over all the structures of the organism. It affects many or nearly all the structures of the body, but leaves some, it may be only one, at a high level of elaboration and complexity. Ancestral simplicity is more uniform, and does not co-exist with specialization and elaboration of a single organ. Further: degeneration cannot be inferred safely by the examination of an isolated case; usually we obtain a series of forms indicating the steps of a change in structure—and what we have to decide is whether the movement has been from the simple to the more complex, or from the more complex to the simple. The feathers of a peacock afford a convenient example of primitive and degenerative simplicity. The highest point of elaboration in colour, pattern and form is shown by the great eye-painted tail feathers. From these we can pass by gradual transitions in two directions, viz. either to the simple lateral tail feathers with a few rami only, developed only on one side of the shaft and of uniform metallic coloration—or to the simple contour feathers of small size, with the usual symmetrical series of numerous rami right and left of the shaft and no remarkable colouring. The one-sided specialization and the peculiar metallic colouring of the lateral tail feathers mark them as the extreme terms of a degenerative series, whilst the symmetry, likeness of constituent parts inter se, and absence of specialized pigment, as well as the fact that they differ little from any average feather of birds in general, mark the contour feather as primitively simple, and as the starting-point from which the highly elaborated eye-painted tail feather has gradually evolved.

Applying these principles to the consideration of the Arachnida, we arrive at the conclusion that the smaller and simpler Arachnids are not the more primitive, but that the Acari or mites are, in fact, a degenerate group. This was maintained by Lankester in 1878 (19), again in 1881 (20); it was subsequently announced as a novelty by Claus in 1885 (21). Though the aquatic members of a class of animals are in some instances derived from terrestrial forms, the usual transition is from an aquatic ancestry to more recent land-living forms. There is no doubt, from a consideration of the facts of structure, that the aquatic water-breathing Arachnids, represented in the past by the Eurypterines and to-day by the sole survivor Limulus, have preceded the terrestrial air-breathing forms of that group. Hence we see at once that the better-known Arachnida form a series, leading from Limulus-like aquatic creatures through scorpions, spiders and harvest-men, to the degenerate Acari or mites. The spiders are specialized and reduced in apparent complexity, as compared with the scorpions, but they cannot be regarded as degenerate since the concentration of structure which occurs in them results in greater efficiency and power than are exhibited by the scorpion. The determination of the relative degree of perfection of organization attained by two animals compared is difficult when we introduce, as seems inevitable, the question of efficiency and power, and do not confine the question to the perfection of morphological development. We have no measure of the degree of power manifested by various animals—though it would be possible to arrive at some conclusions as to how that “power” should be estimated. It is not possible here to discuss that matter further. We must be content to point out that it seems that the spiders, the pedipalps, and other large Arachnids have not been derived from the scorpions directly, but have independently developed from aquatic ancestors, and from one of these independent groups—probably through the harvest-men from the spiders—the Acari have finally resulted.

After Beck, Trans. Zool. Soc. Vol. xi., 1883.

d, Chelicera.

ch, Chela.

cam, Camerostome.

m, Mouth.

ent, Entosternum.

p, Pecten.

stig1, First pulmonary aperture.

stig4, Fourth pulmonary aperture.

dam, Muscle from carapace to a praeoral entosclerite.

ad, Muscle from carapace to entosternum.

md, Muscle from tergite of genital somite to entosternum (same as dpm in fig. 30).

dv1 to dv6, Dorso-ventral muscles (same as the series labelled tsm in fig. 30).

pv1 to pv7, The seven veno-pericardiac muscles of the right side (labelled VPM in fig. 30).

After Benham, Trans Zool. Soc. vol. xi, 1883.

Suc, Suctorial pharynx.

al, Alimentary canal.

Ph, Pharynx.

M, Mouth.

Est, Entosternum.

VS, Ventral venous sinus.

chi, Chilaria.

go, Genital operculum.

br1 to br5, Branchial appendages,

met, Unsegmented metasoma.

Entap4, Fourth dorsal entapophysis of left side.

tsm, Tergo-sternal muscles, six pairs as in Scorpio (labelled dv in fig. 31).

VPM1 to VPM8, The eight pairs of veno-pericardiac muscles (labelled pv in fig. 31). VPM1 is probably represented in Scorpio, though not marked in figs. 30 and 31.

From Lankester, “Limulua an Arachnid.”

Fig. 33.—The alimentary canal and gastric glands of a scorpion (A) and of Limulus (B).

ps, Muscular suctorial enlargement of the pharynx.

sal, Prosomatic pair of gastric caeca in Scorpio, called salivary glands by some writers.

c1, and c2, The anterior two pairs of gastric caeca and ducts of the mesosomatic region.

c3, c4 and c5. Caeca and ducts of Scorpio not represented in Limulus.

M, The Malpighian or renal caecal diverticula of Scorpio.

pro, The proctodaeum or portion of gut leading to anus and formed embryologically by an inversion of the epiblast at that orifice.

Leaving that question for consideration in connexion with the systematic statement of the characters of the various groups of Arachnida which follows on p. 299, it is well now to consider the following question, viz., seeing that Limulus and Scorpio are such highly developed and specialized forms, and that they seem to constitute as it were the first and second steps in the series of recognized Arachnida—what do we know, or what are we led to suppose with regard to the more primitive Arachnida from which the Eurypterines and Limulus and Scorpio have sprung? Do we know in the recent or fossil condition any such primitive Arachnids? Such a question is not only legitimate, but prompted by the analogy of at least one other great class of Arthropods. The great Arthropod class, the Crustacea, presents to the zoologist at the present day an immense range of forms, comprising the primitive phyllopods, the minute copepods, the parasitic cirrhipedes and the powerful crabs and lobsters, and the highly elaborated sand-hoppers and slaters. It has been insisted, by those who accepted Lankester’s original doctrine of the direct or genetic affinity of the Chaetopoda and Arthropoda, that Apus and Branchipus really come very near to the ancestral forms which connected those two great branches of Appendiculate (Parapodiate) animals. On the other hand, the land crabs are at an immense distance from these simple forms. The record of the Crustacean family-tree is, in fact, a fairly complete one—the lower primitive members of the group are still represented by living forms in great abundance. In the case of the Arachnida, if we have to start their genealogical history with Limulus and Scorpio, we are much in the same position as we should be in dealing with the Crustacea, were the whole of the Entomostraca and the whole of the Arthrostraca wiped out of existence and record. There is no possibility of doubt that the series of forms corresponding in the Arachnidan line of descent, to the forms distinguished in the Crustacean line of descent as the lower grade—the Entomostraca—have ceased to exist, and not only so, but have left little evidence in the form of fossils as to their former existence and nature. It must, however, be admitted as probable that we should find some evidence, in ancient rocks or in the deep sea, of the early more primitive Arachnids. And it must be remembered that such forms must be expected to exhibit, when found, differences from Limulus and Scorpio as great as those which separate Apus and Cancer. The existing Arachnida, like the higher Crustacea, are “nomomeristic,” that is to say, have a fixed typical number of somites to the body. Further, they are like the higher Crustacea, “somatotagmic,” that is to say, they have this limited set of somites grouped in three (or more) “tagmata” or regions of a fixed number of similarly modified somites—each tagma differing in the modification of its fixed number of somites from that characterizing a neighbouring “tagma.” The most primitive among the lower Crustacea, on the other hand, for example, the Phyllopoda, have not a fixed number of somites, some genera—even allied species—have more, some less, within wide limits; they are “anomomeristic.” They also, as is generally the case with anomomeristic animals, do not exhibit any conformity to a fixed plan of “tagmatism” or division of the somites of the body into regions sharply marked off from one another; the head or prosomatic tagma is followed by a trunk consisting of somites which either graduate in character as we pass along the series or exhibit a large variety in different genera, families and orders, of grouping of the somites. They are anomotagmic, as well as anomomeristic.

When it is admitted—as seems to be reasonable—that the primitive Arachnida would, like the primitive Crustacea, be anomomeristic and anomotagmic, we shall not demand of claimants for the rank of primitive Arachnids agreement with Limulus and Scorpio in respect of the exact number of their somites and the exact grouping of those somites; and when we see how diverse are the modifications of the branches of the appendages both in Arachnida and in other classes of Arthropoda (q.v.), we shall not over-estimate a difference in the form of this or that appendage exhibited by the claimant as compared with the higher Arachnids. With those considerations in mind, the claim of the extinct group of the trilobites to be considered as representatives of the lower and more primitive steps in the Arachnidan genealogy must, it seems, receive a favourable judgment. They differ from the Crustacea in that they have only a single pair of prae-oral appendages, the second pair being definitely developed as mandibles. This fact renders their association with the Crustacea impossible, if classification is to be the expression of genetic affinity inferred from structural coincidence. On the contrary, this particular point is one in which they agree with the higher Arachnida. But little is known of the structure of these extinct animals; we are therefore compelled to deal with such special points of resemblance and difference as their remains still exhibit. They had lateral eyes which resemble no known eyes so closely as the lateral eyes of Limulus. The general form and structure of their prosomatic carapace are in many striking features identical with that of Limulus. The trilobation of the head and body—due to the expansion and flattening of the sides or “pleura” of the tegumentary skeleton—is so closely repeated in the young of Limulus that the latter has been called “the trilobite stage” of Limulus (fig. 42 compared with fig. 41). No Crustacean exhibits this trilobite form. But most important of the evidences presented by the trilobites of affinity with Limulus, and therefore with the Arachnida, is the tendency less marked in some, strongly carried out in others, to form a pygidial or telsonic shield—a fusion of the posterior somites of the body, which is precisely identical in character with the metasomatic carapace of Limulus. When to this is added the fact that a post-anal spine is developed to a large size in some trilobites (fig. 38), like that of Limulus and Scorpio, and that lateral spines on the pleura of the somites are frequent as in Limulus, and that neither metasomatic fusion of somites nor post-anal spine, nor lateral pleural spines are found in any Crustacean, nor all three together in any Arthropod besides the trilobites and Limulus—the claim of the trilobites to be considered as representing one order of a lower grade of Arachnida, comparable to the grade Entomostraca of the Crustacea, seems to be established.

The fact that the single pair of prae-oral appendages of trilobites, known only as yet in one genus, is in that particular case a pair of uni-ramose antennae—does not render the association of trilobites and Arachnids improbable. Although the prae-oral pair of appendages in the higher Arachnida is usually chelate, it is not always so; in spiders it is not so; nor in many Acari. The bi-ramose structure of the post-oral limbs, demonstrated by Beecher in the trilobite Triarthrus, is no more inconsistent with its claim to be a primitive Arachnid than is the foliaceous modification of the limbs in Phyllopods inconsistent with their relationship to the Arthrostracous Crustaceans such as Gammarus and Oniscus.

Thus, then, it seems that we have in the trilobites the representatives of the lower phases of the Arachnidan pedigree. The simple anomomeristic trilobite, with its equi-formal somites and equi-formal appendages, is one term of the series which ends in the even more simple but degenerate Acari. Between the two and at the highest point of the arc, so far as morphological differentiation is concerned, stands the scorpion; near to it in the trilobite’s direction (that is, on the ascending side) are Limulus and the Eurypterines—with a long gap, due to obliteration of the record, separating them from the trilobite. On the other side—tending downwards from the scorpion towards the Acari—are the Pedipalpi, the spiders, the book-scorpions, the harvest-men and the water-mites.

The strange nobody-crabs or Pycnogonids occupy a place on the ascending half of the arc below the Eurypterines and Limulus. They are strangely modified and degenerate, but seem to be (as explained in the systematic review) the remnant of an Arachnidan group holding the same relation to the scorpions which the Laemodipoda hold to the Podophthalmate Crustacea.

We have now to offer a classification of the Arachnida and to pass in review the larger groups, with a brief statement of their structural characteristics.

In the bibliography at the close of this article (referred to by leaded arabic numerals in brackets throughout these pages), the titles of works are given which contain detailed information as to the genera and species of each order or sub-order, their geographical distribution and their habits and economy so far as they have been ascertained. The limits of space do not permit of a fuller treatment of those matters here.

Tabular Classification of the Arachnida.

Class. ARACHNIDA.

Grade A. ANOMOMERISTICA.

Sub-Class. TRILOBITAE.
Orders. Not satisfactorily determined.

Grade B. NOMOMERISTICA.

Sub-Class I. PANTOPODA.
Order 1. Nymphonomorpha.
Order 2. Ascorhynchomorpha.
Order 3. Pycnogonomorpha.
Sub-Class II. EU-ARACHNIDA.
Grade a. delobranchia, Lankester (vel hydropneustea, Pocock).
Order 1. Xiphosura.
Order 2. Gigantostraca.
Grade b. embolobranchia, Lankester (vel aeropneustea, Pocock).
Section α. Pectinifera.
Order 1. Scorpionidea.
Sub-order a. Apoxypoda.
Sub-order b. Dionychopoda.
Section β. Epectinata.
Order 2. Pedipalpi.
Sub-order a. Uropygi.
Tribe 1. Urotricha.
Tribe 2. Tartarides.
Sub-order b. Amblypygi.
Order 3. Araneae.
Sub-order a. Mesothelae.
Sub-order b. Opisthothelae.
Tribe 1. Mygalomorphae.
Tribe 2. Arachnomorphae.
Order 4. Palpigradi (= Microthelyphonidae).
Order 5. Solifugae (= Mycetophorae).
Order 6. Pseudoscorpiones (= Chelonethi).
Sub-order a. Panctenodactyli.
Sub-order b. Hemirtenodactyli.
Order 7. Podogona (= Ricinulel).
Order 8. Opiliones.
Sub-order a. Laniatores.
Sub-order b. Palpatores.
Sub-order c. Anepignathi.
Order 9. Rhynchostomi (= Acari).
Sub-order a. Notostigmata.
Sub-order b. Cryptostigmata.
Sub-order c. Metastigmata.
Sub-order d. Prostigmata.
Sub-order e. Astigmata.
Sub-order f. Vermiformia.
Sub-order g. Tetrapoda.

Class. ARACHNIDA.—Euarthropoda having two prosthomeres (somites which have passed from a post-oral to a prae-oral position), the appendages of the first represented by eyes, of the second by solitary rami which are rarely antenniform, more usually chelate. A tendency is exhibited to the formation of a metasomatic as well as a prosomatic carapace by fusion of the tergal surfaces of the somites. Intermediate somites forming a mesosoma occur, but tend to fuse superficially with the metasomatic carapace or to become co-ordinated with the somites of the metasoma, whether fused or distinct to form one region, the opisthosoma (abdomen of authors). In the most highly developed forms the two anterior divisions (tagmata) of the body, prosoma and mesosoma, each exhibit six pairs of limbs, pediform and plate-like respectively, whilst the metasoma consists of six limbless somites and a post-anal spine. The genital apertures are placed in the first somite following the prosoma, excepting where a praegenital somite, usually suppressed, is retained. Little is known of the form of the appendages in the lowest archaic Arachnida, but the tendency of those of the prosomatic somites has been (as in the Crustacea) to pass from a generalized bi-ramose or multi-ramose form to that of uni-ramose antennae, chelae and walking legs.

The Arachnida are divisible into two grades of structure—according to the fixity or non-fixity of the number of somites building up the body:—

Grade A (of the Arachnida). ANOMOMERISTICA.—Extinct archaic Arachnida, in which (as in the Entomostracous Crustacea) the number of well-developed somites may be more or less than eighteen and may be grouped only as head (prosoma) and trunk or may be further differentiated. A telsonic tergal shield of greater or less size is always present, which may be imperfectly divided into well-marked but immovable tergites indicating incompletely differentiated somites. The single pair of palpiform appendages in front of the mouth has been found in one instance to be antenniform, whilst the numerous post-oral appendages in the same genus were bi-ramose. The position of the genital apertures is not known. Compound lateral eyes present; median eyes wanting. The body and head have the two pleural regions of each somite flattened and expanded on either side of the true gut-holding body-axis. Hence the name of the sub-class signifying tri-lobed, a condition realized also in the Xiphosurous Arachnids. The members of this group, whilst resembling the lower Crustacea (as all lower groups of a branching genealogical tree must do), differ from them essentially in that the head exhibits only one prosthomere (in addition to the eye-bearing prosthomere) with palpiform appendages (as in all Arachnida) instead of two. The Anomomeristic Arachnida form a single sub-class, of which only imperfect fossil remains are known.

Fig. 34.—Restoration of Triarthrus Becki, Green, as determined by Beecher from specimens obtained from the Utica Slates (Ordovician), New York. A, dorsal; B, ventral surface. In the latter the single pair of antennae springing up from each side of the camerostome or hypostome or upper lip-lobe are seen. Four pairs of appendages besides these are seen to belong to the cephalic tergum. All the appendages are pediform and bi-ramose; all have a prominent gnathobase, and in all the exopodite carries a comb-like series of secondary processes.

Sub-class (of the Anomomeristica). TRILOBITAE.—The single sub-class Trilobitae constitutes the grade Anomomeristica. It has been variously divided into orders by a number of writers. The greater or less evolution and specialization of the metasomatic carapace appears to be the most important basis for classification—but this has not been made use of in the latest attempts at drawing up a system of the Trilobites. The form of the middle and lateral regions of the prosomatic shield has been used, and an excessive importance attached to the demarcation of certain areas in that structure. Sutures are stated to mark off some of these pieces, but in the proper sense of that term as applied to the skeletal structures of the Vertebrata, no sutures exist in the chitinous cuticle of Arthropoda. That any partial fusion of originally distinct chitinous plates takes place in the cephalic shield of Trilobites, comparable to the partial fusion of bony pieces by suture in Vertebrata, is a suggestion contrary to fact.

The Trilobites are known only as fossils, mostly Silurian and prae-Silurian; a few are found in Carboniferous and Permian strata. As many as two thousand species are known. Genera with small metasomatic carapace, consisting of three to six fused segments distinctly marked though not separated by soft membrane, are Harpes, Paradoxides and Triarthrus (fig. 34). In Calymene, Homalonotus and Phacops (fig. 38) from six to sixteen segments are clearly marked by ridges and grooves in the metasomatic tagma, whilst in Illaenus the shield so formed is large but no somites are marked out on its surface. In this genus ten free somites (mesosoma) occur between the prosomatic and metasomatic carapaces. Asaphus and Megalaspis (fig. 39) are similarly constituted. In Agnostus (fig. 40) the anterior and posterior carapaces constitute almost the entire body, the two carapaces being connected by a mid-region of only two free somites. It has been held that the forms with a small number of somites marked in the posterior carapace and numerous free somites between the anterior and posterior carapace, must be considered as anterior to those in which a great number of posterior somites are traceable in the metasomatic carapace, and that those in which the traces of distinct somites in the posterior or metasomatic carapace are most completely absent must be regarded as derived from those in which somites are well marked in the posterior carapace and similar in appearance to the free somites. The genus Agnostus, which belongs to the last category, occurs abundantly in Cambrian strata and is one of the earliest forms known. This would lead to the supposition that the great development of metasomatic carapace is a primitive and not a late character, were it not for the fact that Paradoxides and Atops, with an inconspicuous telsonic carapace and numerous free somites, are also Cambrian in age, the latter indeed anterior in horizon to Agnostus.

On the other hand, it may well be doubted whether the pygidial or posterior carapace is primarily due to a fusion of the tergites of somites which were previously movable and well developed. The posterior carapace of the Trilobites and of Limulus is probably enough in origin a telsonic carapace—that is to say, is the tergum of the last segment of the body which carries the anus. From the front of this region new segments are produced in the first instance, and are added during growth to the existing series. This telson may enlarge, it may possibly even become internally and sternally developed as partially separate somites, and the tergum may remain without trace of somite formation, or, as appears to be the case in Limulus, the telson gives rise to a few well-marked somites (mesosoma and two others) and then enlarges without further trace of segmentation, whilst the chitinous integument which develops in increasing thickness on the terga as growth advances welds together the unsegmented telson and the somites in front of it, which were previously marked by separate tergal thickenings. It must always be remembered that we are liable (especially in the case of fossilized integuments) to attach an unwarranted interpretation to the mere discontinuity or continuity of the thickened plates of chitinous cuticle on the back of an Arthropod. These plates may fuse, and yet the somites to which they belong may remain distinct, and each have its pair of appendages well developed. On the other hand, an unusually large tergal plate, whether terminal or in the series, is not always due to fusion of the dorsal plates of once-separate somites, but is often a case of growth and enlargement of a single somite without formation of any trace of a new somite. For the literature of Trilobites see (22*).

Fig. 35.—Triarthrus Becki, Green. a, Restored thoracic limbs in transverse section of the animal; b, section across a posterior somite; c, section across one of the sub-terminal somites.

(After Beecher.)

Fig. 36.—Triarthrus Becki, Green. Dorsal view of second thoracic leg with and without setae. en, Inner ramus; ex, Outer ramus. Fig. 37.—Deiphon Forbesii, Barr. One of the Cheiruridae. Silurian Bohemia.

(After Beecher.) (From Zittel’s Palaeontology.)

Fig. 38.—Dalmanites Kmulurus, Green. One of the Phacopidae, from the Silurian, New York. Fig. 39.—Megalaspis extenuatus. One of the Asaphidae allied to Illaenus, from the Ordovician of East Gothland, Sweden.

(From Zittel.) (From Zittel.)

Grade B (of the Aracknida) NOMOMERISTICA.—Arachnida in which, excluding from consideration the eye-bearing prosthomere, the somites are primarily (that is to say, in the common ancestor of the grade) grouped in three regions of six—(a) the “prosoma” with palpiform appendages, (b) the “mesosoma” with plate-like appendages, and (c) the “metasoma” with suppressed appendages. A somite placed between the prosoma and mesosoma —the prae-genital somite—appears to have belonged originally to the prosomatic series (which with its ocular prosthomere and palpiform limbs [Pantopoda], would thus consist of eight somites), but to have been gradually reduced. In living Arachnids, excepting the Pantopoda, it is either fused (with loss of its appendages) with the prosoma (Limulus, Scorpio), after embryonic appearance, or is retained as a rudimentary, separate, detached somite in front of the mesosoma, or disappears altogether (excalation). The atrophy and total disappearance of ancestrally well-marked somites frequently take place (as in all Arthropoda) at the posterior extremity of the body, whilst excalation of somites may occur at the constricted areas which often separate adjacent “regions,” though there are very few instances in which it has been recognized. Concentration of the organ-systems by fusion of neighbouring regions (prosoma, mesosoma, metasoma), previously distinct, has frequently occurred, together with obliteration of the muscular and chitinous structures indicative of distinct somites. This concentration and obliteration of somites, often accompanied by dislocation of important segmental structures (such as appendages and nerve-ganglia), may lead to highly developed specialization (individuation, H. Spencer), as in the Araneae and Opiliones, and, on the other hand, may terminate in simplification and degeneration, as in the Acari.

Fig. 40.—Four stages in the development of the trilobite Agnostus nudus. A, Youngest stage with no mesosomatic somites; B and C, stages with two mesosomatic somites between the prosomatic and telsonic carapaces; D, adult condition, still with only two free mesosomatic somites.

(From Korschelt and Heider.)

From Korschelt and Heider, after Barrande.

A, Youngest stage.

B, Older stage with distinct pygidial carapace.

C, Stage with two free mesosomatic somites between the prosomatic and telsonic carapaces.

D, Stace with seven free intermediate somites.

E, Stave with twelve free somites; the telsonic carapace has not increased in size.

a, Lateral eye.

g, So-called facial “suture” (not really a suture).

p, Telsonic carapace.

(from Korschelt and Heider, after Leuckart.)

The most important general change which has affected the structure of the nomomeristic Arachnida in the course of their historic development is the transition from an aquatic to a terrestrial life. This has been accompanied by the conversion of the lamelliform gill-plates into lamelliform lung-plates, and later the development from the lung-chambers, and at independent sites, of tracheae or air-tubes (by adaptation of the vasifactive tissue of the blood-vessels) similar to those independently developed in Peripatus, Diplopoda, Hexapoda and Chilopoda. Probably tracheae have developed independently by the same process in several groups of tracheate Arachnids. The nomomeristic Arachnids comprise two sub-classes—one a very small degenerate offshoot from early ancestors; the other, the great bulk of the class.

Sub-Class I. (of the Nomomeristica). PANTOPODA.—Nomomeristic Arachnids, in which the somites corresponding to mesosoma and metasoma have entirely aborted. The seventh, and sometimes the eighth, leg-bearing somite is present and has its leg-like appendages fully developed. Monomeniscous eyes with a double (really triple) cell-layer formed by invagination, as in the Eu-arachnida, are present The Pantopoda stand in the same relation to Limulus and Scorpio that Cyamus holds to the thoracostracous Crustacea. The reduction of the organism to seven leg-bearing somites, of which the first pair, as in so many Eu-arachnida, are chelate, is a form of degeneration connected with a peculiar quasi-parasitic habit resembling that of the crustacean Laemodipoda. The genital pores are situate at the base of the 7th pair of limbs, and may be repeated on the 4th, 5th, and 6th. In all known Pantopoda the size of the body is quite minute as compared with that of the limbs: the alimentary canal sends a long caecum into each leg (cf. the Araneae) and the genital products are developed in gonocoels also placed in the legs.

From Parker and Harwell’s Text-book of Zoology, after Hoek.

Fig. 43.—One of the Nymphonomorphous Pantopoda, Nymphon hispidum, showing the seven pairs of appendages 1 to 7; ab, the rudimentary opisthosoma; s, the mouth-bearing proboscis.

The Pantopoda are divided into three orders, the characters of which are dependent on variation in the presence of the full number of legs.

Order 1. (of the Pantopoda). Nymphonomorpha, Pocock (nov.) (fig. 43).—In primitive forms belonging to the family Nymphonidae the full complement of appendages is retained—the 1st (mandibular), the 2nd (palpiform), and the 3rd (ovigerous) pairs being well developed in both sexes. In certain derivative forms constituting the family Pallenidae, however, the appendages of the 2nd pair are either rudimentary or atrophied altogether.

Two families: 1. Nymphonidae (genus Nymphon), and 2. Pallenidae (genus Pallene).

Order 2. Ascorhynchomorpha, Pocock (nov.).—Appendages of the 2nd and 3rd pairs retained and developed, as in the more primitive types of Nymphonomorpha; but those of the 1st pair are either rudimentary, as in the Ascorhynchidae, or atrophied, as in the Colossendeidae. In the latter a further specialization is shown in the fusion of the body segments.

Two families. 1. Ascorhynchidae (genera Ascorhynchus and Ammothea); 2. Colossendeidae (genera Colossendeis and Discoarachne).

Order 3. Pycnogonomorpha, Pocock (nov.).—Derivative forms in which the reduction in number of the anterior appendages is carried farther than in the other orders, reaching its extreme in the Pycnogonidae, where the 1st and 2nd pairs are absent in both sexes, and the 3rd pair also are absent in the female. In the Hannoniidae, however, which resemble the Pycnogonidae in the absence of the 3rd pair in the female and of the 2nd pair in both sexes, the 1st pair are retained in both sexes.

Two families: 1. Hannoniidae (genus Hannonia); 2. Pycnogonidae (genera Pycnogonum and Phoxichilus).

Remarks.—The Pantopoda are not known in the fossil condition. They are entirely marine, and are not uncommon in the coralline zone of the sea-coast. The species are few, not more than fifty (23). Some large species of peculiar genera are taken at great depths. Their movements are extremely sluggish. They are especially remarkable for the small size of the body and the extension of viscera into the legs. Their structure is eminently that of degenerate forms. Many frequent growths of coralline Algae and hydroid polyps, upon the juices of which they feed, and in some cases a species of gall is produced in hydroids by the penetration of the larval Pantopod into the tissues of the polyp.

Sub-Class II. (of the Nomomeristic Arachnida). EU-ARACHNIDA.—These start from highly developed and specialized aquatic branchiferous forms, exhibiting a prosoma with six pediform pairs of appendages, an intermediate prae-genital somite, a mesosoma of six somites bearing lamelliform pairs of appendages, and a metasoma of six somites devoid of appendages, and the last provided with a post-anal spine. Median eyes are present, which are monomeniscous, with distinct retinal and corneagenous cell-layers, and placed centrally on the prosoma. Lateral eyes also may be present, arranged in lateral groups, and having a single or double cell-layer beneath the lens. The first pair of limbs is often chelate or prehensile, rarely antenniform; whilst the second, third and fourth may also be chelate, or may be simple palps or walking legs.

An internal skeletal plate, the so-called “entosternite” of fibro-cartilaginous tissue, to which many muscles are attached, is placed between the nerve-cords and the alimentary tract in the prosoma of the larger forms (Limulus, Scorpio, Mygale). In the same and other leading forms a pair of much-coiled glandular tubes, the coxal glands (coelomocoels in origin), is found with a duct opening on the coxa of the fifth pair of appendages of the prosoma. The vascular system is highly developed (in the non-degenerate forms); large arterial branches closely accompany or envelop the chief nerves; capillaries are well developed. The blood-corpuscles are large amoebiform cells, and the blood-plasma is coloured blue by haemocyanin.

The alimentary canal is uncoiled and cylindrical, and gives rise laterally to large gastric glands, which are more than a single pair in number (two to six pairs), and may assume the form of simple caeca. The mouth is minute and the pharynx is always suctorial, never gizzard-like. The gonadial tubes (gonocoels or gonadial coelom) are originally reticular and paired, though they may be reduced to a simpler condition. They open on the first somite of the mesosoma. In the numerous degenerate forms simplification occurs by obliteration of the demarcations of somites and the fusion of body-regions, together with a gradual suppression of the lamelliferous respiratory organs and the substitution for them of tracheae, which, in their turn, in the smaller and most reduced members of the group, may also disappear.

The Eu-arachnida are divided into two grades with reference to the condition of the respiratory organs as adapted to aquatic or terrestrial life.

Grade a (of the Eu-arachnida). delobranchia (Hydropheustea).

Mesosomatic segments furnished with large plate-like appendages, the 1st pair acting as the genital operculum, the remaining pairs being provided with branchial lamellae fitted for breathing oxygen dissolved in water. The prae-genital somite partially or wholly obliterated in the adult. The mouth lying far back, so that the basal segments of all the prosomatic appendages, excepting those of the 1st pair, are capable of acting as masticatory organs. Lateral eyes consisting of a densely packed group of eye-units (“compound” eyes).

ORDER 1. XIPHOSURA.—The prae-genital somite fuses in the embryo with the prosoma and disappears (see fig. 19). Not free-swimming, none of the prosomatic appendages modified to act as paddles; segments of the mesosoma and metasoma (= opisthosoma) not more than ten in number, distinct or coalesced.

Family—Limulidae (Limulus).

” *Belinuridae (Belinurus, Aglaspis, Prestwichia).

” *Hemiaspidae (Hemiaspis, Bunodes).

(From Parker and Haswell, Text book of Zoology after Leuckart.)

Remarks.-The Xiphosura are marine in habit, frequenting the shore. They are represented at the present day by the single genus Limulus (figs. 44 and 45; also figs. 7, 9, 11, to 15 and 20), often termed the king-crab, which occurs on the American coast of the Atlantic Ocean, but not on its eastern coasts, and on the Asiatic coast of the Pacific. The Atlantic species (L. polyphemus) is common on the coasts of the United States, and is known as the king-crab or horse-shoe crab. A single specimen was found in the harbour of Copenhagen in the 18th century, having presumably been carried over by a ship to which it clung.

A species of Limulus is found in the Buntersandstein of the Vosges; L. Walchi is abundant in the Oolitic lithographic slates of Bavaria.

1 to 6, The six prosomatic pairs of appendages.

abd, the solid opisthosomatic carapace.

tels, the post-anal spine (not the telson as the lettering would seem to imply, but only its post-anal portion).

operc, the fused first pair of mesosomatic appendages forming the genital operculum.

(From Parker and Haswell, Text book of Zoology, after Leuckart.)

The genera Belinurus, Aglaspis, Prestwichia, Hemiaspis and Bunodes consist of small forms which occur in Palaeozoic rocks. In none of them are the appendages known, but in the form of the two carapaces and the presence of free somites they are distinctly intermediate between Limulus and the Trilobitae. The young form of Limulus itself (fig. 40) is also similar to a Trilobite so far as its segmentation and trilobation are concerned. The lateral eyes of Limulus appear to be identical in structure and position with those of certain Trilobitae.

Fig. 46.—Eurypterus Fischeri, Eichwald. Silurian of Rootzikil. Restoration after Schmidt. The dorsal aspect is presented showing the prosomatic shield with paired compound eyes and the prosomatic appendages II. to VI. The small first pair of appendages is concealed from view by the carapace, 1 to 12 are the somites of the opisthosoma; 13, the post-anal spine.

(From Zittel’s Text-book of Palaeontology, The Macmillan Co, New York, 1896.)

Order 2. Gigantostraca (figs. 46, 47).—Free-swimming forms, with the appendages of the 6th or 5th and 6th pairs flattened or lengthened to act as oars; segments of mesosoma and metasoma (= opisthosoma), twelve in number.

Appendages of anterior pair very large and chelate.

Sub-order Pterygotomorpha, Pterygotidae (Pterygotus).

Appendages of anterior pair minute and chelate.

Sub-order Eurypteromorpha

Stylonuridae (Stylonurus).
Eurypteridae (Eurypterus, Slimonia).

From Zittel’s Palaeontology.

a, Camerostome or epistoma.

m, Chilarium or metasternite of the prosoma (so-called metastoma).

oc, The compound eyes.

1 to 8, Segments of the sixth prosomatic appendage.

I′ to V′, First five opisthosomatic somites.

7′, Sixth opisthosomatic somite.

[Observe the powerful gnathobases of the sixth pair of prosomatic limbs and the median plates behind m. The dotted line on somite I indicates the position of the genital operculum which was probably provided with branchial lamellae.]

Remarks.—The Gigantostraca are frequently spoken of as “the Eurypterines.” Not more than thirty species are known. They became extinct in Palaeozoic times, and are chiefly found in the Upper Silurian, though extending upwards as far as the Carboniferous. They may be regarded as “macrourous” Xiphosura; that is to say, Xiphosura in which the nomomeristic number of eighteen well-developed somites is present and the posterior ones form a long tail-like region of the body. There still appears to be some doubt whether in the sub-order Eurypteromorpha the first pair of prosomatic appendages (fig. 46) is atrophied, or whether, if present, it has the form of a pair of tactile palps or of minute chelae. Though there are indications of lamelliform respiratory appendages on mesosomatic somites following that bearing the genital operculum, we cannot be said to have any proper knowledge as to such appendages, and further evidence with regard to them is much to be desired. (For literature see Zittel, 22*.)

Grade b (of the Eu-arachnida). EMBOLOBRANCHIA (Aeropneustea).

In primitive forms the respiratory lamellae of the appendages of the 3rd, 4th, 5th and eth, or of the 1st and 2nd mesosomatic somites are sunk beneath the surface of the body, and become adapted to breathe atmospheric oxygen, forming the leaves of the so-called lung-books. In specialized forms these pulmonary sacs are wholly or partly replaced by tracheal tubes. The appendages of the mesosoma generally suppressed; in the more primitive forms one or two pairs may be retained as organs subservient to reproduction or silk-spinning. Mouth situated more forwards than in Delobranchia, no share in mastication being taken by the basal segments of the 5th and 6th pairs of prosomatic appendages. Lateral eyes, when present, represented by separate ocelli.

The prae-genital somite, after appearing in the embryo, either is obliterated (Scorpio, Galeodes, Opilioand others) or is retained as a reduced narrow region of the body, the “waist,” between prosoma and mesosoma. It is represented by a full-sized tergal plate in the Pseudo-scorpiones.

Restored after Thorell’s indications by R.I. Pocock.

Fig. 48.—Dorsal view of a restoration of Palaeophonus nuncius, Thorell. The Silurian scorpion from Gothland.

Section α. Pectinifera.—The primitive distinction between the mesosoma and the metasoma retained, the latter consisting of six somites and the former of six somites in the adult, each of which is furnished during growth with a pair of appendages. Including the prae-genital somite (fig. 16), which is suppressed in the adult, there are thirteen somites behind the prosoma. The appendages of the 1st and 2nd mesosomatic somites persisting as the genital operculum and pectones respectively, those of the 3rd, 4th, 5th and 6th somites (? in Palaeophonus) sinking below the surface during growth in connexion with the formation of the four pairs of pulmonary sacs (see fig. 17). Lateral eyes monostichous.

Order 1. Scorpiones.—Prosoma covered by a single dorsal shield, bearing typically median and lateral eyes; its sternal elements reduced to a single plate lodged between or behind the basal segments of the 5th and 6th pairs of appendages. Appendages of 1st pair tri-segmented, chelate; of 2nd pair chelate, with their basal segments subserving mastication; of 3rd, 4th, 5th and 6th pairs similar in form and function, except that in recent and Carboniferous forms the basal segments of the 3rd and 4th are provided with sterno-coxal (maxillary) lobes, those of the 4th pair meeting in the middle line and underlying the mouth. The five posterior somites of the metasoma constricted to form a “tail,” the post-anal sclerite persisting as a weapon of offence and provided with a pair of poison glands (see figs. 8, 10, 12, 13, 14, 15, 21 and 22).

Sub-order Apoxypoda.—The 3rd, 4th, 5th and 6th pairs of appendages short, stout, tapering, the segments about as wide as long, except the apical, which is distally slender, pointed, slightly curved, and without distinct movable claws.

Family—Palaeophonidae, Palaeophonus (figs. 48 and 49).

Sub-order Dionychopoda.—The 3rd, 4th, 5th and 6th pairs of appendages slender, not evenly tapering, the segments longer than wide; the apical segment short, distally truncate, and provided with a pair of movable claws. Basal segments of the 5th and 6th pairs of appendages abutting against the sternum of the prosoma (see fig. 10 and figs. 51, 52 and 53).

Family—Pandinidae (Pandinus, Opisthophthalmus, Urodacus).

” Vejovidae (Vaejovis, Jurus, Euscorpius, Broteas).

” Bothriuridae (Bothriurus, Cercophonius).

” Buthidae (Buthus, Centrums).

” *Cyclophthalmidae (Cydophthalmus) Carboniferous.

” *Eoscorpiidae (Eoscorpius, Centromachus) Carboniferous.

Fig. 49.—Ventral view of a restoration of Palaeophonus Hunteri, Pocock, the Silurian scorpion from Lesmahagow, Scotland. Restored by R.I. Pocock. The meeting of the coxae of all the prosomatic limbs in front of the pentagonal sternum; the space for a genital operculum; the pair of pectens, and the absence of any evidence of pulmonary stigmata are noticeable in this specimen.

(See Pocock, Quart Jour. Micr. Sci., 1901.)

Remarks on the Order Scorpiones.—The Scorpion is one of the great animals of ancient lore and tradition. It and the crab are the only two invertebrates which had impressed the minds of early men sufficiently to be raised to the dignity of astronomical representation. It is all the more remarkable that the scorpion proves to be the oldest animal form of high elaboration which has persisted to the present day. In the Upper Silurian two specimens of a scorpion have been found (figs. 48, 49), one in Gothland and one in Scotland, which would be recognized at once as true scorpions by a child or a savage. The Silurian scorpion Palaeophonus, differs, so far as obvious points are concerned, from a modern scorpion only in the thickness of its legs and in their terminating in strong spike-like joints, instead of being slight and provided with a pair of terminal claws. The legs of the modern scorpion (fig. 10; fig. 51) are those of a terrestrial Arthropod, such as a beetle; whilst those of the Silurian scorpion are the legs of an aquatic Arthropod, such as a crab or lobster. It is probable that the Silurian scorpion was an aquatic animal, and that its respiratory lamellae were still projecting from the surface of the body to serve as branchiae. No trace of “stigmata,” the orifices of the lung-chambers of modern scorpions, can be found in the Scottish specimen of Palaeophonus, which presents the ventral surface of the animal to view. On the other hand, no trace of respiratory appendages excepting the pectens can be detected in the specimen (see fig. 49).

Fig. 50.—Comparison of the sixth prosomatic limb of a recent scorpion (B), of Palaeophonus (C), and of Limulus (A), showing their agreement in the number of segments; in the existence of a movable spine, Sp, at the distal border of the fifth segment; in the correspondence of the two claws at the free end of the limb of Scorpio with two spines similarly placed in Limulus; and, lastly, in the correspondence of the three talon-like spines carried on the distal margin of segment six of recent scorpions with the four larger but similarly situated spines on the leg of Limulus; s, groove dividing the ankylosed segments 4 and 5 of the Limulus leg into two.

(After Pocock, Q. J. Mic. Sci., 1901.)

From Lankester, Journ. Linn. Soc. Zool. vol. xvi., 1881.

Fossil scorpions of the modern type are found in the Coal Measures. At the present day scorpions of various genera are found in all the warm regions of the world. In Europe they occur as far north as Bavaria and the south of France. The largest species measure 9 in. from the front of the head to the end of the sting, and occur in tropical India and Africa. Between 200 and 300 species are known. The scorpions use their large chelae for seizing prey and for fighting with one another. They never use the sting when (as frequently happens) they attack another scorpion, because, as was ascertained by A.G. Bourne (24), the poison exuded by the sting has no injurious effect on another scorpion nor on the scorpion itself. The stories of a scorpion stinging itself to death when placed in a circle of burning coals are due to erroneous observation. When placed in such a position the scorpion faints and becomes inert. It is found (Bourne, 24) that some species of scorpion faint at a temperature of 40° Cent. They recover on being removed to cooler conditions. A scorpion having seized its prey (usually a large insect, or small reptile or mammal) with the large chelae brings its tail over its head, and deliberately punctures the struggling victim twice with its sting (fig. 52). The poison of the sting is similar to snake-poison (Calmette), and rapidly paralyses animals which are not immune to it. It is probably only sickly adults or young children of the human race who can be actually killed by a scorpion’s sting. When the scorpion has paralysed its prey in this way, the two short chelicerae are brought into play (fig. 53). By the crushing action of their pincers, and an alternate backward and forward movement, they bring the soft blood-holding tissues of the victim close to the minute pin-hole aperture which is the scorpion’s mouth. The muscles acting on the bulb-like pharynx now set up a pumping action (see Huxley, 26); and the juices—but no solid matter, excepting such as is reduced to powder—are sucked into the scorpion’s alimentary canal. A scorpion appears to prefer for its food another scorpion, and will suck out the juices of an individual as large as itself. When this has taken place, the gorged scorpion becomes distended and tense in the mesosomatic region. It is certain that the absorbed juices do not occupy the alimentary canal alone, but pass also into its caecal off-sets which are the ducts of the gastric glands (see fig. 33).

From Lankester, Journ. Linn. Soc. From Lankester, Journ. Linn. Soc.

Fig. 52.—Drawing from life of the Italian scorpion Euscorpius italicus, Herbst, holding a blue-bottle fly with its left chela, and carefully piercing it between head and thorax with its sting. Two insertions of the sting are effected and the fly is instantly paralysed by the poison so introduced into its body. Fig. 53.—The same scorpion carrying the now paralysed fly held in its chelicerae, the chelae liberated for attack and defence. Drawn from life.

All Arachnida, including Limulus, feed by suctorial action in essentially the same way as Scorpio.

Scorpions of various species have been observed to make a hissing noise when disturbed, or even when not disturbed. The sound is produced by stridulating organs developed on the basal joints of the limbs, which differ in position and character in different genera (see Pocock, 27). Scorpions copulate with the ventral surfaces in contact. The eggs are fertilized, practically in the ovary, and develop in situ. The young are born fully formed and are carried by the mother on her back. As many as thirty have been counted in a brood. For information as to the embryology of scorpions, the reader is referred to the works named in the bibliography below. Scorpions do not possess spinning organs nor form either snares or nests, so far as is known. But some species inhabiting sandy deserts form extensive burrows. The fifth pair of prosomatic appendages is used by these scorpions when burrowing, to kick back the sand as the burrow is excavated by the great chelae.

References to works dealing with the taxonomy and geographical distribution of scorpions are given at the end of this article (28).

Section β. Epectinata.—The primitive distinction between the mesosoma and the metasoma wholly or almost wholly obliterated, the two regions uniting to form an opisthosoma, which never consists of more than twelve somites and never bears appendages or breathing-organs behind the 4th somite. The breathing-organs of the opisthosoma, when present, represented by two pairs of stigmata, opening either upon the 1st and 2nd (Pedipalpi) or the 2nd and 3rd somites (Solifugae, Pseudo-scorpiones), or by a single pair upon the 3rd (? 2nd) somite (Opiliones) of the opisthosoma, there being rarely an additional stigma on the 4th (some Solifugae). The appendages of the 2nd somite of the opisthosoma absent, rarely minute and bud-like (some Amblypygi), never pectiniform. A prae-genital somite is often present either in a reduced condition forming a waist (Pedipalpi, Araneae, Palpigradi) or as a full-sized tergal plate (Pseudo-scorpiones); in some it is entirely atrophied (Solifugae, Holosomata, and Rhynchostomi). Lateral eyes when present diplostichous.

Remarks.—The Epectinate Arachnids do not stand so close to the aquatic ancestors of the Embolobranchia as do the Pectiniferous scorpions. At the same time we are not justified in supposing that the scorpions stand in any way as an intermediate grade between any of the existing Epectinata and the Delobranchia. It is probable that the Pedipalpi, Araneae, and Podogona have been separately evolved as distinct lines of descent from the ancient aquatic Arachnida. The Holosomata and Rhynchostomi are probably offshoots from the stem of the Araneae, and it is not unlikely (in view of the structure of the prosomatic somites of the Tartarides) that the Solifugae are connected in origin with the Pedipalpi. The appearance of tracheae in place of lung-sacs cannot be regarded as a starting-point for a new line of descent comprising all the tracheate forms; tracheae seem to have developed independently in different lines of descent. On the whole, the Epectinata are highly specialized and degenerate forms, though there are few, if any, animals which surpass the spiders in rapidity of movement, deadliness of attack and constructive instincts.

From Lankester, Q. J. Mic. Sci. N.S. vol. xxi., 1881.

A, Ventral view.

I, Chelicera (detached).

II, Chelae.

III, Palpiform limb.

IV to VI, The walking legs.

stc, Sterno-coxal process (gnathobase) of the chelae.

st1, Anterior sternal plate of the prosoma.

st2, Posterior sternal plate of the prosoma.

pregen, Position of the prae-genital somite (not seen).

l, l, Position of the two pulmonary sacs of the right side.

1 to 11, Somites of the opisthosoma (mesosoma plus metasoma).

msg, Stigmata of the tergo-sternal muscles.

an, Anus.

B, Dorsal view of the opisthosoma of the same.

pregen, The prae-genital somite.

p, The tergal stigmata of the tergo-sternal muscles.

paf, Post-anal segmented filament corresponding to the post-anal spine of Limulus.

Order 2. Pedipalpi (figs. 54 to 59).—Appendages of 1st pair bisegmented, without poison gland; of 2nd pair prehensile, their basal segments underlying the proboscis, and furnished with sterno-coxal (maxillary) process, the apical segment tipped with a single movable or immovable claw; appendages of 3rd pair different from the remainder, tactile in function, with at least the apical segment many-jointed and clawless. The ventral surface of the prosoma bears prosternal, metasternal and usually mesosternal chitine-plates (fig. 55). A narrow prae-genital somite is present between opisthosoma and prosoma (figs. 55, 57). Opisthosoma consisting of eleven somites, almost wholly without visible appendages. Intromittent organ of male beneath the genital operculum (= sternum of the 1st somite of opisthosoma).

Fig. 55.—Thelyphonus sp. Ventral view of the anterior portion of the body to show the three prosomatic sternal plates a, b, c, and the rudimentary sternal element of the prae-genital somite; opisth 1, first somite of the opisthosoma.

From a drawing made by Pickard—Cambridge, under the direction of R.I. Pocock.

Note.—The possibility of another interpretation of the anterior somites of the mesosoma and the prae-genital somite must be borne in mind. Possibly, though not probably, the somites carrying the two lung-sacs correspond to the first two lung-bearing somites of Scorpio, and it is the genital opening which has shifted. The same caution applies in the case of the Araneae. Excalation of one or of two anterior mesosomatic somites, besides the prae-genital somite, would then have to be supposed to have occurred also.

Fig. 56—Thelyphonus assamensis ♂. Ventral surface of the anterior region of the opisthosoma, the first somite being pushed upwards and forwards so as to expose the subjacent structures. opistho 1, First somite of the opisthosoma; opistho 2, second do.; g, genital aperture; l, edges of the lamellae of the lung-books; m, stigmata of tergo-sternal muscles.

(Original drawing by Pocock.)

Sub-order a. Uropygi.—Prosoma longer than wide, its sternal area very narrow, furnished with a large prosternal and metasternal plate, and often with a small mesosternal sclerite. Appendages of 2nd pair with their basal segments united in the middle line and incapable of lateral movement; appendages of 3rd pair with only the apical segment many-jointed. Opisthosoma without trace of appendages; its posterior somites narrowed to form a movable tail for the support of the post-anal sclerite, which has no poison glands.

Tribe 1. Urotricha.—Dorsal area of prosoma covered with a single shield (? two in Geralinura), bearing median and lateral eyes. Post-anal sclerite modified as a long, many-jointed feeler. Appendages of 2nd pair folding in a horizontal plane, completely chelate, the claw immovably united to the sixth segment. Respiratory organs present in the form of pulmonary sacs.

Family—Thelyphonidae (Thelyphonus (fig. 54), Hypoctonus, *Geralinura).

Tribe 2. Tartarides.—Small degenerate forms with the dorsal area of the prosoma furnished with two shields, a larger in front covering the anterior four somites, and a smaller behind covering the 5th and 6th somites; the latter generally subdivided into a right and left portion. There is also a pair of narrow tergal sclerites interposed between the anterior and posterior shields. Eyes evanescent or absent. Appendages of 2nd pair folding in a vertical plane, not chelate, the claw long and movable. Post-anal sclerite short and undivided. No distinct respiratory stigmata behind the sterna of the 1st and 2nd somites of the opisthosoma.

Family-Hubbardiidae (Schizomus, Hubbardia) (figs. 57-59).

Fig. 57.—Schizomus crassicaudatus, one of the Tartarid Pedipalpi. Ventral view of a female with the appendages cut short near the base. Fig. 58.—Schizomus crassicaudatus, a Tartarid Pedipalp. Dorsal view of a male with the appendages cut short.

a, Prosternum of prosoma.

b, Metasternum of prosoma.

prae-gen, The prae-genital somite.

I opisth, First somite of the opisthosoma.

II opisth, Eleventh somite of the opisthosoma.

pa, Post-anal lobe of the female (compare the jointed filament in Thelyphonus, fig. 54).

I to VI. The prosomatic appendages.

a, Anterior plate.

b, Posterior plate of the prosomatic carapace.

prae-gen, Tergum of the prae-genital somite.

11, The eleventh somite of the opisthosoma.

pa, Post-anal lobe of the male—a conical body with narrow basal stalk.

(Original drawing by Pickard-Cambridge, directed by Pocock.) (Original as preceding.)

Sub-order b. Amblypygi.—Prosoma wider than long, covered above by a single shield bearing median and lateral eyes, which have diplostichous ommatea. Sternal area broad, with prosternal, two mesosternal, and metasternal plates, the prosternum projecting forwards beneath the coxae of the 2nd pair of appendages. Appendages of 2nd pair folding in a horizontal plane; their basal segments freely movable; claw free or fused; basal segments of 4th and 5th pairs widely separated by the sternal area; appendages of 3rd pair with all the segments except the proximal three, forming a many-jointed flagellum. Opisthosoma without post-anal sclerite and posterior caudal elongation: with frequently a pair of small lobate appendages on the sternum of the 3rd somite. Respiratory organs, as in Urotricha.

Family—Phrynichidae (Phrynichus, Damon).

” Admetidae (Admetus, Heterophrynus).

” Charontidae (Charon, Sarax).

(Family ?)—*Graeophonus.

Fig. 59.—Schizomus crassicaudatus, one of the Pedipalpi. Lateral view of a male. II to VI, the prosomatic appendages, the first being concealed (see fig. 58); 5, the fifth, and 11, the eleventh tergites of the opisthosoma; pa, the conical post-anal lobe.

(Original as preceding.)

Remarks.—The Pedipalpi are confined to the tropics and warmer temperate regions of both hemispheres. Fossil forms occur in the Carboniferous. The small forms known as Schizomus and Hubbardia are of special interest from a morphological point of view. The Pedipalpi have no poison glands. (Reference to literature (29).)

Fig. 60.—Liphistius desultor, Schiödte, one of the Araneae Mesothelae. Dorsal view. I to VI, the prosomatic appendages; 4, 5, 6, the fourth, fifth and sixth tergites of the opisthosoma. Between the bases of the sixth pair of limbs and behind the prosomatic carapace is seen the tergite of the small prae-genital somite.

(Original by Pickard-Cambridge and Pocock.)

Order 3. Araneae (figs. 60 to 64.).—Prosoma covered with a single shield and typically furnished with median and lateral eyes of diplostichous structure, as in the Amblypygi. The sternal surface wide, continuously chitinized, but with prosternal and metasternal elements generally distinguishable at the anterior and posterior ends respectively of the large mesosternurm. Prosternum underlying the proboscis. Appendages of 1st pair have two segments, as in Pedipalpi, but are furnished with poison gland, and are retroverts. Appendages of 2nd pair not underlying the mouth, but freely movable and, except in primitive forms, furnished with a maxillary lobe; the rest of the limb like the legs, tipped with a single claw and quite unmodified (except in ♂). Remaining pairs of appendages similar in form and function, each tipped with two or three claws. Opisthosoma when segmented showing the same number of somites as in the Pedipalpi; usually unsegmented, the prae-genital somite constricted to form the waist; the appendages of its 3rd and 4th somites retained as spinning mammillae. Respiratory organs (see fig. 63, stg), as in the Amblypygi, or with the posterior pair, rarely the anterior pair as well, replaced by tracheal tubes. Intromittent organ of male in the apical segment of the 2nd prosomatic appendage.

Fig. 61.—Liphistius desultor. Ventral view with the prosomatic appendages cut short excepting the chelicerae (1) whose sharp retroverts are seen. Between the bases of the prosomatic limbs an anterior and a posterior sternal plate (black) are seen. 1, The sternum of the first opisthosomatic or genital somite covering the genital aperture and the first pair of lung-sacs. In front of it the narrow waist is formed by the soft sternal area of the praegenital somite; 2, the sternite of the second opisthosomatic somite covering the posterior pair of lung-sacs; 3 and 4, the spinning appendages (limbs) of the opisthosoma; a, inner, b, outer ramus of the appendage; 11, sternite of the eleventh somite of the opisthosoma: in front of it other rudimentary sternites; an, anus.

(Original as above.)

Sub-order a. Mesothelae (see figs. 60 to 62).—Opisthosoma distinctly segmented, furnished with 11 tergal plates, as in the Amblypygi; the ventral surface of the 1st and 2nd somites with large sternal plates, covering the genital aperture and the two pairs of pulmonary sacs, the sternal plates from the 6th to the 11th somites represented by integumental ridges, weakly chitinized in the middle. The two pairs of spinning appendages retain their primitive position in the middle of the lower surface of the opisthosoma far in advance of the anus on the 3rd and 4th somites, each appendage consisting of a stout, many-jointed outer branch and a slender, unsegmented inner branch. Prosoma as in the Mygalomorphae, except that the mesosternal area is long and narrow.

Family—Liphistiidae (Liphistius, *Arthrolycosa).

Sub-order b. Opisthothelae (see fig. 63).—Opisthosoma without trace of separate terga and sterna, the segmentation merely represented posteriorly by slight integumental folds and the sterna of the 1st and 2nd somites by the opercular plates of the pulmonary sacs. The spinning appendages migrate to the posterior end of the opisthosoma and take up a position close to the anus; the inner branches of the anterior pair either atrophy or are represented homogenetically by a plate, the cribellum, or by an undivided membranous lobe, the colulus.

I to VI, Appendages of the prosoma cut off at the base.

o, Ocular tubercle.

prae-gen, The prae-genital somite.

1 and 2, Sternites of the first and second opisthosomatic somites.

3 and 4, Appendages of the third and fourth opisthosomatic somites, which are the spinning organs, and in this genus occupy their primitive position instead of migrating to the anal region as in other spiders.

5, Tergite of the fifth opisthosomatic somite.

11, Eleventh opisthosomatic somite; an, Anus.

(Original.)

Tribe 1. Mygalomorphae.—The plane of the articulation of the appendages of the 1st pair to the prosoma (the retrovert) vertical, the basal segment projecting straight forwards at its proximal end, the distal segment or fang closing backwards in a direction subparallel to the long axis of the body. Two pairs of pulmonary sacs.

Families—Theraphosidae (Avicularia, Poecilotheria). Barychelidae (Barychelus, Plagiobothrus). Dipluridae (Diplura, Macrothele). Ctenizidae (Cteniza, Nemesia). Atypidae (Atypus, Calommata).

Tribe 2. Arachnomorpnae.—The plane of the articulation of the appendages of the 1st pair to the prosoma horizontal, the basal segment projecting vertically downwards, at least at its proximal end, the distal segment or fang closing inwards nearly or quite at right angles to the long axis of the body. The posterior pulmonary sacs (except in Hypochilus) replaced by tracheal tubes; the anterior and posterior pairs replaced by tracheal tubes in the Caponiidae.

Principal families—Hypochilidae (Hypochilus). Dysderidae (Dysdera, Segestria). Caponiidae (Caponia, Nops). Filistatidae (Filistata). Uloboridae (Uloborus, Dinopis). Argiapidae (Nephila, Gasteracantha). Pholcidae (Pholcus, Artema). Agelenidae (Tegenuria). Lycosidae (Lycosa). Clubionidae (Clubiona, Olios, Sparassus) Gnaphosidae (Gnaphosa, Hemiclaea). Thomisidae (Thomisus). Attidae (Salticus). Urocteidae (Uroctea). Eresidae (Eresus).

Remarks on the Araneae.—The Spiders are the most numerous and diversified group of the Arachnida; about 2000 species are known. No noteworthy fossil spiders are known; the best-preserved are in amber of Oligocene age. Protolycosa and Arthrolycosa occur in the Carboniferous. Morphologically, the spiders are remarkable for the concentration and specialization of their structure, which is accompanied with high physiological efficiency. The larger species of Bird’s Nest Spiders (Avicularia), the opisthosoma of which is as large as a bantam’s egg, undoubtedly attack young birds, and M’Cook gives an account of the capture in its web by an ordinary house spider of a small mouse. The “retrovert” or bent-back first pair of appendages is provided with a poison gland opening on the fang or terminal segment. Spiders form at least two kinds of constructions—snares for the capture of prey and nests for the preservation of the young. The latter are only formed by the female, which is a larger and more powerful animal than the male. Like the scorpions the spiders have a special tendency to cannibalism, and accordingly the male, in approaching the female for the purpose of fertilizing her, is liable to be fallen upon and sucked dry by the object of his attentions. The sperm is removed by the male from the genital aperture into a special receptacle on the terminal segment of the 2nd prosomatic appendage. Thus held out at some distance from the body, it is cautiously advanced by the male spider to the genital aperture of the female.

I to VI, The six pairs of prosomatic appendages.

a, Copulatory apparatus of the second appendage.

b, Process of the fifth joint of the third appendage.

M, Mouth.

pro, Prosternite of the prosoma.

mes, Mesosternite of the prosoma: observe the contact of the coxae of the sixth pair of limbs behind it; compare Liphistius (fig. 61) where this does not occur.

stg, Lung aperture.

gn, Genital aperture.

a, Anus with a pair of backwardly migrated spinning appendages on each side of it; compare the position of these appendages in Liphistius (fig. 61).

(From Lankester, “Limulus an Arachnid.”)

Fig. 64.—Liphistius desultor. Under side of the uplifted genital or first opisthosomatic somite of the female; g, genital aperture; p, pitted plate, probably a gland for the secretion of adhesive material for the eggs; l, the edges of the lamellae of the lung-books of the first pair.

(Original drawing by Pocock.)

For an account of the courtship and dancing of spiders, of their webs and floating lines, the reader is referred to the works of M‛Cook (30) and the Peckhams (31), whilst an excellent account of the nests of trap-door spiders is given by Moggridge (32). References to systematic works will also be found at the end of this article (33).

Order 4. Palpigradi = Microthelyphonidae (see fig. 65).—Prosoma covered above by three plates, a larger representing the dorsal elements of the first four somites, and two smaller representing the dorsal elements of the 5th and 6th.

Its ventral surface provided with one prosternal, two mesosternal and one metasternal plate. Appendages of 1st pair consisting of three segments, completely chelate, without poison gland; of 2nd pair slender, leg-like, tipped with three claws, the basal segment without sterno-coxal process taking no share in mastication, and widely separated from its fellow of the opposite side; 3rd, 4th, 5th and 6th appendages similar in form to the 2nd and to each other.

Proboscis free, not supported from below by either the prosternum or the basal segments of the appendages of the 2nd pair.

A, Ventral view of prosoma and anterior region of opisthosoma with the appendages cut off near the base; a and b, prosternites; c, mesosternite; and d, metasternite of the prosoma; f, ventral surface of the prae-genital somite; g, sternite of the genital somite (first opisthosomatic somite).

B, Dorsal view. I to VI, prosomatic appendages; 1 opisth, genital somite (first opisthosomatic somite).

C, Lateral view, I to VI, prosomatic appendages; a, b, c, the three tergal plates of the prosoma; prae-gen, the prae-genital somite; 1 to 10, the ten somites of the opisthosoma.

D, Chelicera.

(Original drawing by Pocock and Pickard-Cambridge, after Hansen and Sörensen.)

Opisthosoma consisting of only ten somites, which have no tergal and sternal elements, the prae-genital somite contracted to form a “waist,” as in the Pedipalpi; the last three narrowed to form a caudal support for the many-jointed flagelliform telson, as in the Urotricha. Respiratory organs atrophied.

Family—Koeneniidae (Koenenia).

Remarks.—An extremely remarkable minute form originally described by Grassi (34) from Sicily, and since further described by Hansen (35). Recently the genus has been found in Texas, U.S.A. Only one genus of the order is known.

Order 5. Solifugae = Mycetophorae (see figs. 66 to 69).—Dorsal area of prosoma covered with three distinct plates, two smaller representing the terga of the 5th and 6th somites, and a larger representing those of the anterior four somites, although the reduced terga of the 3rd and 4th are traceable behind the larger plate. The latter bears a pair of median eyes and obsolete lateral eyes on each side. Sternal elements of prosoma almost entirely absent, traces of a prosternum and metasternum alone remaining. Rostrum free, not supported by either the prosternum or the basal segments of the appendages. Appendages of 1st pair large, chelate, bisegmented, articulated to the sides of the head-shield; appendages of 2nd pair simple, pediform, with protrusible (? suctorial) organ, and no claws at the tip; their basal segments united in the middle line and furnished with sterno-coxal process. Remaining pairs of appendages with their basal segments immovably fixed to the sternal surface, similar in form, the posterior three pairs furnished with two claws supported on long stalks; the basal segments of the 6th pair bearing five pairs of tactile sensory organs or malleoli. The prae-genital somite is suppressed. Opisthosoma composed of ten somites. Respiratory organs tracheal, opening upon the ventral surface of the 2nd and 3rd, and sometimes also of the 4th somite of the opisthosoma. A supplementary pair of tracheae opening behind the basal segment of the 4th appendage of the prosoma.

(? Intromittent organ of male lodged on the dorsal side of the 1st pair of prosomatic appendages.)

Families—Hexisopodidae (Hexisopus). Solpugidae (Solpuga, Rhagodes). Galeodidae (Galeodes).

Remarks.—These most strange-looking Arachnids occur in warmer temperate, and tropical regions of Asia, Africa and America. Their anatomy has not been studied, as yet, by means of freshly-killed material, and is imperfectly known, though the presence of the coxal glands was determined by Macleod in 1884. The proportionately enormous chelae (chelicerae) of the first pair of appendages are not provided with poison glands; their bite is not venomous.

I to VI, The six leg-bearing somites of the prosoma.

opisth 1, First or genital somite of the opisthosoma.

ge, Site of the genital aperture.

st, Thoracic tracheal aperture.

l2, Anterior tracheal aperture of the opisthosoma in somite 2 of the opisthosoma.

l3, Tracheal aperture in somite 3 of the opisthosoma.

a, Anus.

(From Lankester, “Limulus an Arachnid.”)

I to VI, Prosomatic appendages.

s, Prosomatic stigma or aperture of the tracheal system.

1, First opisthosomatic sternite covering the genital aperture g.

2, Second opisthosomatic sternite covering the second pair of tracheal apertures sp1.

sp2, The third pair of tracheal apertures.

10, The tenth opisthosomatic somite.

an, The anal aperture.

I to VI, Bases of the prosomatic appendages.

o, Eyes.

a, Lateral region of the cephalic plate to which the first pair of appendages are articulated.

b, Cephalic plate with median eye.

c, Dorsal element of somites bearing third and fourth pairs of appendages.

d, Second plate of the prosoma with fifth pair of appendages.

e, Third or hindermost plate of the prosoma beneath which the sixth pair of legs is articulated.

1, 2, 9, 10, First, second, ninth and tenth somites of the opisthosoma.

an, Anus.

(Original by Pickard-Cambridge and Pocock.) (Original.)

Galeodes has been made the means of a comparison between the structure of the Arachnida and Hexapod insects by Haeckel and other writers, and it was at one time suggested that there was a genetic affinity between the two groups—through Galeodes, or extinct forms similar to it. The segmentation of the prosoma and the form of the appendages bear a homoplastic similarity to the head, pro-, meso-, and meta-thorax of a Hexapod with mandibles, maxillary palps and three pairs of walking legs; while the opisthosoma agrees in form and number of somites with the abdomen of a Hexapod, and the tracheal stigmata present certain agreements in the two cases. Reference to literature (36).

I to VI, The six prosomatic limbs cut short.

o, The eyes.

b, c, Demarcated areae of the cephalic or first prosomatic plate corresponding respectively to appendages I, II, III, and to appendage IV (see fig. 68).

d, Second plate of the prosoma-carrying appendage V.

e, Third plate of the prosoma-carrying appendage VI. The prae-genital somite is absent.

1, First somite of the opisthosoma.

2, Second do.

S, Prosomatic tracheal aperture between legs IV and V.

S′ and S″, Opisthosomatic tracheal apertures.

10, Tenth opisthosomatic somite.

an, Anus.

(Original.)

I to VI, Prosomatic appendages.

o, Sterno-coxal process of the basal segment of the second appendage.

1, Sternite of the genital or first opisthosomatic somite; the prae-genital somite, though represented by a tergum, has no separate ternal plate.

2 and 3, Sternites of the second and third somites of the opisthosoma, each showing a tracheal stigma.

10 and 11, Sternites of the tenth and eleventh somites of the opisthosoma.

an, Anus.

I to VI, The prosomatic appendages.

o, Eyes.

prae-gen, Prae-genital somite.

1, Tergite of the genital or first opisthosomatic somite.

10, Tergite of the tenthsomite of the opisthosoma.

11, The evanescent eleventh somite of the opisthosoma.

an, Anus.

(Original by Pocock and Pickard-Cambridge.) (Original.)

Order 6. Pseudoscorpiones = Chelonethi, also called Chernetidia (see figs. 70, 71, 72).—Prosoma covered by a single dorsal shield, at most furnished with one or two diplostichous lateral eyes; sternal elements obliterated or almost obliterated. Appendages of the 1st pair bisegmented completely chelate, furnished with peculiar organs, the serrula and the lamina. Appendages of 2nd pair very large and completely chelate, their basal segments meeting in the middle line, as in the Uropygi, and provided in front with membranous lip-like processes underlying the proboscis. Appendages of the 3rd, 4th, 5th and 6th pairs similar in form and function, tipped with two claws, their basal segments in contact in the median ventral line. The prae-genital somite wide, not constricted, with large tergal plate, but with its sternal plate small or inconspicuous. Opisthosoma composed, at least in many cases, of eleven somites, the 11th somite very small, often hidden within the both. Respiratory organs in the form of tracheal tubes opening by a pair of stigmata in the 2nd and 3rd somites of the opisthosoma. Intromittent organ of male beneath sternum of the 1st somite of the opisthosoma.

Sub-order a. Panctenodactyli.—Dorsal plate of prosoma (carapace) narrowed in front; the appendages of the 1st pair small, much narrower, taken together, than the posterior border of the carapace. Serrula on movable digit of appendages of 1st pair fixed throughout its length, and broader at its proximal than at its distal end; the immovable digit with an external process.

Family—Cheliferidae (Chelifer (figs. 70, 71, 72), Chiridium).

” Garypidae (Garypus).

I to VI, of the six prosomatic appendages.

o, Eyes.

prae-gen, Tergite of the prae-genital somite.

1, Genital or first opisthosomatic somite.

2, 3, 10, The second, third and tenth somites of the opisthosoma.

11, The minute eleventh somite;

an, the anus.

(Original.)

Sub-order b. Hemictenodactyli.—Dorsal plate of prosoma scarcely narrowed in front; the appendages of the 1st pair large, not much narrower, taken together, than the posterior border of the carapace. The serrula or the movable digit free at its distal end, narrowed at the base; no external lamina on the immovable digit.

Family—Obisiidae (Obisium, Pseudobisium).

” Chthoniidae (Chthonius, Tridenchthonius).

Remarks.—The book-scorpions—so called because they were, in old times, found not unfrequently in libraries—are found in rotten wood and under stones. The similarity of the form of their appendages to those of the scorpions suggests that they are a degenerate group derived from the latter, but the large size of the prae-genital somite in them would indicate a connexion with forms preceding the scorpions. Reference to literature (37).

III to VI, The third, fourth, fifth and sixth appendages of the prosoma.

a, Movable (hinged) sclerite (so-called hood) overhanging the first pair of appendages.

b, Fused terga of the prosoma followed by the opisthosoma of four visible somites.

an, Orifice within which the caudal segments are withdrawn.

E, Extremity of the fifth appendage of the male modified to subserve copulation.

(Original drawing by Pocock and Pickard-Cambridge.)

Order 7. Podogona = Ricinulei (see figs. 73 to 76).—Dorsal area of prosoma furnished with two shields, a larger behind representing, probably, the tergal elements of the somites, and a smaller in front, which is freely articulated to the former and folds over the appendages of the 1st pair. Ventral area without distinct sternal plates. Appendages of 1st pair, bisegmented, completely chelate. Appendages of 2nd pair, with their basal segments uniting in the middle line below the mouth, weakly chelate at apex. Appendages of 3rd, 4th, 5th and 6th pairs similar in form; their basal segments in contact in the middle line and immovably welded, except those of the 3rd pair, which have been pushed aside so that the bases of the 2nd and 4th pairs are in contact with each other. A movable membranous joint between the prosoma and the opisthosoma, the generative aperture opening upon the ventral side of the membrane. Prae-genital somite suppressed; the opisthosma consisting of nine segments, whereof the first and second are almost suppressed and concealed within the joint between the prosoma and the opisthosoma; the following four large and manifest, and the remaining three minute and forming a slender generally-retracted tail like that of Thelyphonus. Respiratory organs tracheal, opening by a pair of spiracles in the prosoma above the base of the fifth appendage on each side. Intromittent organ of male placed at the distal end of the appendage of the 5th pair.

Family—Cryptostemmidae (Cryptostemma, Poliochera), Carboniferous.

Fig. 74.—Cryptostemma Karschii, anterior aspect of the prosoma with the “hood” removed. I to IV, first to fourth appendages of the prosoma; a, basal segment of the second pair of appendages meeting its fellow in the middle line (see fig. 75).

(Original drawing by Pocock and Pickard-Cambridge.)

Remarks on the Podogona.—The name given to this small but remarkable group has reference to the position of the male intromittent organ (fig. 73, E). They are small degenerate animals with a relatively firm integument. Not more than four species and twice that number of specimens are known. They have been found in West Africa and South America. A fact of special interest in regard to them is that the genus Poliochera, from the Coal Measures, appears to be a member of the same group. The name Cryptostemma, given to the first-known genus of the order, described by Guérin-Méneville, refers to the supposed concealment of the eyes by the movable cephalic sclerite. Reference to literature (38).

I to VI, The six pairs of appendages of the prosoma, the last three cut short.

1, 2, 3, 4, The four somites of the opisthosoma.

a. Visible hood overhanging the first pair of appendages.

b, Position of the genital orifice.

c, Part of 3rd appendage.

d, Fourth segment of 2nd appendage. Observe that the basal segment of appendage III does not meet its fellow in the middle line.

(Original drawing by Pocock and Pickard-Cambridge.)

Fig. 76.—Cryptostemma Karschii. Extremity of the fifth pair of appendages of the female for comparison with that of the male E in fig. 73.

Order 8. Opilione (see fig. 77).—Dorsal area of prosoma covered by a single shield usually bearing a pair of eyes. Sternal elements much reduced. Appendages of 1st pair large, three segmented and completely chelate; of 2nd pair either simple and pediform, or prehensile and subchelate; of remaining four pairs, similar in form, ambulatory in function; the basal segment of the 2nd, 3rd and sometimes of the 4th pairs of appendages furnished with sterno-coxal (maxillary) lobe. Opisthosoma confluent throughout its breadth with the prosoma, with the dorsal plate of which its anterior tergal plates are more or less fused; at most ten opisthosomatic somites traceable; the generative aperture thrust far forwards between the basal segments of the 6th appendages. Prae-genital somite suppressed. Respiratory organs tracheal, opening by a pair of stigmata situated immediately behind the basal segments of the 6th pair of appendages on what is probably the sternum of the 2nd opisthosomatic somite and also in some cases upon the 5th segment of the legs.

Intromittent organ of male lying within the genital orifice.

Sub-order a. Laniatores.—Orifice of foetid glands opening above the coxa of the 4th appendage, not raised upon a tubercle. Orifice of coxal gland situated just behind that of the foetid gland. Sternal plate of prosoma long and narrow, with a distinct prosternal element underlying the mouth. Coxae of 4th, 5th and 6th appendages immovable. Appendages of 2nd pair, strong, usually prehensile and spiny. Genital orifice covered by an operculum.

Families—Gonoleptidae (Gonoleptes, Goniasoma).

Biantidae (Biantes).

Oncopodidae (Oncopus, Pelitnus).

Trioenonychidae (Trioenonyx, Acumontia).

Sub-order b. Palpatores.—Orifice of foetid glands opening above the coxa of the 3rd appendage, not raised upon a tubercle. Orifice of coxal gland situated between the coxae of the 5th and 6th appendages. Sternal plate of prosoma usually short and wide, rarely longer than broad; with a larger or smaller prosternal element underlying the mouth. Coxae of 3rd, 4th, 5th and 6th appendages movable or immovable. Appendages of 2nd pair weak, pediform not prehensile. Genital orifice covered by an operculum.

Families—Phalangiidae (Phalangium, Gagrella).

Ischyropsalidae (Ischyropsalis, Taracus).

Nemastomidae (Nemastoma).

Trogulidae (Trogulus, Anelasmocephalus).

Sub-order c. Cyphophthalmi (Anepignathi).—Orifice of foetid glands opening on a tubercle situated near the lateral border of the carapace above the base of the 5th appendage. Orifice of coxal gland probably situated at base of coxa of 5th appendage; sternal plate of prosema minute or absent; no prosternal element underlying the mouth. Coxae of 5th and 6th, and usually also of 4th appendages immovable. Appendages of 2nd pair weak, pediform, not prehensile. Genital orifice not covered by an operculum.

Families—Sironidae (Siro, Pettalus).

Stylocellidae (Stylocellus).

Remarks on the Opiliones.—These include the harvest-men, sometimes called also daddy-long-legs, with round undivided bodies and very long, easily-detached legs. The intromittent organs of the male are remarkable for their complexity and elaboration. The confluence of the regions of the body and the dislocation of apertures from their typical position are results of degeneration. The Opiliones seem to lead on from the Spiders to the Mites. Reference to literature (39).

A, Dorsal view; I to VI, the six prosomatic appendages.

B, Ventral view of the prosoma and of the first somite of the opisthosoma, with the appendages I to VI cut off at the base; a, tracheal stigma; mx, maxillary processes of the coxae of the 3rd pair of appendages; g, genital aperture.

C, Ventral surface of the prosoma and opisthosoma; a, tracheal stigma; b, last somite.

D, Lateral view of the 1st and 2nd pair of appendages.

E, Lateral view of the whole body and two 1st appendages, showing the fusion of the dorsal elements of the prosoma into a single plate, and of those of the opisthosoma into an imperfectly segmented plate continuous with that of the prosoma.

Apparently related to the Opiliones are two extinct groups, the Anthracomarti and Phalangiotarbi, which are not known to have survived the Carboniferous period. In the Anthracomarti the opisthosoma was movably articulated to the prosoma, and consisted of from eight to ten segments furnished with movable lateral plates, the anal segment being overlapped dorsally by a laminate expansion of the preceding segment. The carapace of the prosoma was unsegmented and often bore a pair of eyes. The appendages of the 2nd pair were slender and pediform; those of the 3rd, 4th, 5th and 6th pairs were similar in form and ambulatory in function with their basal segments arranged round a sternal area as in the order Araneae. The best-known genera were Anthracomartus and Eophognus.

In the Phalangiotarbi the appendages resembled those of the Anthracomarti, except that the basal segments of the last four pairs were usually approximated in the middle line leaving a long and narrow sternal area between; and the carapace of the prosoma was unsegmented. The prosoma and opisthosoma were broadly confluent and probably immovably welded together. The opisthosoma consisted of eight or nine segments, whereof the anterior five or six were very short in the dorsal region, and the posterior three exceptionally large with the anal orifice terminal.

Several genera have been established, the best-characterized being Geraphognus and Architarbus.

Order 9. Rhynchostomi = Acari (see fig. 78).—Degenerate Arachnids resembling the Opiliones in many structural points, but chiefly distinguishable from them by the following features:—The basal segments of the appendages of the 2nd pair are united in the middle line behind the mouth, those of the 3rd, 4th, 5th and 6th pairs are widely separated and not provided with sterno-coxal (maxillary) lobes, and take no share in mastication; the respiratory stigmata, when present, belong to the prosoma, and the primitive segmentation of the opisthosoma has entirely or almost entirely disappeared.

Sub-order a. Notostigmata.—Opisthosoma consisting of ten segments defined by integumental grooves, each of the anterior four of these furnished with a single pair of dorsally-placed spiracles or tracheal stigmata.

Family—Opilioacaridae (Opilioacarus).

Sub-order b. Cryptostigmata.—Integument hard, strengthened by a continuously chitinized dorsal and ventral sclerite. Tracheae typically opening by stigmata situated in the articular sockets (acetabula) of the 3rd, 4th, 5th and 6th pairs of appendages.

Family—Oribatidae (Oribata, Nothrus, Hoplophora).

Sub-order c. Metastigmata.—Integument mostly like that of the Cryptostigmata. Tracheae opening by a pair of stigmata situated above and behind the base of the 4th or 5th or 6th pair of appendages.

Families—Gamasidae (Gamasus, Pteroptus).

Argasidae (Argas, Ornithodoros).

Ixodidae (Ixodes, Rhipicephalus).

Sub-order d. Prostigmata.—Integument soft, strengthened by special sclerites, those on the ventral surface of the prosoma apparently representing the basal segments of the legs embedded in the skin. Tracheae, except in the aquatic species in which they are atrophied, opening by a pair of stigmata situated close to or above the base of the appendages of the 1st pair (mandibles).

Families—Trombidiidae (Trombidium, Tetranychus).

Hydrachnidae (Hydrachna, Atax).

Halacaridae (Halacarus, Leptognathus).

Bdellidae (Bdella, Eupodes).

A, Lateral view with appendages III to VI removed; 1, plate covering the whole dorsal area, representing the fused tergal sclerites of the prosoma and opisthosoma; 2, similarly-formed ventral plate; 3, tracheal stigma.

B, Dorsal view of the same animal; II to VI, 2nd to 6th pairs of appendages. The 1st pair of appendages both in this and in C are retracted.

C, Ventral view of the same; II to VI as in B; a, genital orifice; b, anus; c, united basal segments of the second pair of appendages; d, basal segment of the 6th prosomatic appendage of the right side. The rest of the appendage, as also of app. Ill, IV and V, has been cut away.

Sub-order e. Astigmata.—Degenerate, mostly parasitic forms approaching the Prostigmata in the development of integumental sclerites and the softness of the skin, but with the respiratory system absent.

Families—Tyroglyphidae (Tyroglyphus, Rhizoglyphus).

Sarcoptidae (Sarcoptes, Analges).

Sub-order f. Vermiformia.—Degenerate atracheate parasitic forms with the body produced posteriorly into an annulated caudal prolongation, and the 3rd, 4th, 5th and 6th pairs of appendages short and only three-jointed.

Family—Demodicidae (Demodex).

Sub-order g. Tetrapoda.—Degenerate atracheate gall-mites in which the body is produced posteriorly and annulated, as in Demodex, but in which the appendages of the 3rd and 4th pairs are long and normally segmented and those of the 5th and 6th pairs entirely absent.

Family—Eriophyidae (Eriophyes, Phyllocoptes).

Remarks on the Rhynchostomi.—The Acari include a number of forms which are of importance and special interest on account of their parasitic habits. The ticks (Ixodes) are not only injurious as blood-suckers, but are now credited with carrying the germs of Texas cattle-fever, just as mosquitoes carry those of malaria. The itch-insect (Sarcoptes scabiei) is a well-known human parasite, so minute that it was not discovered until the end of the 18th century, and “the itch” was treated medicinally as a rash. The female burrows in the epidermis much as the female trap-door spider burrows in turf in order to make a nest in which to rear her young. The male does not burrow, but wanders freely on the surface of the skin. Demodex folliculorum is also a common parasite of the sebaceous glands of the skin of the face in man, and is frequent in the skin of the dog. Many Acari are parasitic on marine and freshwater molluscs, and others are found on the feathers of birds and the hair of mammals. Others have a special faculty of consuming dry, powdery vegetable and animal refuse, and are liable to multiply in manufactured products of this nature, such as mouldy cheese. A species of Acarus is recorded as infesting a store of powdered strychnine and feeding on that drug, so poisonous to larger organisms. Reference to literature (40).

Authorities cited by numbers in the text.—1. Strauss-Dürckheim (as reported by MM. Riester and Sanson in an appendix to the sixth volume of the French translation of Meckel’s Anatomy, 1829); 2. Lankester, “Limulus an Arachnid,” Quart. Journ. Micr. Sci. vol. xxi. N.S., 1881; 3. Idem, “On the Skeletotrophic Tissues of Limulus, Scorpio and Mygale,” Quart. Journ. Micr. Sci. vol. xxiv. N.S., 1884; 4. Idem. Trans. Zool. Soc. vol. xi., 1883; 5. Lankester and A.G. Bourne, “Eyes of Limulus and Scorpio,” Quart. Journ. Micr. Sci. vol. xxiii. N.S., Jan. 1883; 6. Milne-Edwards, A., “Recherches sur l’anatomie des Limules,” Ann. Sci. Nat. 5th Series, Zoologie, vol. xvii., 1873; 7. Owen, Richard, “Anatomy of the King-Crab,” Trans. Linn. Soc. Lond., vol. xxviii., 1872; 8. Kishinouye, “Development of Limulus longispina,” Journal of the Science College of Japan, vol. v., 1892; 9. Brauer, “Development of Scorpion,” Zeitschrift für wiss. Zoologie, vol. lix., 1895; 10. Hansen, H.J., “Organs and Characters in Different Orders of Arachnida,” Entomol. Meddel. vol. iv. pp. 137-149; 11. Watase, “On the Morphology of the Compound Eyes of Arthropods,” Studies from the Biolog. Lab. Johns Hopkins University, vol. iv. pp 287-334; 12. Newport, George, “Nervous and Circulatory Systems in Myriapoda and Macrourous Arachnids,” Phil. Trans. Roy. Soc., 1843; 13. Lankester, “Coxal Glands of Limulus, Scorpio and Mygale,” Quart. Journ. Micr. Sci. vol. xxiv. N.S., 1884; 13A. W. Patten and A.P. Hazen, “Development of the Coxal Glands of Limulus,” Journ. of Morphology, vol. xvi., 1900; 13B. Bernard, “Coxal Glands of Scorpio,” Ann. and Mag. Nat. Hist. vol. xii., 1893, p. 55; 14. Benham, “Testis of Limulus,” Trans. Linn. Soc., 1882; 15. Lankester, “Mobility of the Spermatozoa of Limulus,” Quart. Journ. Micr. Sci. vol. xviii. N.S., 1878; 16. Korschelt and Heider, Entwickelungsgeschichte (Jena, 1892), ibique citata; 17. Laurie, M., “The Embryology of a Scorpion,” Quart. Journ. Micr. Sci. vol. xxxi. N.S., 1890, and “On Development of Scorpio fulvipes,” ibid. vol. xxxii., 1891; 18. Lankester (Homoplasy and Homogeny), “On the Use of the term Homology in Modern Zoology,” Ann. and Mag. Nat. Hist., 1870; 19. Idem, “Degeneration, a Chapter in Darwinism,” 1878, reprinted in the Advancement of Science (Macmillan, 1890); 20. Idem, “Limulus an Arachnid,” Q. J. Micr. Sci. vol. xxi. N.S.; 21. Claus, “Degeneration of the Acari and Classification of Arthropoda,” Anzeiger d. k. k. Akad. Wissen. Wien, 1885; see also Ann. and Mag. Nat. Hist. (5) vol. xvii., 1886, p. 364, and vol. xix. p. 225; 22. Lindstrom, G., “Researches on the Visual Organs of the Trilobites,” K. Svenska Vet. Akad. Handl. xxxiv. No. 8, pp. 1-86, Pls. i.-vi., 1901; 22*. Zittel, American edition of his Palaeontology (the Macmillan Co., New York), where ample references to the literature of Trilobitae and Eurypteridae will be found; also references to literature of fossil Scorpions and Spiders; 23. Hoek, “Report on the Pycnogonida,” Challenger Expedition Reports, 1881; Meinert, “Pycnogonida of the Danish Ingolf Expedition,” vol. iii., 1899; Morgan, “Embryology and Phylogeny of the Pycnogonids,” Biol. Lab. Baltimore, vol. v., 1891; 24. Bourne, A.G., “The Reputed Suicide of the Scorpion,” Proc. Roy. Soc. vol. xlii. pp. 17-22; 25. Lankester, “Notes on some Habits of Scorpions,” Journ. Linn. Soc. Zool. vol. xvi. p. 455, 1882; 26. Huxley, “Pharynx of Scorpion,” Quart. Journ. Micr. Sci. vol. viii. (old series), 1860, p. 250; 27. Pocock, “How and Why Scorpions hiss,” Natural Science, vol. ix., 1896; cf. idem, “Stridulating Organs of Spiders,” Ann. and Mag. Nat. Hist. (6), xvi. pp. 230-233; 28. Kraepelin, Das Thierreich (Scorpiones et Pedipalpi) (Berlin, 1899); Peters, “Eine neue Eintheilung der Skorpione,” Man. Akad. Wiss. Berlin, 1861; Pocock, “Classification of Scorpions,” Ann. and Mag. Nat. Hist. (6) xii., 1893; Thorell and Lindstrom, “On a Silurian Scorpion,” Kongl. Svens. Vet. Akad. Handl. xxi. No. 9, 1885; 29. Cambridge, O.P., “A New Family (Tartarides) and Genus of Thelyphonidea,” Ann. and Mag. Nat. Hist. (4) x., 1872, p. 413; Cook, “Hubbardia, a New Genus of Pedipalpi,” Proc. Entom. Soc. Washington, vol. iv., 1899; Thorell, “Tartarides, &c.” Ann. Mus. Genova, vol. xxvii., 1889; 30. M Cook, American Spiders and their Spinning Work (3 vols.; Philadelphia, 1889-1893); 31. Peckham, “On Sexual Selection in Spiders,” Occasional Papers Nat. Hist. Soc. Wisconsin, vol. i. pp. 1-113, 1889; 32. Moggridge, Harvesting Ants and Trap-Door Spiders (1873); 33. Bertkau, Ph., Arch. f. Naturgesch. vol. xlviii. pp. 316-362; Idem, same journal, 1875, p. 235, and 1878, p. 351; Cambridge, O.P., “Araneidea” in Biologia Centr. Americana, vols. i. and ii. (London, 1899); Keyserling, Spinnen Amerikas (Nuremberg, 1880-1892); Pocock, “Liphistius and the Classification of Spiders,” Ann. and Mag. Nat. Hist. (6) x., 1892; Simon, Hist. nat. des Araignées, vols. i. and ii., 1892, 1897; Wagner, “L’Industrie des Araneína,” Mem. Acad. St-Pétersbourg; Idem, “La Mue des Araignées,” Ann. Sci. Nat. vol. vi.; 34. Grassi, G.B. “Intorno ad un nuovo Aracnide artrogastro (Koenenia mirabilis) &c.” Boll. Soc. Ent. Ital. vol. xviii., 1886; 35. H.J. Hansen and Sörensen, “The Order Palpigradi, Thorell (Koenenia), and its Relationships with other Arachnida,” Ent. Tidskr. vol. xviii. pp. 233-240, 1898; Kraepelin, Das Thierreich (Berlin, 1901); 36. Bernard. “Compar. Morphol. of the Galeodidae,” Trans. Linn. Soc. Zool. vol. vi., 1896, ibique citata; Dufour, “Galeodes,” Mém. prés. Acad. Sci. Paris, vol. xvii., 1862; Kraepelin, Das Thierreich (Berlin, 1901); Pocock, “Taxonomy of Solifugae,” Ann. and Mag. Nat. Hist. vol. xx.; 37. Balzan, “Voyage au Vénézuela (Pseudoscorpiones),” Ann. Soc. Entom. France, 1891, pp. 497-522; 38. Guérin-Méneville, Rev. Zool., 1838, p. II; Karsch, “Ueber Cryptostemma Guer.” Berliner entom. Zeitschrift, xxxviii. pp. 25-32, 1892; Thorell, “On an apparently new Arachnid belonging to the family Cryptostemmidae,” Westv. Bihang Svenska Vet. Akad. Handligar, vol. xvii. No. 9, 1892; 39. Hansen and Sorensen, On Two Orders of Arachnida (Cambridge, 1904); Sörensen, “Opiliones laniatores,” Nat. Tidskr. (3) vol. xiv., 1884; Thorell, “Opilioni,” Ann. Mus. Genova, vol. viii., 1876; 40. Berlese, “Acari, &c., in Italia reperta” (Padova, 1892); Canestrini, Acarofauna Italiana (Padova, 1885); Canestrini and Kramer, “Demodicidae and Sarcoptidae” in Das Thierreich (Berlin, 1899); Michael, “British Oribatidae,” Ray Soc.; Idem, “Oribatidae” in Das Thierreich (Berlin, 1898); Idem, “Progress and Present State of Knowledge of Acari,” Journ. Roy. Micr. Soc., 1894; Nalepa, “Phytoptidae,” Das Thierreich (Berlin, 1898); Trouessart, “Classification des Acariens,” Rev. Sci. Nat. de l’ouest. p. 289, 1892; Wagner, Embryonal Entwick, von Ixodes (St Petersburg, 1803); 41. Bertkau, Ph., “Coxaldrusen der Arachniden,” Sitzb. Niederl. Gesellsch., 1885; 42. Patten, W., “Brain and Sense Organs of Limulus,” Quart. Journ. Mic. Sci. vol. xxxv., 1894; see also his “Origin of Vertebrates from Arachnids,” ibid. vol. xxxi.

Authorities not cited by numbers in the text:—

Lung-books:—Berteaux, “Le Poumon des Arachnides,” La Cellule, vol. v. 1891; Jawarowski, “Die Entwick. d. sogen. Lunge bei der Arachniden,” Zeitsch. wiss. Zool. vol. lviii., 1894; Macleod, “Recherches sur la structure et la signification de l’appareil respiratoire des Arachnides,” Arch. d. Biologie. vol. v., 1884; Schneider, A., “Mélanges arachnologiques,” in Tablettes zoologiques, vol. ii. p. 135, 1892; Simmons, “Development of Lung in Spiders,” Amer. Journ. Science, vol. xlviii., 1894. Coxal Glands:—Bertkau, “Ueber die Coxaldrusen der Arachniden,” Sitzb. d. Niederl. Gesellsch., 1885; Loman, “Altes und neues über das Nephridium (die Coxaldrüse) der Arachniden,” Bÿd. tot de Dierkunde, vol. xiv., 1887; Macleod, “Glande coxale chez les Galéodes,” Bull. Acad. Belg. (3) vol. viii., 1884; Pelseneer, “On the Coxal Glands of Mygale,” Proc. Zool. Soc., 1885; Tower, “The External Opening of the brick-red Glands of Limulus,” Zool. Anzeiger, vol. xviii. p. 471, 1895. Ento-sternite:—Schimkewitsch, “Bau und Entwick. des Endosternites der Arachniden,” Zool. Jahrb., Anal. Abtheil., vol. viii., 1894. Embryology:—Balfour, “Development of the Araneina,” Q. J. Micr. Sci. vol. xx., 1880; Kingsley, “The Embryology of Limulus,” Journ. Morphology, vols. vii. and viii.; Kishinouye, “Development of Araneina,” Journ. Coll. Sci. Univ. of Japan, vol. iv., 1890; Locy, “Development of Agelena,” Bull. Mus. Harvard, vol. xii., 1885; Metchnikoff, “Embryologie d. Scorpion,” Zeit. wiss. Zool. vol. xxi., 1871; Idem, “Embryol. Chelifer,” Zeit. wiss. Zool. vol. xxi., 1871; Schimkewitsch, “Développement des Araignées,” Archives d. Biologie, vol. vi. 1887. Sense organs:—Bertkau, “Sinnesorgane der Spinnen,” Arch. f. mikros. Anat. vol. xxvii. p. 589, 1886; Graber, “Unicorneale Tracheaten Auge,” Arch. f. mikr. Anat. vol. xvii., 1879; Grenacher, Gehörorgane der Arthropoden (Göttingen, 1879); Kishinouye, “Lateral Eyes of Spiders,” Zool. Anz. vol. xiv. p. 381, 1891; Purcell, “Phalangiden Augen,” Zool. Anzeiger, vol. xv. p. 461.

General works on Arachnida:—Blanchard, “Les Arachnides” in L’Organisation du regne animal; Gaubert, “Recherches sur les Arachnides,” Ann. Sci. Nat. (7) vol. xiii., 1892; Koch, C., Die Arachniden (16 vols., Nuremberg, 1831-1848); Koch, Keyserling and Sörensen, Die Arachniden Australiens (Nuremberg, 1871-1890); Pocock, Arachnida of British India (London, 1900); Idem, “On African Arachnida,” in Proc. Zool. Soc. and Ann. and Mag. Nat. Hist., 1897-1900; Simon, Les Arachnides de la France (7 vols., Paris, 1874-1881); Thorell, “Arachnida from the Oriental Region,” Ann. Mus. Genova, 1877-1899.

(E. R. L.)

See the article Arthropoda for the use of the term “prosthomere.”

See fig. 12 in the article Arthropoda.

Though ten is the prevailing number of retinula cells and rhabdomeres in the lateral eye of Limulus, Watase states that they may be as few as nine and as many as eighteen.

A great deal of superfluous hypothesis has lately been put forward in the name of “the principle of convergence of characters” by a certain school of palaeontologists. The horse is supposed by these writers to have originated by separate lines of descent in the Old World and the New, from five-toed ancestors! And the important consequences following from the demonstration of the identity in structure of Limulus and Scorpio are evaded by arbitrary and even phantastic invocations of a mysterious transcendental force which brings about “convergence” irrespective of heredity and selection. Morphology becomes a farce when such assumptions are made.

(E. R. L.)

A pair of round tubercles on the labram (camerostome or hypostoma) of several species of Trilobites has been described and held to be a pair of eyes (22). Sense-organs in a similar position were discovered in Limulus by Patten (42) in 1894.

The writer is indebted to R.I. Pocock, assistant in the Natural History departments of the British Museum, for valuable assistance in the preparation of this article and for the classification and definition of the groups of Eu-arachnida here given. The general scheme and some of the details have been brought by the writer into agreement with the views maintained in this article. Pocock accepts those views in all essential points and has, as a special student of the Arachnida, given to them valuable expansion and confirmation. The writer also desires to express his thanks to Messrs. Macmillan & Co. for permission to use figs. 22, 43, 44 and 45, which are taken from Parker and Haswell’s Text-book of Zoology; and to Messrs. Swan Sonnenschein & Co. for the loan of several figures from the translations published by them of the admirable treatise on Embryology by Professors Korschelt and Heider; also to the publishers of the treatise on Palaeontology by Professor Zittel, Herr Oldenbourg and The Macmillan Co., New York, for several cuts of extinct forms.

Pocock suggests that the area marked vii. in the outline figure of the dorsal view of Limulus (fig. 7) may be the tergum of the suppressed prae-genital somite. Embryological evidence must settle whether this is so or not.

ARAD, or Ó-Arad, a town of Hungary, capital of the county of the same name, 159 m. S.E. of Budapest by rail. Pop. (1900) 53,903. It is situated on the right bank of the river Maros, and consists of the inner town and five suburbs. Arad is a modern-built town, and contains many handsome private and public buildings, including a cathedral. It is the seat of a Greek-Orthodox bishop, and possesses a Greek-Orthodox theological seminary, two training schools for teachers—one Hungarian, and the other Rumanian—and a conservatoire for music. The town played an important part in the Hungarian revolution of 1848-49, and possesses a museum containing relics of this war of independence. One of the public squares contains a martyrs’ monument, erected in memory of the thirteen Hungarian generals shot here on the 6th of October 1849, by order of the Austrian general Haynau. It consists of a colossal figure of Hungary, with four allegorical groups, and medallions of the executed generals. Arad is an important railway junction, and has become the largest industrial and commercial centre of south-eastern Hungary. Its principal industries are: distilling, milling, machinery-making, leather-working and saw-milling. A large trade is carried on in grain, flour, alcohol, cattle and wood. Arad was a fortified place, and was captured by the Turks during the wars of the 17th century, and kept by them till the end of that century. The new fortress, built in 1763, although small, was formidable, and played a great role during the Hungarian struggle for independence in 1849. Bravely defended by the Austrian general Berger until the 1st of July 1849, it was then captured by the Hungarian rebels, who made it their headquarters during the latter part of the insurrection. It was from it that Kossuth issued his famous proclamation (11th August 1849), and it was here that he handed over the supreme military and civil power to Görgei. The fortress was recaptured shortly after the surrender of Görgei to the Russians at Világos. The fortress is now used as an ammunition depot.

The town of Uj-Arad, i.e. New Arad (pop. 6124), situated on the opposite bank of the Maros, is practically a suburb of Arad, with which it is connected by a bridge. The town was founded during the Turkish wars of the 17th century. The works erected by the Turks for the capture of the fortress of Arad formed the nucleus of the new town.

Világos, the town where the famous capitulation of Görgei to the Russians took place on the 13th of August 1849, lies 21 m. by rail north-east of Arad.

ARAEOSTYLE (Gr. ἀραιός, weak or widely spaced, and στῦλος, column), an architectural term for the intercolumniation (q.v.) given to those temples where the columns had only timber architraves to carry.

ARAEOSYSTYLE (Gr. ἀραιός, widely spaced, and σύστυλος, with columns set close together), an architectural term applied to a colonnade, in which the intercolumniation (q.v.) is alternately wide and narrow, as in the case of the western porch of St Paul’s cathedral and the east front of the Louvre by Perrault.

ARAGO, DOMINIQUE FRANÇOIS JEAN (1786-1853), French physicist, was born on the 26th of February 1786, at Estagel, a small village near Perpignan, in the department of the eastern Pyrenees. He was the eldest of four brothers. Jean (1788-1836) emigrated to America and became a general in the Mexican army. Jacques Étienne Victor (1799-1855) took part in L.C. de S. de Freycinet’s exploring voyage in the “Uranie” from 1817 to 1821, and on his return to France devoted himself to journalism and the drama. The fourth brother, Étienne Vincent (1802-1892), is said to have collaborated with H. de Balzac in the Héritière de Birague, and from 1822 to 1847 wrote a great number of light dramatic pieces, mostly in collaboration. A strong republican, he was obliged to leave France in 1849, but returned after the amnesty of 1859. In 1879 he was nominated director of the Luxembourg museum.

Showing decided military tastes François Arago was sent to the municipal college of Perpignan, where he began to study mathematics in preparation for the entrance examination of the polytechnic school. Within two years and a half he had mastered all the subjects prescribed for examination, and a great deal more, and, on going up for examination at Toulouse, he astounded his examiner by his knowledge of Lagrange. Towards the close of 1803 he entered the polytechnic school, with the artillery service as the aim of his ambition, and in 1804, through the advice and recommendation of S.D. Poisson, he received the appointment of secretary to the Observatory of Paris. He now became acquainted with Laplace, and through his influence was commissioned, with J.B. Biot, to complete the meridional measurements which had been begun by J.B.J. Delambre, and interrupted since the death of P.F.A. Méchain (1744-1804). The two left Paris in 1806 and began operations among the mountains of Spain, but Biot returned to Paris after they had determined the latitude of Formentera, the southernmost point to which they were to carry the survey, leaving Arago to make the geodetical connexion of Majorca with Ivica and with Formentera.

The adventures and difficulties of the latter were now only beginning. The political ferment caused by the entrance of the French into Spain extended to these islands, and the ignorant populace began to suspect that Arago’s movements and his blazing fires on the top of Mount Galatzo were telegraphic signals to the invading army. Ultimately they became so infuriated that he was obliged to cause himself to be incarcerated in the fortress of Belver in June 1808. On the 28th of July he managed to escape from the island in a fishing-boat, and after an adventurous voyage he reached Algiers on the 3rd of August. Thence he procured a passage in a vessel bound for Marseilles, but on the 16th of August, just as the vessel was nearing Marseilles, it fell into the hands of a Spanish corsair. With the rest of the crew, Arago was taken to Rosas, and imprisoned first in a windmill, and afterwards in the fortress of that seaport, until the town fell into the hands of the French, when the prisoners were transferred to Palamos. After fully three months’ imprisonment they were released on the demand of the dey of Algiers, and again set sail for Marseilles on the 28th of November, but when within sight of their port they were driven back by a northerly wind to Bougie on the coast of Africa. Transport to Algiers by sea from this place would have occasioned a weary stay of three months; Arago, therefore, set out for it by land under conduct of a Mahommedan priest, and reached it on Christmas day. After six months’ stay in Algiers he once again, on the 21st of June 1809, set sail for Marseilles, where he had to undergo a monotonous and inhospitable quarantine in the lazaretto, before his difficulties were over. The first letter he received, while in the lazaretto, was from A. von Humboldt; and this was the origin of a connexion which, in Arago’s words, “lasted over forty years without a single cloud ever having troubled it.”

Through all these vicissitudes Arago had succeeded in preserving the records of his survey; and his first act on his return home was to deposit them in the Bureau des Longitudes at Paris. As a reward for his adventurous conduct in the cause of science, he was in September 1809 elected a member of the Academy of Sciences, in room of J.B.L. Lalande, at the remarkably early age of twenty-three, and before the close of the same year he was chosen by the council of the polytechnic school to succeed G. Monge in the chair of analytical geometry. About the same time he was named by the emperor one of the astronomers of the Royal Observatory, which was accordingly his residence till his death, and it was in this capacity that he delivered his remarkably successful series of popular lectures on astronomy, which were continued from 1812 to 1845.

In 1816, along with Gay-Lussac, he started the Annales de chimie et de physique, and in 1818 or 1819 he proceeded along with Biot to execute geodetic operations on the coasts of France, England and Scotland. They measured the length of the seconds-pendulum at Leith, and in Unst, one of the Shetland isles, the results of the observations being published in 1821, along with those made in Spain. Arago was elected a member of the Board of Longitude immediately afterwards, and contributed to each of its Annuals, for about twenty-two years, important scientific notices on astronomy and meteorology and occasionally on civil engineering, as well as interesting memoirs of members of the Academy.

In 1830, Arago, who always professed liberal opinions of the extreme republican type, was elected a member of the chamber of deputies for the Lower Seine, and he employed his splendid gifts of eloquence and scientific knowledge in all questions connected with public education, the rewards of inventors, and the encouragement of the mechanical and practical sciences. Many of the most creditable national enterprises, dating from this period, are due to his advocacy—such as the reward to L.J.M. Daguerre for the invention of photography, the grant for the publication of the works of P. Fermat and Laplace, the acquisition of the museum of Cluny, the development of railways and electric telegraphs, the improvement of the navigation of the Seine, and the boring of the artesian wells at Grenelle.

In the year 1830 also he was appointed director of the Observatory, and as a member of the chamber of deputies he was able to obtain grants of money for rebuilding it in part, and for the addition of magnificent instruments. In the same year, too, he was chosen perpetual secretary of the Academy of Sciences, in room of J.B.J. Fourier. Arago threw his whole soul into its service, and by his faculty of making friends he gained at once for it and for himself a world-wide reputation. As perpetual secretary it fell to him to pronounce historical éloges on deceased members; and for this duty his rapidity and facility of thought, his happy piquancy of style, and his extensive knowledge peculiarly adapted him.

In 1834 he again visited England, to attend the meeting of the British Association at Edinburgh. From this time till 1848 he led a life of comparative quiet—not the quiet of inactivity, however, for his incessant labours within the Academy and the Observatory produced a multitude of contributions to all departments of physical science,—but on the fall of Louis Philippe he left his laboratory to join in forming the provisional government. He was entrusted with the discharge of two important functions, that had never before been united in one person, viz. the ministry of war and of marine; and in the latter capacity he effected some salutary reforms, such as the improvement of rations in the navy and the abolition of flogging. He also abolished political oaths of all kinds, and, against an array of moneyed interests, succeeded in procuring the abolition of negro slavery in the French colonies.

In the beginning of May 1852, when the government of Louis Napoleon required an oath of allegiance from all its functionaries, Arago peremptorily refused, and sent in his resignation of his post as astronomer at the Bureau des Longitudes. This, however, the prince president, to his credit, declined to accept, and made “an exception in favour of a savant whose works had thrown lustre on France, and whose existence his government would regret to embitter.” But the tenure of office thus granted did not prove of long duration. Arago was now on his death-bed, under a complication of diseases, induced, no doubt, by the hardships and labours of his earlier years. In the summer of 1853 he was advised by his physicians to try the effect of his native air, and he accordingly set out for the eastern Pyrenees. But the change was unavailing, and after a lingering illness, in which he suffered first from diabetes, then from Bright’s disease, complicated by dropsy, he died in Paris on the 2nd of October 1853.

Arago’s fame as an experimenter and discoverer rests mainly on his contributions to magnetism and still more to optics. He found that a magnetic needle, made to oscillate over nonferruginous surfaces, such as water, glass, copper, &c., falls more rapidly in the extent of its oscillations according as it is more or less approached to the surface. This discovery, which gained him the Copley medal of the Royal Society in 1825, was followed by another, that a rotating plate of copper tends to communicate its motion to a magnetic needle suspended over it (“magnetism of rotation”). Arago is also fairly entitled to be regarded as having proved the long-suspected connexion between the aurora borealis and the variations of the magnetic elements.

In optics we owe to him not only important optical discoveries of his own, but the credit of stimulating the genius of A.J. Fresnel, with whose history, as well as with that of E.L. Malus and of Thomas Young, this part of his life is closely interwoven. Shortly after the beginning of the 19th century the labours of these three philosophers were shaping the modern doctrine of the undulatory theory of light. Fresnel’s arguments in favour of that theory found little favour with Laplace, Poisson and Biot, the champions of the emission theory; but they were ardently espoused by Humboldt and by Arago, who had been appointed by the Academy to report on the paper. This was the foundation of an intimate friendship between Arago and Fresnel, and of a determination to carry on together further researches in this subject, which led to the enunciation of the fundamental laws of the polarization of light known by their names (see Polarization). As a result of this work Arago constructed a polariscope, which he used for some interesting observations on the polarization of the light of the sky. To him is also due the discovery of the power of rotatory polarization exhibited by quartz, and last of all, among his many contributions to the support of the undulatory hypothesis, comes the experimentum crucis which he proposed to carry out for comparing directly the velocity of light in air and in water or glass. On the emission theory the velocity should be accelerated by an increase of density in the medium; on the wave theory, it should be retarded. In 1838 he communicated to the Academy the details of his apparatus, which utilized the revolving mirrors employed by Sir C. Wheatstone in 1835 for measuring the velocity of the electric discharge; but owing to the great care required in the carrying out of the project, and to the interruption to his labours caused by the revolution of 1848, it was the spring of 1850 before he was ready to put his idea to the test; and then his eyesight suddenly gave way. Before his death, however, the retardation of light in denser media was demonstrated by the experiments of H.L. Fizeau and J.B.L. Foucault, which, with improvements in detail, were based on the plan proposed by him.

Arago’s Œuvres were published after his death under the direction of J.A. Barral, in 17 vols., 8vo, 1854-1862; also separately his Astronomie populaire, in 4 vols.; Notices biographiques, in 3 vols.; Notices scientifiques, in 5 vols.; Voyages scientifiques, in 1 vol.; Mémoires scientifiques, in 2 vols.; Mélanges, in 1 vol.; and Tables analytiques et documents importants (with portrait), in 1 vol. English translations of the following portions of his works have appeared:—Treatise on Comets, by C. Gold, C.B. (London, 1833); also translated by Smyth and Grant (London, 1861); Hist. éloge of James Watt, by James Muirhead (London, 1839); also translated, with notes, by Lord Brougham; Popular Lectures on Astronomy, by Walter Kelly and Rev. L. Tomlinson (London, 1854); also translated by Dr W.H. Smyth and Prof. R. Grant, 2 vols. (London, 1855); Arago’s Autobiography, translated by the Rev. Baden Powell (London, 1855, 1858); Arago’s Meteorological Essays, with introduction by Humboldt, translated under the superintendence of Colonel Sabine (London, 1855), and Arago’s Biographies of Scientific Men, translated by Smyth, Powell and Grant, 8vo (London, 1857).

ARAGON, or Arragon (in Span. Aragón), a captaincy-general, and formerly a kingdom of Spain; bounded on the N. by the Pyrenees, which separate it from France, on the E. by Catalonia and Valencia, S. by Valencia, and W. by the two Castiles and Navarre. Pop. (1900) 912,711; area, 18,294 sq. m. Aragon was divided in 1833 into the provinces of Huesca, Teruel and Saragossa; an account of its modern condition is therefore given under these names, which have not, however, superseded the older designation in popular usage.

Aragon consists of a central plain, edged by mountain ranges. On the south, east and west, these ranges, though wild and rugged, are of no great elevation, but on the north the Pyrenees attain their greatest altitude in the peaks of Aneto (11,168 ft.) and Monte Perdido (10,998 ft.)—also known as Las Tres Sorores, and, in French, as Mont Perdu. The central pass over the Pyrenees is the Port de Canfranc, on the line between Saragossa and Pau. Aragon is divided by the river Ebro (q.v.), which flows through it in a south-easterly direction, into two nearly equal parts, known as Trans-ibero and Cis-ibero. The Ebro is the principal river, and receives from the north, in its passage through the province, the Arba, the Gallego and the united waters of the Cinca, Esera, Noguera Ribagorzana, Noguera Pallaresa and Segre—the last three belonging to Catalonia. From the south it receives the Jalon and Jiloca (or Xalon and Xiloca) and the Guadalope. The Imperial Canal of Aragon, which was begun by the emperor Charles V. in 1529, but remained unfinished for nearly two hundred years, extends from Tudela to El Burgo de Ebro, a distance of 80 m.; it has a depth of 9 ft., and an average breadth of 69, and is navigable for vessels of about 80 tons. The Royal Canal of Tauste, which lies along the north side of the Ebro, was cut for purposes of irrigation, and gives fertility to the district. Two leagues north-north-east of Albarracin is the remarkable fountain called Cella, 3700 ft. above the sea, which forms the source of the Jiloca; and between this river and the Sierra Molina is an extensive lake called Gallocanta, covering about 6000 acres. The climate is characterized by extreme heat in the summer and cold in the winter; among the mountains the snowfall is heavy, and thunderstorms are frequent, but there is comparatively little rain.

Within a recent geological period, central Aragon was undoubtedly submerged by the sea, and the parched chalky soil remains saturated with salt, while many of the smaller streams run brackish. As the mountains of Valencia and Catalonia effectually bar out the fertilizing moisture of the sea-winds, much of the province is a sheer wilderness, stony, ash-coloured, scarred with dry watercourses, and destitute of any vegetation except thin grass and heaths. In contrast with the splendid fertility of Valencia or the south of France, the landscape of this region, like the rest of central Spain, seems almost a continuation of the north African desert area. There are, however, extensive oak, pine and beech forests in the highlands, and many beautiful oases in the deeply sunk valleys, and along the rivers, especially beside the Ebro, which is, therefore, often called the “Nile of Aragon.” In such oases the flora is exceedingly rich. Wheat, maize, rice, oil, flax and hemp, of fine quality, are grown in considerable quantities; as well as saffron, madder, liquorice, sumach, and a variety of fruits. Merino wool is one of the chief products.

In purity of race the Aragonese are probably equal to the Castilians, to whom, rather than to the Catalans or Valencians, they are also allied in character. The dress of the women is less distinctive than that of the men, who wear a picturesque black and white costume, with knee-breeches, a brilliantly coloured sash, black hempen sandals, and a handkerchief wound round the head.

Three counties—Sobrarbe, situated near the headwaters of the Cinca, Aragon, to the west, and Ribagorza or Ribagorça, to the east—are indicated by tradition and the earliest chronicles as the cradle of the Aragonese monarchy. These districts were never wholly subdued when the Moors overran the country (711-713). Sobrarbe especially was for a time the headquarters of the Christian defence in eastern Spain. About 1035, Sancho III. the Great, ruler of the newly established kingdom of Navarre, which included the three counties above mentioned, bequeathed them to Gonzalez and Ramiro, his sons. Ramiro soon rid himself of his rival, and welded Sobrarbe, Ribagorza and Aragon into a single kingdom, which thenceforward grew rapidly in size and power and shared with Castile the chief part in the struggle against the Moors. The history of this period, which was terminated by the union of Castile and Aragon under Ferdinand and Isabella in 1479, is given, along with a full account of the very interesting constitution of Aragon, under Spain (q.v.). At the height of its power under James I. (1213-1276), the kingdom included Valencia, Catalonia, the Balearic Islands and the considerable territory of Montpellier in France; while Peter III. (1276-1285) added Sicily to his dominions.

The literature relating to Aragon is very extensive. See, in addition to the works cited in the article Spain (section History), “Les Archives d’Aragon et de Navarre,” by L. Cadier, in Bibliothèque de l’École des Chartes, 49 (Paris, 1888). Among the more important original authorities, the following may be selected:—for general history, Anales de la corona de Aragón, by G. Çurita, 3rd ed. in 7 folio volumes (Saragossa, 1668-1671; 1st ed. 1562-1580);—for ecclesiastical history, Teatro histórico de las iglesias de Aragón (Pamplona, 1770-1807); for economic history, História de la economia politica de Aragón, by I.J. de Asso y del Rio (Saragossa, 1798). For the constitution and laws of Aragon, see Orígines del Justicia de Aragón, &c., by J. Ribera Tarrago (Saragossa, 1897), and Instituciones y reyes de Aragón, by V. Balaguér (Madrid, 1896). The topography, inhabitants, art, products, &c., of the kingdom are described in a volume of the series España entitled Aragón, by J.M. Quadrado (Barcelona, 1886).

ARAGONITE, one of the mineral forms of calcium carbonate (CaCO3), the other form being the more common mineral calcite. It crystallizes in the orthorhombic system, and the crystals are either prismatic or acicular in habit. Simple crystals are, however, rare; twinning on the prism planes (M in the figures) being a characteristic feature of the mineral (fig. 1). This twinning is usually often repeated on the same plane (fig. 2), and gives rise to striations on the terminal faces (k) of the crystals; often, also, three crystals are twinned together on two of the prism planes of one of them, producing an apparently hexagonal prism. The mineral is colourless, white or yellowish, transparent or translucent, has a vitreous lustre, and, in fact, is not unlike calcite in general appearance. It may, however, always be readily distinguished from calcite by the absence of any marked cleavage, and by its greater hardness (H. = 3½ − 4) and specific gravity (2.93); further, it is optically biaxial, whilst calcite is uniaxial. It is brittle and has a subconchoidal fracture; on a fractured surface the lustre is decidedly resinous in character.

The mineral was first found, as reddish twinned crystals with the form of six-sided prisms, at Molina in Aragon, Spain, where it occurs with gypsum and small crystals of ferruginous quartz in a red clay. It is from this locality that the mineral takes its name, which was originally spelt arragonite. Fine groups of crystals of the same habit are found in the sulphur deposits of Girgenti in Sicily; also at Herrengrund near Neusohl in Hungary. At many other localities the mineral takes the form of radiating groups of acicular crystals, such as those from the haematite mines of west Cumberland: beautiful feathery forms have been found in a limestone cave in the Transvaal. Fibrous forms are also common. A peculiar coralloidal variety known as flosferri (“flower of iron”) consists of radially arranged fibres: magnificent snow-white specimens of this variety have long been known from the iron mines of Eisenetz in Styria. The calcareous secretions of many groups of invertebrate animals consist of aragonite (calcite is also common); pearls may be specially cited as an example.

Aragonite is a member of the isomorphous group of minerals comprising witherite (BaCO3), strontianite (SrCO3), cerussite (PbCO3) and bromlite ((Ba, Ca)CO3); and crystals of aragonite sometimes contain small amounts of strontium or lead. A variety known as tarnowitzite, from Tarnowitz in Silesia, contains about 5% of lead carbonate.

Aragonite is the more unstable of the two modifications of calcium carbonate. A crystal of aragonite when heated becomes converted into a granular aggregate of calcite individuals: altered crystals of this kind (paramorphs) are not infrequently met with in nature, whilst in fossil shells the original nacreous layer of aragonite has invariably been altered to calcite. From a solution of calcium carbonate in water containing carbon dioxide crystals of calcite are deposited at the ordinary temperature, but from a warm solution aragonite crystallizes out. The thermal springs of Carlsbad deposit spherical concretions of aragonite, forming masses known as pisolite or Sprudelstein.

(L. J. S.)

ARAGUA, one of the smaller states of Venezuela under the redivision of 1904, lying principally within the parallel ranges of the Venezuelan Cordillera, and comprising some of the most fertile and healthful valleys of the republic. It is bounded E. by the Federal District and Maturin, S. by Guárico and W. by Zamora and Carabobo. Pop. (1905, est.) 152,364. Aragua has a short coast-line on the Caribbean west of the Federal District, but has no port of consequence. Cattle, swine and goats are raised, and the state produces coffee, sugar, cacao, beans, cereals and cheese. The climate of the higher valleys is subtropical, the mean annual temperature ranging from 74° to 80° F. The capital, La Victoria (pop. 7800), is situated in the fertile Aragua valley, 1558 ft. above sea-level and 36 m. south-west of Carácas. Other important towns are Barbacoas (pop. 13,109) on the left bank of the Guarico in a highly fertile region, Ciudad de Cura and Maracay (pop. 7500), 56 m. west-south-west of Carácas near the north-east shore of Lake Valencia. The last two towns are on the railway between Carácas and Valencia.

ARAGUAYA, Araguay or Araguia, a river of Brazil and principal affluent of the Tocantins, rising in the Serra do Cayapó, where it is known as the Rio Grande, and flowing in a north by east direction to a junction with the Tocantins at Sao Joao do Araguaya, or Sao Joao das Duas Barras. Its upper course forms the boundary line between Goyaz and Matto Grosso. The river divides into two branches at about 13° 20′ S. lat., and unites again at 10° 30′, forming the large island of Santa Anna or Bananal. The eastern branch, called the Furo, is the one used by boats, as the main channel is obstructed by rapids. Its principal affluent is the Rio das Mortes, which rises in the Serra de Sao Jeronymo, near Cuyabá, Matto Grosso, and is utilized by boatmen going to Pará. Of other affluents, the Bonito, Garças, Cristallino and Tapirapé on the west, and the Pitombas, Claro, Vermelho, Tucupá and Chavante on the east, nothing definite is known as the country is still largely unexplored. The Araguaya has a course of 1080 m., considerable stretches of which are navigable for small river steamers, but as the river below Santa Anna Island is interrupted by reefs and rapids in two places—one having a fall of 85 ft. in 18 m., and the other a fall of 50 ft. in 12 m.—it affords no practicable outlet for the products of the state. It was explored in part by Henri Coudreau in 1897.

See Coudreau’s Voyage au Tocantins-Araguaya (Paris, 1897).

ARAKAN, a division of Lower Burma. It consists of a strip of country running along the eastern seaboard of the Bay of Bengal, from the Naaf estuary, on the borders of Chittagong, to Cape Negrais. Length from northern extremity to Cape Negrais, about 400 m.; greatest breadth in the northern part, 90 m., gradually diminishing towards the south, as it is hemmed in by the Arakan Yoma mountains, until, in the extreme south, it tapers away to a narrow strip not more than 15 m. across. The coast is studded with islands, the most important of which are Cheduba, Ramree and Shahpura. The division has its headquarters at Akyab and consists of four districts—namely, Akyab, Northern Arakan Hill Tracts, Sandoway and Kyaukpyu, formerly called Ramree. Its area is 18,540 sq. m. The population at the time of the British occupation in 1826 did not exceed 100,000. In 1831 it amounted to 173,000; in 1839 to 248,000, and in 1901 to 762,102.

The principal rivers of Arakan are—(1) the Naaf estuary, in the north, which forms the boundary between the division and Chittagong; (2) the Myu river, an arm of the sea, running a course almost parallel with the coast for about 50 m.; (3) the Koladaing river, rising near the Blue mountain, in the extreme north-east, and falling into the Bay of Bengal a few miles south of the Myu river, navigable by vessels of from 300 to 400 tons burden for a distance of 40 m. inland; and (4) the Lemyu river, a considerable stream falling into the bay a few miles south of the Koladaing. Farther to the south, owing to the nearness of the range which bounds Arakan on the east, the rivers are of but little importance. These are the Talak and the Aeng, navigable by boats; and the Sandoway, the Taungup and the Gwa streams, the latter of which alone has any importance, owing to its mouth forming a good port of call or haven for vessels of from 9 to 10 ft. draught. There are several passes over the Yoma mountains, the easiest being that called the Aeng route, leading from the village of that name into Upper Burma. The staple crop of the province is rice, along with cotton, tobacco, sugar, hemp and indigo. The forests produce abundance of excellent oak and teak timber.

The natives of Arakan trace their history as far back as 2666 B.C., and give a lineal succession of 227 native princes down to modern times. According to them, their empire had at one period far wider limits, and extended over Ava, part of China, and a portion of Bengal. This extension of their empire is not, however, corroborated by known facts in history. At different times the Moguls and Pegus carried their arms into the heart of the country. The Portuguese, during the era of their greatness in Asia, gained a temporary establishment in Arakan; but in 1782 the province was finally conquered by the Burmese, from which period until its cession to the British in 1826, under the treaty of Yandaboo, its history forms part of that of Burma. The old city of Arakan, formerly the capital of the province, is situated on an inferior branch of the Koladaing river. Its remoteness from the ports and harbours of the country, combined with the extreme unhealthiness of its situation, have led to its gradual decay subsequently to the formation of the comparatively recent settlement of Akyab, which place is now the chief town of the province. The old city (now Myohaung) lies 50 m. north-east of Akyab. The Maghs, who form nearly the whole population of the province, follow the Buddhist doctrines, which are universally professed throughout Burma. The priests are selected from all classes of men, and one of their chief employments is the education of children. Instruction is consequently widely diffused, and few persons, it is said, can be found in the province who are unable to read. The qualifications for entering into the priestly order are good conduct and a fair measure of learning—such conduct at least as is good according to Buddhist tenets, and such learning as is esteemed among their votaries.

The Arakanese are of Burmese origin, but separated from the parent stock by the Arakan Yoma mountains, and they have a dialect and customs of their own. Though conquered by the Burmese, they have remained distinct from their conquerors.

The Northern Arakan Hill Tracts district is under a superintendent, who is usually a police officer, with headquarters at Paletwa. The area of the Hill Tracts is 5233 sq. m.; pop. (1901) 20,682.

(J. G. Sc.)

ARAKCHEEV, ALEKSYEI ANDREEVICH, Count (1769-1834), Russian soldier and statesman, was descended from an ancient family of Great Novgorod. From his mother, Elizabeth Vitlitsaya, he inherited most of his characteristics, an insatiable love of work, an almost pedantic love of order and the most rigorous sense of duty. In 1788 he entered the corps of noble cadets in the artillery and engineering department, where his ability, especially in mathematics, soon attracted attention. In July 1791 he was made an adjutant on the staff of Count N.I. Saltuikov, who (September 1792) recommended him to the cesarevich Paul Petrovich as the artillery officer most capable of reorganizing the army corps maintained by the prince at Gatchina. Arakcheev speedily won the entire confidence of Paul by his scrupulous zeal and undeniable technical ability. His inexorable discipline (magnified into cruelty by later legends) soon made the Gatchina corps a model for the rest of the Russian army. On the accession of Paul to the throne Arakcheev was promptly summoned to St Petersburg, appointed military commandant in the capital, and major-general in the grenadier battalion of the Preobrazhenskoe Guard. On the 12th of December 1796, he received the ribbon of St Anne and a rich estate at Gruzina in the government of Novgorod, the only substantial gift ever accepted by him during the whole of his career. At the coronation (5th of April 1797) Paul created him a baron, and he was subsequently made quartermaster-general and colonel of the whole Preobrazhenskoe Guard. It was to Arakcheev that Paul entrusted the reorganization of the army, which during the latter days of Catherine had fallen into a state of disorder and demoralization. Arakcheev remorselessly applied the iron Gatchina discipline to the whole of the imperial forces, beginning with the Guards. He soon became generally detested by the army, but pursued his course unflinchingly and introduced many indispensable hygienic reforms. “Clean barracks are healthy barracks,” was his motto. Nevertheless, the opposition of the officers proved too strong for him, and on the 18th of March 1798 he was dismissed from all his appointments. Arakcheev’s first disgrace only lasted six months. On the 11th of August he was received back into favour, speedily reinstated in all his former offices, and on the 5th of May 1799 was created a count, the emperor himself selecting the motto: “Devoted, not servile.” Five months later he was again in disgrace, the emperor dismissing him on the strength of a denunciation subsequently proved to be false. It was a fatal step on Paul’s part, for everything goes to prove that he would never have been assassinated had Arakcheev continued by his side. During the earlier years of Alexander, Arakcheev was completely overlooked. Only on the 27th of April 1803, was the count recalled to St Petersburg, and employed as inspector-general of the artillery. His wise and thorough reorganization of the whole department contributed essentially to the victories of the Russians during the Napoleonic wars. All critics agree, indeed, that the Arakcheev administration was the golden era of the Russian artillery. The activity of the inexhaustible inspector knew no bounds, and he neglected nothing which could possibly improve this arm. His principal reforms were the subdivision of the artillery divisions into separate independent units, the formation of artillery brigades, the establishment of a committee of instruction (1808), and the publishing of an Artillery Journal. At Austerlitz he had the satisfaction of witnessing the actual results of his artillery reforms. The commissariat scandals which came to light after the peace of Tilsit convinced the emperor that nothing short of the stern and incorruptible energy of Arakcheev could reach the sources of the evil, and in January 1808 he was appointed inspector-general and war minister. When, on the outbreak of the Swedish war of 1809, the emperor ordered the army to take advantage of an unusually severe frost and cross the ice of the Gulf of Finland, it was only the presence of Arakcheev that compelled an unwilling general and a semi-mutinous army to begin a campaign which ended in the conquest of Finland. On the institution of the “Imperial Council” (1st of January 1810), Arakcheev was made a member of the council of ministers and a senator, while still retaining the war office. Subsequently Alexander was alienated from him owing to the intrigues of the count’s enemies, who hated him for his severity and regarded him as a dangerous reactionary. The alienation was not, however, for long. It is true, Arakcheev took no active part in the war of 1812, but all the correspondence and despatches relating to it passed through his hands, and he was the emperor’s inseparable companion during the whole course of it. At Paris (31st of March 1814) Alexander, with his own hand, wrote the ukaz appointing him a field-marshal, but he refused the dignity, accepting, instead, a miniature portrait of his master. From this time Alexander’s confidence in Arakcheev steadily increased, and the emperor imparted to him, first of all, his many projects of reform, especially his project of military colonies, the carrying out of the details of which was committed to Arakcheev (1824). The failure of the scheme was due not to any fault of the count, but to the inefficiency and insubordination of the district officers. In Alexander’s last years Arakcheev was not merely his chief counsellor, but his dearest friend, to whom he submitted all his projects for consideration and revision. The most interesting of these projects was the plan for the emancipation of the peasantry (1818). On the accession of Nicholas I., Arakcheev, thoroughly broken in health, gradually restricted his immense sphere of activity, and on the 26th of April 1826, resigned all his offices and retired to Carlsbad. The 50,000 roubles presented to him by the emperor as a parting gift he at once handed to the Pavlovsk Institute for the education of the daughters of poor gentlemen. His last days he spent on his estate at Gruzina, carefully collecting all his memorials of Alexander, whose memory he most piously cherished. He also set aside 25,000 roubles for the author of the best biography of his imperial friend. Arakcheev died on the 21st of April 1834, with his eyes fixed to the last on the late emperor’s portrait. “I have now done everything,” he said, “so I can go and make my report to the emperor Alexander.” In 1806 he had married Natalia Khomutova, but they lived apart, and he had no children by her.

See Vasily Ratch, Memorials of Count Arakcheev (Rus.) (St Petersburg, 1864); Mikhail Ivanovich Semevsky, Count Arakcheev and the Military Colonies (Rus.) (St Petersburg, 1871); Theodor Schiemann, Gesch. Russland’s unter Kaiser Nikolaus I., vol. i., Alexander I., &c. (Berlin, 1904).

(R. N. B.)

ARAL, a lake or inland sea in the west of Asia, situated between lat. 43° 30′ and 46° 51′ N., and long. 58° 13′ and 61° 56′ E. It was known to the ancient Arab and Persian geographers as the Sea of Khwārizm or Kharezm, from the neighbouring district of the Chorasmians, and derives its present name from the Kirghiz designation of Aral-denghiz, or Sea of Islands. In virtue of its area (26,233 sq. m.) it is the fourth largest inland sea of the world. It has nearly the same length as width, namely about 170 m., if its northern gulf (Kichkineh-denghiz) is left out of account. Its depth is insignificant, the maximum being 220 ft. in a depression in the north-west, and the mean depth only 50 ft., so that notwithstanding its area it contains only eleven times as much water as the Lake of Geneva. Its altitude is 242½ ft. above the Caspian, i.e. about 155 ft. above the ocean. The lake is surrounded on the north by steppes; on the west by the rocky plateau of Ust-Urt, which separates it from the Caspian; on the south by the alluvial district of Khiva; and on the east by the Kyzyl-kum, or Red Sand Desert. On the north the shores are comparatively low, and the coast-line is broken by a number of irregular bays, of which the most important are those of Sary-chaganak and Paskevich. On the west an almost unbroken wall of rock extends from Chernychev Bay southwards, rising towards the middle to 500 ft. The southern coast is occupied by the delta of the Oxus (Jīhūn, Amu-darya), one of the arms of which, the Laudan, forms a swamp, 80 m. long and 20 broad, before it discharges into the sea. The only other tributary of any size that the sea receives is the Jaxartes (Sihun, Syr-darya) which enters towards the northern extremity of the east coast, and is suspected to be shifting its embouchure more and more to the north. This river, as well as the Amu, conveys vast quantities of sediment into the lake; the delta of the Syr-darya increased by 13¾ sq. m. between 1847 and 1900. The eastern coast is fringed with multitudes of small islands, and other islands, some of considerable size, are situated in the open towards the north and west. Kug-Aral, the largest, lies opposite the mouth of the Syr-darya, cutting off the Kichkineh-denghiz or Little Sea. The next largest island is the Nikolai, nearly in the middle. Navigation is dangerous owing to the frequency and violence of the storms, and the almost total absence of shelter. The north-east wind is the most prevalent, and sometimes blows for months together. The only other craft, except the steamships of the Russians, that venture on the waters, are the flat-bottomed boats of the Kirghiz.

In regard to the period of the formation of the Aral there were formerly two theories. According to Sir H.C. Rawlinson (Proc. Roy. Geog. Soc., March 1867) the disturbances which produced the present lake took place in the course of the middle ages; while Sir Roderick Murchison contended (Journ. of Roy. Geog. Soc., 1867, p. cxliv. &c.) that the Caspian and Aral existed as separate seas before and during all the historic period, and that the main course of the rivers Jaxartes and Oxus was determined in a prehistoric era. The former based his opinion largely on historical evidence, and the latter trusted principally to geological data. There is no doubt that in recent historical times Lake Aral had a much greater extension than it has at the present time, and that its area is now diminishing. This is, of course, due to the excess of evaporation over the amount of water supplied by its two feeders, the Amu-darya and the Syr-darya, both of which are seriously drawn upon for irrigation in all the oases they flow through. Old shore lines and other indications point to the level of the lake having once been 50 ft. above the existing level. Nevertheless the general desiccation is subject to temporary fluctuations, which appear to correspond to the periods recently suggested by Eduard Brückner (b. 1862); for, whereas the lake diminished and shrank during 1850-1880, since the latter year it has been rising again. Islands which were formerly connected with the shore are now some distance away from it and entirely surrounded by water. Moreover, on a graduated level, put down in 1874, there was a permanent rise of nearly 4 ft. by 1901. The temperature at the bottom was found (1900-1902) by Emil Berg to be 33.8° Fahr., while that of the surface varied from 44.5° to 80.5° between May and September; the mean surface temperature for July was 75°. The salinity of the water is much less than that of the ocean, containing only 1.05% of salt, and the lake freezes every year for a great distance from its shores. The opinion that Lake Aral periodically disappeared, which was for a long time countenanced by Western geographers, loses more and more probability now that it is evident that at a relatively recent period the Caspian Sea extended much farther eastward than it does now, and that Lake Aral communicated with it through the Sary-kamysh depression. The present writer is even inclined to think that, besides this southern communication with the Caspian, Lake Aral may have been, even in historical times, connected with the Mortvyi Kultuk (Tsarevich) Gulf of the Caspian, discharging part of its water into that sea through a depression of the Ust-Urt plateau, which is marked by a chain of lakes (Chumyshty, Asmantai). In this case it might have been easily confounded with a gulf of the Caspian (as by Jenkinson). That the level of Lake Aral was much higher in post-Pliocene times is proved by the discovery of shells of its characteristic species of Pecten and Mytilus in the Kara-kum Desert, 33 m. south of the lake and at an altitude of 70 ft. above its present level, and perhaps even up to 200 ft. (by Syevertsov).

The fish of Lake Aral belong to fresh-water species, and in some of its rapid tributaries the interesting Scaphirhynchus, which represents a survival from the Tertiary epoch, is found. The fishing is very productive, the fish being exported to Turkestan, Merv and Russia. The shores of the lake are uninhabited; the nearest settlements are Kazala, 55 m. east, on the Syr, and Chimbai and Kungrad in the delta of the Amu.

Authorities.—Makshéev’s “Description of Lake Aral,” and Kaulbars’ “Delta of the Amu,” in Zapiski of Russ. Geogr. Soc., 1st series, v., and new series, ix.; Grimm’s Studies of the Aral-Caspian Expedition; Nikolsky’s “Fishing in Lake Aral,” in Izvestia, Russ. Geogr. Soc., 1887; Prof. Mushketov, Turkestan, vol. i. (1886), which contains bibliographical references; Rösler, Die Aralseefrage (1873); Wood, The Shores of the Aral Lake (1876); and Berg in Izvestia, Turkestan Branch of Russian Geog. Soc. (vol. iii., Tashkent, 1902).

(P. A. K.)