Encyclopaedia Britannica [12, 9 ed.]

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t THE

ENCYCLOPAEDIA BRITANNICA A

DICTIONARY

ARTS, SCIENCES, AND GENERAL LITERATURE

NINTH EDITION

VOLUME

XII

EDINBURGH: ADAM AND CHARLES BLACK MDCCCLXXXI

[ All Bights reserved. ]

The following Articles in this volume are copyrighted in the United States of America, viz.: HOMESTEAD. HONDURAS.

Copyright, 1880, by CHARLES SCRIBNER S SONS. Copyright, 1880, by CHARLES SCRIBNER’S SONS.

BRITISH HONDURAS.

Copyright, 1880, by CHARLES SCRIBNER’S SONS.

ILLINOIS.

Copyright, 1880, by CHARLES SCRIBNER S SONS.

INDIANA.

Copyright, 1880, by CHARLES SCRIBNER S SONS.

MODERN HISTORY AND PRESENT DISTRIBUTION OF NORTH AMERICAN INDIANS.

by HENRY GANNETT. INDIAN TERRITORY.

Copyright, 1880, by HENRY GANNETT.

Copyright, 1880,

ENCYCLOPAEDIA BBITANNICA

H I R -H I R IRING, in law, may be defined as a contract by which one man grants the use of a thing to another in return for a certain price. It corresponds to the locatio-conductio of Roman law. That contract was either a letting of a thing (locatio-conductio rei) or of labour (locatio operarum). The distinguishing feature of the contract was the price. Thus the contracts of mutuum, commodatum, depositum, and mandatum, which are all gratuitous contracts, become, if a price is fixed, cases of locatio-conductio. In modern English law the term can scarcely be said to be used in a strictly technical sense. The contracts which the Roman law grouped together under the head of locatioconductio—such as those of landlord and tenant, master and servant, &c.—are not in English law treated as cases of hiring but as independent varieties of contract. Neither in law books nor in ordinary discourse could a tenant farmer be said to hire his land. Hiring would generally be applied to contracts in which the services of a man or the use of a thing are engaged for a short time. HIRSCHAU, or HIRSAIX, a village within the amt of Calw and the circle of Schwarzwald, Wiirtemberg, on the Nagold, is a station on the Pforzheim-Horb Railway, and has paper and other factories. Population 800. It owes its origin and its historical interest to the now ruinous Benedictine monastery in the neighbourhood, the Monasterium Hirsaugiense, at one period one of the most famous in Europe. It was founded in 830 or 832 by Count Erlafried of Calw, at the instigation of his son, Bishop Netting of Vercelli, who enriched it with, among other treasures, the body of St Aurelius. Its first occupants (838) were a colony of fifteen monks from Fulda, disciples of Hrabanus Maurus and Walafridus Strabus, headed by the abbot Liudebert. During about a century and a half, under the fostering care of the counts of Calw, it enjoyed great prosperity, and became an important seat of learning; but towards the end of the 10th century the ravages of the pestilence combined with the rapacity of its patrons, and the selfishness and immorality of its inmates, to bring it to the lowest ebb. After it had been desolate and in ruins for upwards of sixty years it was rebuilt in 1059, and under Abbot William “der Selige ” (1069-1091) more than regained its former splendour. By his Constitutiones Hirsaugienses, a sort of new religious order, Ordo Hirsau-

giensis, was formed, of which the rule was afterwards adopted by many monastic establishments throughout Germany, such as those of Blaubeuren, Erfurt, and Schaffhausen. The friend and correspondent of Pope Gregory VII., and of Anselm of Canterbury, he took active part in the politico-ecclesiastical controversies of his time; while a treatise from his pen, De Musica et Tonis, as well as the Thilosophicarum et astronomicarum institutionum libri III., bears witness to his interest in science and philosophy. About the end of the 12th century the material and moral welfare of Hirschau was again very perceptibly on the decline ; and it never afterwards again rose into importance. In consequence of the Reformation it was secularized in 1558 ; in 1692 it was laid in ruins by the French. The Chronicon Hirsaugiense, or, as in the later edition it is called, Annales Hirsaugienses of Trithemius (Basel, 1559 ; St Gall, 1690), is, although containing much that is merely legendary, an important source of information, not only on the affairs of this monastery, but also on the early history of Germany. The Codex Hirsaugiensis was printed at Stuttgart in 1844. See Christmann, Geschichte des Klosters Hirschau (1782); Steck, Das Kloster Hirschau (1844); Wolff, “Joh. Trithemius u. die alteste Geschichte des Klosters Hirschau,” in the Wurttembergisches Jahrbuch for 1863 ; and Helmsdorfer, Forschungen zur Geschichte des Abts Wilhelm von Hirschau (Gottingen, 1874). HIRSCHBERG, the chief town of a circle in Prussian Silesia, government district of Liegnitz, is beautifully situated at the confluence of the Bober and Zacken, and on the Silesian mountain railway, 30 miles S.W. of Lauban by rail. It is the seat of a circle court and of a chamber of commerce. A great portion of its old walls still remains, and to the south of the town there are pleasant promenades. It possesses an Evangelical church, one of the six stipulated for in the agreement between Charles of Sweden and the emperor Joseph I. in 1707; four Catholic churches, one of which dates from the 14th century; a synagogue, an Evangelical gymnasium, a school of the middle grade, a female school of the higher grade, an orphanage, and an asylum. The town is the principal emporium of commerce in the Silesian mountains, and its industries include the carding and spinning of wool, and the manufacture of linen and XII. — i

2

H I R—H

cotton fabrics, Brabant lace, veils, artificial flowers, paper, Portland cement, porcelain, sealing-wax, blacking, chemicals, machines, fire-engines, champagne, and cider 1 here is also a lively trade in corn and agricultural produce. The town is celebrated for its romantic surroundings including the Cavalierberg, from which there is a splendid view, the Hausberg, the Helicon, crowned by a small Doric temple, the Kreuzberg, with walks commanding beautiful views, and the Sattler ravine, over which there is a railway viaduct. The population in 1875 was 12,954. Hirschberg was in existence in the 11th century, and obtained town rights in 1108 from Boleslaus III. of Poland. It withstood a siege by the Hussites in 1427, and an attack of the imperial troops in 1640. The foundation of its prosperity was laid in the 16th century by the introduction of the manufacture ot linen ana vcixs. _ , HIRTIUS, AULUS, one of Csesar’s chief supporters and most intimate friends. He was with him as legatus in Gaul. After the civil war broke out in 49 B.C., he seems to have been generally stationed in Rome to protect Caesar s interests there. He was a personal friend of Cicero, and used his influence with Caesar in behalf of the orators brother and nephew. He was nominated along with Pansa by Caesar for the consulship of 43 B.C.J and after the dictator’s assassination in March 44, this honour made him for a short time one of the leading actors in that troubled time. The consuls supported the senatorial party against Antony, and led their armies into Umbria, where Antony was blockading Dec. Brutus in Mutina. On March 27th a double battle was fought: in the first Antony had the upper hand, and Pansa was mortally wounded; and in the second Hirtius completely defeated the enemy, but was himself killed in the subsequent assault on the enemy’s camp. Hirtius was perhaps an author: the eighth book of Caesar's commentaries on the Gallic war, which was certainly not written by Caesar himself, is commonly attributed to him; and the accounts of the Alexandrian, African, and Spanish wars are perhaps also due to his pen. HISPANIOLA. See HAYTI. HISSAR, a British district belonging to the division of the same name,1 in the lieutenant-governorship of the Punjab, India, lying between 28° 36' and 29° 49' N. lat., and between 75° 16' and 76° 22' E. long. It is bounded on the N. and N. W. by the Patihla state and a small portion of the British district of Slrsa, on the E. and S. by the territory of Jhind and the British district of Rohtak, and on the W. by the deserts of Bikaner. Area, 3539 square miles; population (1868), 484,681. Hiss&r forms the western border district of the great Bikaner desert, and consists for the most part of sandy plains dotted with shrub and brushwood, and broken by undulations towards the south, which rise into hills of rock like islands out of a sea of sand. The Ghaggar is its only river, whose supply is uncertain, depending much on the fall of rain in the lower Himalayas; its overflow in times of heavy rain is caught near Fatehhb&d and Murakhera by jhils, which dry up in the hot season. A canal, known as the Western Jumna Canal, crosses the district from east to west, irrigating 54 villages. The soil is in places hard and clayey, and difficult to till; but when sufficiently irrigated it is highly productive. Old mosques and other buildings exist in parts of the district. Rice is the staple crop of the district. In favourable seasons, cotton is extensively grown in lands irrigated by the Western Jumna Canal. In 1872-73, 1,431,541 acres were under tillage, out of an assessed area of 2,265,428 acres. Hiss4r produces a breed of milk-white oxen, 17 or 18 hands in height, which are in great request for the

carriages of natives. The district has always been subject to famine. The first calamity of this kind of which we have authentic record was the famine of 1783 ; since then there have been several more or less serious failures of the crops. The principal exports are oil-seeds, gram, grains, copper and brass utensils, hides, and a little cotton ; the imports —salt, sugar, fine rice, cotton goods of English make, spices, and iron. The exports are double the imports in value. The rural manufactures comprise coarse cotton cloth, vessels made of prepared skins, and copper and brass vessels. The annual out-turn of rough saltpetre is estimated at 450 maunds. The trade of the district centres in Bhaw&ni, where nine lines of traffic converge. The main road, about 50 feet wide, unmetalled, traverses the district, passing through Hdnsi and Hissdr towns ; fourteen other roads supply communication. The census of 1868 returned the population at 484,681 (males, 266,847; females, 217,834). The Hindus numbered 373,937 ; Mahometans, 102,928; Sikhs, 1812; and “ others,” 6004. There are three municipalities, viz., Bhawdni, 32,254 ; Hissdr, 14,133; and Hdnsi, 13,563. The district police numbered 396 men in 1872-73, and the municipal police 174. In the same year there were 50 schools, with 1729 scholars. The climate of Hissdr is very dry ; hot westerly winds blow from the middle of March till July. The average rainfall for the six years 1867—68 to 1872-73 was 14-57 inches. The principal diseases are fevers and smallpox. Cholera occasionally breaks out. Skin diseases also are common. Government dispensaries are situated at Bhawdni and Hdnsi. Prior to the Mahometan conquest, the semi-desert tract of which Hissar district now forms part was the retreat of Chauhan Rajputs. Towards the end of the 18th century, the Bhattis of Bhattiana gained ascendency after bloody struggles. To complete the ruin brought on by these conflicts, nature lent her aid in the great famine of 1783. Hissar passed nominally to the British in 1803, but they could not enforce order till 1810. Early in the mutiny of 1857 Hissar was wholly lost for a time to British rule, and all Europeans were either murdered or compelled to fly. The Bhattfs rose under their hereditary chiefs, and the majority of the Mahometan population followed their example. Before Delhi had been recovered, the rebels were utterly routed.

HISSAR, municipal town and administrative headquarters of the above district, 29 9 51 N. lat., 75 45 55” E. long.; population (1868), 14,133 (Hindus 9211, Mahometans 4805, Sikhs 34, Christians 83). The town is situated on the Western Jumna Canal, 102 miles W. of Delhi. It was founded in 1354 by the emperor Firoz Shdh, who constructed the canal to supply it with water; but this fell into decay during the last century, owing to the constant inroads of marauders. .Hiss&r^was almost completely depopulated during the famine of 1783, but was afterwards occupied by the adventurer George Thomas, who built a fort and collected inhabitants. It contains a cattle farm, both for commissariat purposes and for improving the breed of the province; attached is an estate of 43,287 acres for pasturage. There is an import trade in grain, ghi, sugar, oil, cotton, tobacco, and English piece goods. The municipal revenue in 1875-76 was £1229. HISSAR, a state in Central Asia, lying between the meridians of 66° 30' and 70° E. and the parallels of 39 15' and 37° N., and dependent on the amir of Bokhara. It forms that part of the basin of the Oxus which lies on the north side of the river, opposite the Afghan province of Balkh. The western prolongation of the Tian Shan, which divides the basin of the Zarafshan from that of the upper Oxus, after rising in one peak to a height of 12,300 feet, bifurcates in 67° 45' E. long. Its two arms include between them the province of Shahr-i-Sabz, with the towns 1 The division of Hissar is under a commissioner, and comprises the three districts of Hissar, Rohtak, and Sirsa. Area, 8478 square miles. of Shahr Sabz, Kitab, Yakobagh, and Karchi. The main chain and the southern arm of its bifurcation, sometimes Population (1868), 1,232,435

HIS S A R called Koh-i-tan, form the N. and N.W. boundaries of Hissar. On the W. it is wholly bounded by the desert; the Oxus limits it on the S. and S.E.; and the states of Karategin and Darwaz complete the boundary on the E. Until 1875 it was one of the least known tracts of Central Asia, but in that year a Russian expedition from Tashkend traversed and surveyed a great portion of it, and since then successive expeditions have explored various other portions, so that it is now very fairly known. Hissar is traversed from north to south by four important tributaries of the Oxus, viz., the Surkhab or Vakhsh, Kafirnihan, Surkhan, and Shirabad-Daria, which descend from the snowy mountains to the north and form a series of fertile valleys, disposed in a fan-shape, within which lie embosomed the principal towns of Hissar. The two chief roads by which Hissar is approached from Bokhara and Russian Turkestan lie through Karchi and Shahr-i-sabz respectively. Both these routes unite at Ak-roba, on the crest of the range between Khuzar and Baisun. There is also a difficult route, running through fine forests from Yakobagh across the mountains to Sarijui. A little way down the other side of the mountain chain between Khuzar and Derbend is situated the famous defile formerly called Kohluga (Mong. “ Barrier ”) and the Iron Gate, but now styled Buzghol-khana or Goat’s House. This pass is described by the Russians, who visited it and were vividly impressed with its solemnity, as a huge but narrow chasm in a transverse range, whose frowning rocks overhang and threaten to choke the tortuous and gloomy corridor (in places but 5 paces wide) affording the only exit from the valley. In ancient times it was a vantage point of much importance, and commanded the chief route between Turkestan and India. Hwen-Tsang, who passed through it in the 7th century on his way southward, states that there were then two folding doors or gates, cased with iron and hung with bells, placed across the pass. Clavijo, the Spanish ambassador to the court of Timur, heard of this when he passed through the defile 800 years after, but the gates had then disappeared. Derbend, the first inhabited place met with, is a poor village in the valley of the Shirabad-Daria, along which runs the road to the Oxus and to Afghanistan. Shirabad town itself is a place claiming great antiquity. It has a citadel and three rows of walls, and with its surrounding villages presents the aspect of a flourishing oasis. There are four ferries over the Oxus in the Shirabad chiefship or district, viz., Chushka-guzar (boar’s ferry), Patta-kissar, Shur-ab, and Karakamir. Baisun, a picturesque Uzbek town considered to be very healthy, lies on the road from Derbend to Hissar town. Emerging from the somewhat complex mountain mass which fills up this part of Hissar, the valley of the Surkhan is reached. This large river is formed by several affluents from the snowy range to the north, one of which, the Tupalan, formerly gave its name to the whole stream. The valley in its upper part is between 40 and 45 miles wide ; the banks of the river are flat and reed-grown, and are frequented by wild hogs and a few tigers. The Surkhan valley is highly cultivated, especially in its upper portion, where the villages are crowded. It supplies Bokhara with corn and sheep, but its chief products are rice and flax. When Hissar was independent the valley of the Surkhan was always its political centre, the town of Hissar being simply an outlying fortress. Passing by four fortified towns, Dehinau, Sarijui, Regar, and Karatagh, all in the basin of the Surkhan, Hissar ( = fort) claims notice. Its position at the entrance of the Pavi-dul-dul defile commanded the entrance into the fertile valleys of the Surkhan and Kafirnihan, just as Kubadian at the southern end of the latter stream defended them from the south. The

3

famous bridge of Pul-i-sanghin (stone bridge, Tash-kepri in Turkish) lies on the road from Hissar and Kafirnihan to Baljuan and Kulab. It spans the Surkhab, which is here hemmed in between lofty and precipitous cliffs barely 30 paces apart. The bridge itself abuts on projecting rocks, and is ten paces wide. The next place of importance is Kulab, in the valley of the Kichi Surkhab, so called from the lakes or inundations near which it stands. The district is part of that once famous as Khotl. The town (which, strictly speaking, is the capital of Kulab district as distinct from Hissar) contains about 500 houses and a poor citadel, and from it there are roads to Badakhshan and Kurgan-tepe and Kubadian. These two lie in the valleys of the Yaksh (or Surkhab) and Kafirnihan respectively. Kulab produces wheat in great profusion, and gold is brought thither from the surrounding districts. Kubadian is a large, silk-producing town, and is surrounded with rice-fields. Formerly the two last-named valleys were densely peopled, and a series of settlements extended southward from Dehinau, from which town an arik or canal provided the city of Termez with water. Termez, or Termedh, was an ancient and important city on the Oxus. After being destroyed by Jenghiz Khan and lying for some time in ruins, it rose again into note in the following century, and when visited by Ibn Batuta, and later by Clavijo, it had grown again into a place of some importance. It is now a mass of ruins. The population of the districts of Hissar and Kulab consists principally of Uzbeks and Tajiks, the former predominating, and, as in the valleys of the Sir and Zarafshan, gradually pushing the aboriginal Tajiks into the hills. East of Dushamba the Tajiks are the dominant race. On the banks of the Oxus there are some tribes of Baigush Turkmans who work at the ferries, drive sheep, and accompany caravans. Lyuli (gipsies), Jews, Hindus, and Afghans are also to be found in Hissar. But the Uzbeks are the most numerous, and their influence is so great that at Bokhara Hissar is known as Uzbekistan. The climate of the valleys of Hissar and Kulab is pleasant, as they are shut in by mountains to the north and open towards the Oxus to the south. Baisun (3410 feet) is the most elevated town. Hissar and Kulab produce in abundance all the cereals and garden plants indigenous to Central Asia. Cotton is grown in considerable quantities in the district of Shirabad, whence it is exported by way of Khuzar to Karshi. The difficulties of transport would prevent its being brought in any quantity from other places. Hehinau, Hissar, and Dushamba export corn and flax to Bokhara. From the vicinity of Khuzar is exported rock-salt, and sheep are brought to Bokhara and Karshi from all parts of Hissar district, as well as from Baljuan, Yurchi, and Afghanistan. A species of juniper, called archa, is used for timber. Salt is found at Bash-kurd, in the mountains of Hazret-Imam, and at other places. There are numerous brine springs in various quarters, indicating generally an inexhaustible supply of rock-salt. Auriferous sand has been discovered in the Yaksh, and the inhabitants wash the sands after the floods in spring. Merchandize is conveyed by means of camels, mules, and horses from Hissar to Karshi and Bokhara. Hot a single waggon is to be found in the district, and the wooden arba is not even known there. Politically, Hissar now consists of seven sub-districts, governed by begs, Shirabad, Baisun, Dehinau, Yurchi, Hissar, Kurgan-tepe, and Kubadian; and Kulab of two, Baljuan and Kulab. The fact of the chief route between the Russian and British possessions in Asia lying through Hissar has served of late years to bring it into prominence, and will always invest it with a certain importance. History.—Our knowledge of the history of Hissar is most fragmentary. In early written history this country was part of the Persian empire of the Acluemenkhe, and probably afterwards of the Graeco-Bactrian kingdom, and then subject to the Eastern swarms who broke this up. In the time of the Sassanian kings of Persia it was under the Haiathalah, the Ephthalites or White Huns of the Greeks, subdued by the Turks in the early part of the 7th century, these soon to be displaced by the Mahometan power. Termedh, Kubadian, and Chagaman are named as places of importance by the Arab geographers of the 10th century ; the last name was also applied territorially to a great part of the Hissar province, but is now obsolete. The country was successively subject to the Mongol Chagatai dynasty and to Timur and his successors ; it afterwards became a' cluster of Uzbek states of obscure history. Hissar was annexed by the amir of Bokhara in 1869-70, soon after the Russian occupation of Samarcand. (C. E. D. B.)

4

HISTOLOGY

A

I.

ANIMAL HISTOLOGY.

NIMAL HISTOLOGY (from m-ros, a web or tissue, and Adyos, discourse) is the study of the minute structure of the tissues of animals. By a tissue is meant any part of an organism which has undergone special changes in structure in adaptation to the performance of special functions. These special changes are expressed by the general term “differentiation.” In the lowest animal organisms, the whole of whose bodies are composed of the undifferentiated living substance termed “protoplasm,” we find all its functions shared by every part of the organism. An amoeba, for example, it is well known, is capable of finding, seizing, devouring, digesting, and assimilating food, has a special provision for collecting fluid and pumping it out of its body, respires by its whole surface, moves about apparently where it will, exhibits a sensibility to tactile impressions, and reacts in all probability to smell if not to sound and light,—in short, is capable of performing, although with the lowest possible amount of activity, almost every function which animals vastly higher in the scale of organization exhibit. But even in the amoeba we cannot say certainly that there is no differentiation of its protoplasm. For a condensed portion—tne nucleus—is set aside to initiate the reproductive function, and it is by means of the external and firmer layer (ectoplasm) that its movements are effected and its relations with the external world maintained, while the internal more fluid protoplasm (endoplasm) is concerned with the digestion of the food. Still there are simple organisms whose protoplasm is probably absolutely undifferentiated. On the other hand, there are other organisms which are also regarded as composed of simple protoplasm, and are constituted by a single cell, which nevertheless show a marked progress in the differentiation of portions of their substance apart altogether from the presence of a nucleus. Such differentiation in unicellular organisms generally takes the form of the production of a shell or “ test,” as in the Foraminifera and in Noctiluca, which subserves purely passive functions of sustentation or defence. It is not certain in such cases whether the structure thus produced is formed by the direct conversion of the protoplasm or by an exudation on the surface which subsequently hardens. But portions of the protoplasm may be set aside for the performance of active functions. We see this in its production in the form of locomotory organs, either temporary (pseudopodia) or permanent (cilia). But in neither of these can any actual change in the minute structure of the protoplasm be observed. A differentiation does, however, occur in one remarkable instance—the flagellum, namely, of the Noctilucidce (fig. 1), which exhibits as definite a transverse striation as does the cross-striated or voluntary muscular tissue of the higher animals, in which structural peculiarity it is impossible not to infer a relation to its contractile functions • and similarly, in the Vorticellidce, there is a differentiation of the protoplasm of the rapidly contractile stalk. Whereas in the more highly organized unicellular animals portions of the single cell are thus set aside for the performance of special functions, and modified in structure accordingly, in multicellular animals, on the other hand, we find whole cells and sets of cells set apart and differentiated. It is to such modifications in sets of cells in multicellular organisms, rather than in portions of the protoplasm of a unicellular organism, that “ histological differentiation ” is commonly restricted; and each such set of cells, destined for the performance of a special function, and modified accordingly in structure, is denominated a “tissue.”

The animal tissues may be classed under the four heads of Epithelium, Connective Tissue, Muscular Tissue, and Nervous Tissue.1 Of these four classes of tissue the epithelium is the most primitive and least altered. In the development of the Metazoa the numerous embryonic cells which result from the division of the single cell—the ovum —tend in nearly every case to arrange themselves as a single layer surrounding a central cavity (unilaminar condition of the blastoderm), (fig. 2, A).2 Presently a part of the wall of the hollow sphere becomes invaginated, so that, instead of a vesicle enclosed by but a single layer of cells, a cup {Gastrula, Haeckel), is produced (fig. 2, B), the wall of which is formed by two layers derived from the original single layer, and separated from one another by a narrow interval (which is all that remains of the original cavity of the vesicle) except at the orifice of the cup, where they are continuous (bilaminar condition of the blastoderm). At this part some cells become separated from one or both of

Fig. 1.

Fig. 2.

1.—Flagellum of Noctihica miliaris (highly magnified). transversely striated substance ; b, base of attachment to body of animal. FIG. 2.—Sections through the unilaminar (A), bilaminar (B), and trilaminar (C) conditions of the typical blastoderm. Ect., ectoderm; Ant., entoderm; Mes., mesoderm; c, primitive connective tissue. FIG.

these two primary layers, and, extending in and occupying the cleft-like space which separates them, become a third layer of cells, which differs from those of the other two in not being arranged into a continuous membrane, and not, therefore, forming an epithelium (trilaminar condition of the blastoderm), (fig. 2, C). Now, of these three layers, the outer one, or ectoderm, and the inner one, or entoderm, give rise to all the epithelial tissues of the body. The nervous tissues are also derived from the ectoderm; whereas the connective and muscular tissues originate in the mesoderm or middle layer. In most of the Coelenterata, however, the mesoderm is not developed at one part only of the embryo as in the higher Metazoa. In the hydroid polyps and Medusae it never becomes completely distinct from the ectoderm and entoderm, although a jelly-like sustentacular substance may be formed to a greater or less extent between the two primary layers, and cells may pass into it from one of them, so that a kind of mesoderm is thus produced. In the Medusae, also, the muscular function is performed by 1 The characters of the several tissues and their varieties are best known as they occur in the Yertebrata, and a description of them will be found in the article on ANATOMY. 2 A layer of cells which thus forms a membrane by the union of the cells, with an imperceptible amount of intercellular cementing substance, would properly fall under the definition of the term epithelium, which was first applied by Ruysch to the cellular membrane covering the lips, and has ever since been used to designate membranes thus I composed of cells alone.

HISTOLOGY

ANIMAL.]

cells which either still have their place in the general layer of the ectoderm or are but imperfectly separated from it; and here, again, the commencing separation does not occur at one part only, but over extensive tracts of the surface. Nevertheless these cells are modified in structure precisely in the same way as those which in higher animals are derived from the mesoderm. The nervous functions are also performed by cells and fibres, which, although they show those modifications of structure which in the higher animals are characteristic of nervous tissue, yet remain strictly confined to the ectoderm, and do not, as in the higher animals, penetrate into the mesoderm. The Epithelial Tissues.—Although, as we have seen (see p. 4, note 2), the layers of cells which are first formed are layers of epithelium, and, therefore, the epithelial tissues are the first to be produced, nevertheless we find that they undergo less modification in structure than any of the other three classes of tissue. As before said, they invariably consist merely of cells cemented together by an imperceptible amount of intercellular substance,1 and the cells themselves only show minor degrees of modification in shape and structure, at least as compared with the other tissues constituted mainly of cells, namely, the muscular and nervous. Modifications in Shape of Epithelial Cells.—The cells of this tissue may be either elongated and set like palisades over the surface which they cover, in which case they are termed “ columnar ” (fig. 3), or they may be flattened out over the surface, and they then appear as thin “scales”; and every variation in shape is met with between these two extremes. In any case where they form a single layer, since the cells are set closely together, the mutual apposition of neighbouring cells produces a flattening of the opposed sides, so that, when the epithelium is looked at from the surface, the cells have a polygonal outline, and collectively present the appearance of a mosaic pavement (fig. 4). In

Fig. 3.

Fig. 4. FIG. FIG. FIG.

Fig. 5.

3.—Columnar epithelium cells. 4.—Mosaic appearance of epithelium. 5.—Stratified epithelium.

certain cases, especially where there is liability to abrasion of the surface which they cover, the epithelial cells are disposed in two, three, or more superimposed layers (fig. 5), and then the cells of the different layers may vary much in size, shape, and consistence. Such an epithelium is termed “stratified.” It frequently happens that the layer of epithelium which covers a surface is prolonged into depressions, which may be quite simple or may be ramified either slightly or in the most complex manner. The epithelial cells which line such depressions may resemble those of the surface upon which the depression opens, or they may become more or less modified in size, shape, and other particulars, and constitute themselves into a distinct variety of epithelial tissue. Since depressions like those just mentioned are generally for the purpose of forming some special secretion,and are termed glands, and since this secretion is elaborated by the agency of the epithelial cells which line the gland, any such special 1 Exceptions to this general rule are seen in the layer of cells which underlies the chitinous cuticula of annelids (Claparede), and in the enamel organ of the developing teeth of vertebrates (Kolliker), where the cells, although epithelial, are ramified and united by their branches into a network; and, in a far less degree, in many of the lower cells of a stratified epithelium, where it can be seen with a high power that the edges and surfaces of the cells are provided with numerous short projections which are applied to those on adjacent cells.

o

variety of epithelium is termed a “glandular” or “secreting” epithelium. Modifications in Structure.—The modifications in structure which the cells of epithelial tissue undergo are comparatively slight. One of the most common is the conversion of the external layer of the protoplasm of the cell into a firm membrane, generally of a horny nature, but this membrane is seldom sharply marked off from the substance of the cell, as is the case with the cellulose membrane of the vegetable cell. It becomes formed, moreover, to a very different extent in different cells, according to the function which the particular epithelium has to perform; where, for example, the epithelium is almost purely a protective covering, as in the stratified scaly epithelia, a considerable part, or even the whole thickness of many of the epithelial cells, is thus transformed ; but where, on the other hand, the cells have to play an active part in yielding a secretion to moisten the surface, or in protruding a portion of their protoplasm in the form of vibratile cilia to produce currents over the surface, or to move the organism through the water, we find little, if any, of such conversion of the superficial cell-substance. What little there may be is confined to the attached surfaces of the cell, or if there is any such covering on the free surface, it is penetrated by pores which allow of a communication between the protoplasm of the cell and the external medium. Another common modification of structure which epithelial cells exhibit is the existence of vibratile cilia at the free surface (fig. 6). This, again, is especially frequent with cells of a columnar shape, but it may occur in any. The cilia appear to be protrusions of the more active external protoplasm of the cell, which are in most cases incapable of being again withdrawn, and are in all probability modified in minute structure, although they are always so small that such modification, if it exists, escapes detection even with the employment of the highest powers of the microscope. At their base, however, the cilia are certainly continuous with the unaltered protoplasm of the cell. This may be |

II

Fig. 6.

Fig. 7. FIG. FIG. FIG. FIG.

Fig. 8.

Fig. 9.

6.—A ciliated epithelium cell. 7.—A striated epithelium cell. 8.—A ciliated cell with one large cilium. 9.—Sense-epithelium cell of Aurelia.

seen even where the cilia are small and spring in a bunch from the free surface of the cell, but much better in those kinds of ciliated epithelium in which but a single large cilium is connected to each columnar cell (fig. 8). Many epithelial cells, especially those of secreting glands, show a differentiation of their protoplasm in the form of fine striae or rods which pass from the attached border of the cell towards the free end (fig. 7). Cells thus modified are found in the ducts of the salivary glands, in the alveoli of the pancreas, and in the convoluted tubules of the kidney in Yertebrata. One of the most remarkable modifications which epithelium cells exhibit is found in the organs of special sense. This is the presence of a fine filamentous process or processes springing from the free surface of the epithelium cells, and resembling in their appearance long cilia, but not spontaneously vibratile (fig. 9). Moreover, the cells in question,

6

HISTOLOGY

which are generally of an elongated columnar form, commonly branch out at their detached end into fine processes which appear to become connected with nerve-fibres. Cells of this character occur even so low in the Metazoa as the Medusa;, in connexion with the nerve-epithelium to be afterwards mentioned. And, indeed, in many cases where cells of this character enter into the constitution of the sense organs, it is probably most consistent with their true nature to regard them as detached portions of neivous tissue, which also in every case is originally of an epithelial nature. Modifications in the Cell Contents.—Another chief modification which the cells of an epithelial tissue may undergo consists in the accumulation within the cells of various chemical substances, which may be either taken in bodily as such, or may be formed in the cell from other substances which are supplied to it by the blood. The substances that are thus accumulated and formed within the cells of an epithelium are of very various nature, as, for example, the constituents of special secre- ^ tions (fig. 10), mucin, pigment, ^•^oTgano^mrfiusfconfatty globules, uric acid, &C., &C. taining crystals of uric acid. These several substances are toler- (Boll) ably constant in an epithelium of the same kind thus, mucin is a very frequent constituent of columnar epithelium, and in glands which have the same function in different animals, the same substances are found in the epithelium cells of the gland. Exudation from Epithelium Cells. Formation of Cuticular Structures.—In many invertebrates the epithelium which covers the surface of the body, and sometimes also that which lines a part of the alimentary canal, forms an exudation which is generally soft at first, but may afterwards harden into a horny consistency, or may be rendered still harder and at the same time more brittle by impregnation with earthy salts. Any such structure is termed a cuticular formation, It may be composed of a single thin layer, or a number of layers may be superimposed, so that a “ shell ” of considerable thickness is thus formed. The chitinous or calcareous covering which forms the exoskeleton in many molluscs, arthropods, annelids, and Ilydrozoa is of this nature. On the other hand, the firm skeletons of sponges, Actinozoa, and Echinodermata are formed by deposition in the connective tissue. The Connective Tissues.—The connective tissues are characterized by the great development of intercellular substance in comparison with the cells ; indeed in those animals in which connective tissue may first of all be said to appear, there is an entire absence of cellular elements properly belonging to the tissue. This is the case in many of the Ccelenterata, in which the connective tissue is represented merely by a layer, more or less thick, of hyaline substance, which undoubtedly performs a sustentacular function, in addition to connecting together the epithelial layers of the ectoderm and entoderm. The intercellular or ground substance almost invariably takes a prominent part in the formation of connective tissue. It is of a semi-fluid nature, and often contains in addition to albumen a certain amount of mucin. In most cases the cells of the connective tissue separate themselves from the primary layers before the formation of this ground substance ; indeed the mesoderm is at first chiefly formed of these cells. The stages of development are as follows. The mesodermic cells, which are at first in apposition, become separated from one another by the accumulation of intercellular substance, but at the same time maintain a connexion with one another throughout the tissue by

[ANIMAL.

their branching cell-processes (see fig. 2, C, c). Presently, in the production of ordinary connective tissue, fibres of two kinds make their appearance in the intercellular substance, and to all appearance independent of the cells. Those of the one kind (fig. 11, A) are highly elastic and refracting, not easily affected by reagents, stain deeply with magenta, run singly, always branch, and become united with neighbouring fibres so as to form a network throughout the tissue; those of the other kind A (fig. 11, B) are excessively fine and indistinct, never run singly Fig. Hbut always in bundles, and generally with a wavy course, are readily affected by reagents, and, in vertebrates, yield gelatin on boiling. In the various kinds of connective tissue the relative proportion of these two kinds of fibres to one another and to the cellular elements of the tissue varies. Thus in the so-called elastic tissue of the Yertebrata the elastic fibres greatly preponderate; in tendinous tissue, on the other hand, they are scarcely to be found, and the ground is almost wholly occupied by the white fibres. It may happen that the intercellular substance is so completely occupied by the fibres as to be entirely obscured, but its presence may be always recognized in consequence of the property which it possesses of reducing silver from its salts when exposed to the light. In certain cases the intercellular substance becomes hardened by the deposit within it either of a substance termed chondrin, which confers upon it the well-known toughness and elasticity of cartilage, or by a deposit of earthy salts imparting to it the firmness of bone. These several changes in the intercellular substance are accompanied by special modifications in the form and relations of the cells (by whose agency they are in all probability effected). In comparatively rare cases the intercellular substance which is found occupying the meshes of the network formed by the branched cells of the developing connective tissue may disappear entirely, and the meshes may be occupied either by blood or by the lymph or plasma of the blood (spleen and lymphatic glands of vertebrates). It frequently happens that the connective tissue presents the consistence of jelly, and this is generally ascribed to the characters of the intercellular substance. It may, however, be due in many cases to the entanglement of fluid in the meshes of the fibres, and not to a gelatinization of the ground substance. This is shown by the fact that the fluid may be drained from out the meshes by means of filter paper. And the possibility of the formation of a jelly in this manner is evidenced in the coagulation of lymph, where the apparently solid gelatinous clot is a tangled meshwork of fine filaments enclosing fluid. The connective tissues of invertebrates are, on the whole, similar to those of the vertebrate) at the same time it must be admitted that there are not unimportant differences in chemical constitution, such as the absence of a substance yielding gelatin, and the absence for the most part of mucin, both of which are characteristic constituents of vertebrate connective tissue. On the other hand the anatomical characters of the elements, both cells and fibres, are in most cases sufficiently well marked to be recognizable. In the sponges the bulk of the animal is made up of a jelly which, when examined under the microscope, is found

HISTOLOGY

ANIMAL.]

to consist of large branched cells (fig. 12) connected together by their processes into a network. The meshes of this are occupied by clear intercellular substance within which the calcareous or horny matter which forms the skeleton is deposited.

FIG.

12.—Connective tissue of sponge. (F. E. Schulze.)

When the development of the sponge is traced it is found that the first part of the tissue to be seen is the clear intermediate substance, and the skeletal spicules begin to appear in this before the cellular elements. These wander subsequently into it from one of the primary layers. There can be no doubt that this jelly-like tissue of the sponge represents a primitive form of connective tissue, although, so far as has at present been ascertained, no fibres are developed in it. In the Coelenterata, as in the sponges, the connective tissue makes its first appearance in the form of a clear intermediate substance, which may be so small in amount as to be almost imperceptible, or so large in amount as to form the main bulk of the organism. In the former case, as in the developing sponge, there is an entire absence of both fibres and cells, whereas in the latter case both kinds of elements are found. The fibres are the more constant, and are of the elastic kind (fig. 13); they have for the most part a direction across the thickness of the tissue stretching from entoderm to ectoderm, branching and uniting with their neighbours to form the characteristic network which, enclosing watery fluid in its meshes, FIG. 13.—Cells and elastic fibres from connective tissue of Aurtlia. produces the jelly-like consistence of the tissue. Fibres of the white variety are also found as low down in the Metazoa as the Goelenterata. In some of the acraspedote Medusas they occur in the form of bundles of indistinct wavy fibres situated near the surface of the jelly, and in the Actiniae similar fibres are found forming membranes which bear a strong resemblance to some of the forms of membranous connective tissue of the Yertebrata (fig. 14). As before

FIG.

14.—Fibres and cells of connective tissue of an Actinia.

7

surprising, therefore, to find in all the higher classes of the Invertebrata that similar elements characterize the connective tissue, although there are undoubtedly certain modifications and exceptions. The most noteworthy modifications occur in the chemical constitution of the ground substance and of the fibres. Thus, as before mentioned, there is for the most part an absence of the gelatin-yielding substance of the vertebrate connective tissue. On the other hand, the intercellular substance may become infiltrated with chemical principles unknown in vertebrate histology, as in the tunic of the Tunicata, where cellulose is found.1 There are modifications also in the appearance of the connective tissue fibres which are often accompanied by modifications in the chemical constitution. For example, in the Arihropoda the tissue often undergoes extensive chitinization, and the fibres in it present a straight, stiff appearance, very unlike the soft, wavy look which is exhibited by the fibrous tissue of the Vertebrata. Although the ramified cell may be looked upon as on the whole the most characteristic form of cell met with in connective tissue, and although this is the first modification in shape which the rounded embryonic cells of the developing vertebrate connective tissue take on, nevertheless it gives place in many parts both in invertebrates as well as vertebrates to other forms. One of the commonest of these is the flat cell, and we almost invariably find cells of this description lying on or in connective tissue membranes, and lining cavities which may have become formed in the connective tissue. In the latter case the flat cells may be and most commonly are spread over the whole inner surface of the cavity which they line, and assume the appearance of a pavement epithelium. Such cells, which are termed epithelioid (or by some endothelial), are found lining the body cavity and the vascular canals and heart (where these exist) of all invertebrates just as they do the similar cavities and canals in vertebrates, and they are derived like the rest of the cells of the connective tissue from the mesoderm, and therefore only indirectly from the primary blastodermic layers. But in the holothurians, and some other animals, the cells in question are derived directly from the entoderm. In the Mollusca (fig 15) a peculiar type of connective tissue cell makes its appearance in addition to the rounded, the ramified, and the flattened forms. This takes the

(Kolliker.)

mentioned, in the lower forms of Codenterata cells are entirely absent from their jelly-like connective tissue, but in the higher forms scattered cells (fig. 13) of indeterminate shape and position, but generally in the neighbourhood of the entoderm, begin to make their appearance. Some of these cells are amoeboid, but others become fixed, and arranged in a network which pervades the jelly. We see then that the cells, the intercellular substance, the white fibres, and the elastic fibres of the vertebrate connective tissue are represented in these low forms of the Metazoa in a perfectly recognizable manner. It is not

FIG.

15.—Connective tissue of slug, r, ramified cell; /, flattened cell; i\ vesicular cell. The fibres in the ground substance are also indicated.

shape of a large clear, vesicular, double-contoured cell-body (y) with a relatively small nucleus. Cells of this character are in some cases only to be found scattered here and there in the tissues, but in others they are closely collected masses, and by their aggregation confer an almost cartilaginous consistency upon the tissue. This is 1 This tunic seems, however, from its development to be an epithelial structure, although resembling in many respects Connective tissue.

8

HISTOLOGY

not due, however, to the accumulation of chondrin the chemical principle of the cartilage of vertebrates—-in intercellular substance. But a true cartilage is met with in some of the higher molluscs (Cephalopoda)t in which there is a considerable amount of intercellular substance, and the only difference, as compared with ordinary cartilage of most vertebrates, is that the cells are much ramified (as in some fishes). Bone, or osseous connective tissue, as the word is understood in vertebrate histology, is not met with anywhere amongst the Invertebrate, and this is less to be wondered at since it does not make its appearance even in some of the lowest of the Yertebrata. But hard structures of various kinds serve to supply the place of bone as a sustentacular tissue, and these may be developed either within the connective tissue, so as to form an internal hard skeleton, or on the exterior of the body, so as to form an external skeleton or shell. When external the shell is an epithelial structure, or at least is produced by the formative activity of the epithelium which covers the surface of the body. An internal hard skeleton may either coexist with an external, or the one may be found to the exclusion of the other. In the coelenterates the internal skeleton when found is generally deposited in the jelly-like intercellular substance in the form of separate spicules, which subsequently are cemented together by a further deposit of calcareous matter into a continuous skeleton. In the sponges the calcareous spicules often project fromthe jelly into theexternalmedium, but it is probable that they are covered by an extension of the superficial flattened cells which they seem to piercej the separate calcareous spicules are in some cases united by calcareous matter, in others by horny substance, or the spicules may be altogether absent and the horny framework constitute the whole skeleton. There is no evidence to show that these calcareous and $ horny deposits are formed by the acid. (Leydig.) The connective direct agency of the cells ol the jgfj.. some are cut transversely; iellv-like tissue, On, the . conon the right they are obscured J J . by the calcareous globules O'), trary, the tact that the spicules Above and below is seen a layer make their appearance in the of epithelium (e,