Chapter III: Relations Between Crystalline Form and Chemical Composition (1)

That the general and physical characters of a chemical substance are profoundly modified by crystalline structure is strikingly illustrated by the two crystalline modifications of the element carbon--namely, diamond and graphite. The former crystallizes in the cubic system, possesses four directions of perfect cleavage, is extremely hard and transparent, is a non-conductor of heat and electricity, and has a specific gravity of 3.5; whilst graphite crystallizes in the hexagonal system, cleaves in a single direction, is very soft and opaque, is a good conductor of heat and electricity, and has a specific gravity of 2.2. Such substances, which are identical in chemical composition, but different in crystalline form and consequently in their physical properties, are said to be "dimorphous." Numerous examples of dimorphous substances are known; for instance, calcium carbonate occurs in nature either as calcite or as aragonite, the former being rhombohedral and the latter orthorhombic; mercuric iodide crystallizes from solution as red tetragonal crystals, and by sublimation as yellow orthorhombic crystals. Some substances crystallize in three different modifications, and these are said to be "trimorphous"; for example, titanium dioxide is met with as the minerals rutile, anatase and brookite (q.v.). In general, or in cases where more than three crystalline modifications are known (e.g. in sulphur no less than six have been described), the term "polymorphism" is applied.

On the other hand, substances which are chemically quite distinct may exhibit similarity of crystalline form. For example, the minerals iodyrite (AgI), greenockite (CdS), and zincite (ZnO) are practically identical in crystalline form; calcite (CaCO3) and sodium nitrate (NaNO3); celestite (SrSO)4 and marcasite (FeS2); epidote and azurite; and many others, some of which are no doubt only accidental coincidences. Such substances are said to be "homoeomorphous" (Gr. [Greek: homoios], like, and [Greek: morphe], form).

Similarity of crystalline form in substances which are chemically related is frequently met with and is a relation of much importance: such substances are described as being "isomorphous." Amongst minerals there are many examples of isomorphous groups, e.g. the rhombohedral carbonates, garnet (q.v.), plagioclase (q.v.); and amongst crystals of artificially prepared salts isomorphism is equally common, e.g. the sulphates and selenates of potassium, rubidium and caesium. The rhombohedral carbonates have the general formula R"CO3, where R" represents calcium, magnesium, iron, manganese, zinc, cobalt or lead, and the different minerals (calcite, ankerite, magnesite, chalybite, rhodochrosite and calamine (q.v.)) of the group are not only similar in crystalline form, cleavage, optical and other characters, but the angles between corresponding faces do not differ by more than 1 deg. or 2 deg. Further, equivalent amounts of the different chemical elements represented by R" are mutually replaceable, and two or more of these elements may be present together in the same crystal, which is then spoken of as a "mixed crystal" or isomorphous mixture.

In another isomorphous series of carbonates with the same general formula R"CO3, where R" represents calcium, strontium, barium, lead or zinc, the crystals are orthorhombic in form, and are thus dimorphous with those of the previous group (e.g. calcite and aragonite, the other members being only represented by isomorphous replacements). Such a relation is known as "isodimorphism." An even better example of this is presented by the arsenic and antimony trioxides, each of which occurs as two distinct minerals:--

As2O3, Arsenolite (cubic); Claudetite (monoclinic).
Sb2O3, Senarmontite (cubic); Valentinite (orthorhombic).

Claudetite and valentinite though crystallizing in different systems have the same cleavages and very nearly the same angles, and are strictly isomorphous.

Substances which form isodimorphous groups also frequently crystallize as double salts. For instance, amongst the carbonates quoted above are the minerals dolomite (CaMg(CO3)2) and barytocalcite (CaBa(CO3)2). Crystals of barytocalcite (q.v.) are monoclinic; and those of dolomite (q.v.), though closely related to calcite in angles and cleavage, possess a different degree of symmetry, and the specific gravity is not such as would result by a simple isomorphous mixture of the two carbonates. A similar case is presented by artificial crystals of silver nitrate and potassium nitrate. Somewhat analogous to double salts are the molecular compounds formed by the introduction of "water of crystallization," "alcohol of crystallization," &c. Thus sodium sulphate may crystallize alone or with either seven or ten molecules of water, giving rise to three crystallographically distinct substances.

A relation of another kind is the alteration in crystalline form resulting from the replacement in the chemical molecule of one or more atoms by atoms or radicles of a different kind. This is known as a "morphotropic" relation (Gr. [Greek: morphe], form, [Greek: tropos], habit). Thus when some of the hydrogen atoms of benzene are replaced by (OH) and (NO2) groups the orthorhombic system of crystallization remains the same as before, and the crystallographic axis a is not much affected, but the axis c varies considerably:--

a : b : c
Benzene, C6H6 0.891 : 1 : 0.799
Resorcin, C6H4(OH)2 0.910 : 1 : 0.540
Picric acid, C6H2(OH)(NO2)3 0.937 : 1 : 0.974

A striking example of morphotropy is shown by the humite (q.v.) group of minerals: successive additions of the group Mg2SiO4 to the molecule produce successive increases in the length of the vertical crystallographic axis.

In some instances the replacement of one atom by another produces little or no influence on the crystalline form; this happens in complex molecules of high molecular weight, the "mass effect" of which has a controlling influence on the isomorphism. An example of this is seen in the replacement of sodium or potassium by lead in the alunite (q.v.) group of minerals, or again in such a complex mineral as tourmaline, which, though varying widely in chemical composition, exhibits no variation in crystalline form.

For the purpose of comparing the crystalline forms of isomorphous and morphotropic substances it is usual to quote the angles or the axial ratios of the crystal, as in the table of benzene derivatives quoted above. A more accurate comparison is, however, given by the "topic axes," which are calculated from the axial ratios and the molecular volume; they express the relative distances apart of the crystal molecules in the axial directions.

The two isomerides of substances, such as tartaric acid, which in solution rotate the plane of polarized light either to the right or to the left, crystallize in related but enantiomorphous forms.

REFERENCES.--An introduction to crystallography is given in most
text-books of mineralogy, e.g. those of H. A. Miers and of E. S. Dana
(see MINERALOGY). The standard work treating of the subject generally
is that of P. Groth, _Physikalische Kristallographie_ (4th ed.,
Leipzig, 1905). A condensed summary is given by A. J. Moses, _The
Characters of Crystals_ (New York, 1899).

For geometrical crystallography, dealing exclusively with the external
form of crystals, reference may be made to N. Story-Maskelyne,
_Crystallography, a Treatise on the Morphology of Crystals_ (Oxford,
1895) and W. J. Lewis, _A Treatise on Crystallography_ (Cambridge,
1899). Theories of crystal structure are discussed by L. Sohncke,
_Entwickelung einer Theorie der Krystallstruktur_ (Leipzig, 1879); A.
Schoenflies, _Krystallsysteme und Krystallstructur_ (Leipzig, 1891);
and H. Hilton, _Mathematical Crystallography and the Theory of Groups
of Movements_ (Oxford, 1903).

The physical properties of crystals are treated by T. Liebisch,
_Physikalische Krystallographie_ (Leipzig, 1891), and in a more
elementary form in his _Grundriss der physikalischen Krystallographie_
(Leipzig, 1896); E. Mallard, _Traite de cristallographie,
Cristallographie physique_ (Paris, 1884); C. Soret, _Elements de
cristallographie physique_ (Geneva and Paris, 1893).

For an account of the relations between crystalline form and chemical
composition, see A. Arzruni, _Physikalische Chemie der Krystalle_
(Braunschweig, 1893); A. Fock, _An Introduction to Chemical
Crystallography_, translated by W. J. Pope (Oxford, 1895); P. Groth,
_An Introduction to Chemical Crystallography_, translated by H.
Marshall (London, 1906); A. E. H. Tutton, _Crystalline Structure and
Chemical Constitution_, 1910. Descriptive works giving the
crystallographic constants of different substances are C. F.
Rammelsberg, _Handbuch der krystallographisch-physikalischen Chemie_
(Leipzig, 1881-1882); P. Groth, _Chemische Krystallographie_ (Leipzig,
1906); and of minerals the treatises of J. D. Dana and C. Hintze.
(L. J. S.)

FOOTNOTES:

[1] From the Greek letter [delta], [Delta]; in general, a
triangular-shaped object; also an alternative name for a trapezoid.

[2] Named after pyrites, which crystallizes in a typical form of this
class.

[3] From [Greek: plagios], placed sideways, referring to the absence
of planes and centre of symmetry.

[4] From [Greek: gyros], a ring or spiral, and [Greek: eidos], form.

[5] From [Greek: monos], single, and [Greek: klinein], to incline,
since one axis is inclined to the plane of the other two axes, which
are at right angles.

CRYSTAL PALACE, THE, a well-known English resort, standing high up in grounds just outside the southern boundary of the county of London, in the neighbourhood of Sydenham. The building, chiefly of iron and glass, is flanked by two towers and is visible from far over the metropolis. It measures 1608 ft. in length by 384 ft. across the transepts, and was opened in its present site in 1854. The materials, however, were mainly those of the hall set up in Hyde Park for the Great Exhibition of 1851. The designer was Sir Joseph Paxton. In the palace there are various permanent exhibitions, while special exhibitions are held from time to time, also concerts, winter pantomimes and other entertainments. In the extensive grounds there is accommodation for all kinds of games: the final tie of the Association Football Cup and other important football matches are played here, and there are also displays of fireworks and other attractions.

CSENGERY, ANTON (1822-1880), Hungarian publicist, and a historical writer of great influence on his time, was born at Nagyvarad on the 2nd of June 1822. He took, at an early date, a very active part in the literary and political movements immediately preceding the Hungarian Revolution of 1848. He and Baron Sigismund Kemeny may be considered as the two founders of high-class Magyar journalism. After 1867 the greatest of modern Hungarian statesmen, Francis Deak, attached Csengery to his personal service, and many of the momentous state documents inspired or suggested by Deak were drawn up by Csengery. In that manner his influence, as represented by the text of many a statute regulating the relations between Austria and Hungary, is one of an abiding character. As a historical writer he excelled chiefly in brilliant and thoughtful essays on the leading political personalities of his time, such as Paul Nagy, Bertalan, Szemere and others. He also commenced a translation of Macaulay's _History_. He died at Budapest on the 13th of July 1880.

CSIKY, GREGOR (1842-1891), Hungarian dramatist, was born on the 8th of December 1842 at Pankota, in the county of Arad. He studied Roman Catholic theology at Pest and Vienna, and was professor in the Priests' College at Temesvar from 1870 to 1878. In the latter year, however, he joined the Evangelical Church, and took up literature. Beginning with novels and works on ecclesiastical history, which met with some recognition, he ultimately devoted himself to writing for the stage. Here his success was immediate. In his _Az ellenallhatatlan_ ("L'Irresistible"), which obtained a prize from the Hungarian Academy, he showed the distinctive features of his talent--directness, freshness, realistic vigour, and highly individual style. In rapid succession he enriched Magyar literature with realistic _genre_-pictures, such as _A Proletarok_ ("Proletariate"), _Buborckok_ ("Bubbles"), _Ket szerelem_ ("Two Loves"), _A szegyenlos_ ("The Bashful"), _Athalia_, &c., in all of which he seized on one or another feature or type of modern life, dramatizing it with unusual intensity, qualified by chaste and well-balanced diction. Of the latter, his classical studies may, no doubt, be taken as the inspiration, and his translation of Sophocles and Plautus will long rank with the most successful of Magyar translations of the ancient classics. Among the best known of his novels are _Arnold_, _Az Atlasz csalad_ ("The Atlas Family"). He died at Budapest on the 19th of November 1891.

CSOKONAI, MIHALY VITEZ (1773-1805), Hungarian poet, was born at Debreczen in 1773. Having been educated in his native town, he was appointed while still very young to the professorship of poetry there; but soon after he was deprived of the post on account of the immorality of his conduct. The remaining twelve years of his short life were passed in almost constant wretchedness, and he died in his native town, and in his mother's house, when only thirty-one years of age. Csokonai was a genial and original poet with something of the lyrical fire of Petofi, and wrote a mock-heroic poem called _Dorottya or the Triumph of the Ladies at the Carnival_, two or three comedies or farces, and a number of love-poems. Most of his works have been published, with a life, by Schedel (1844-1847).

CSOMA DE KOROS, ALEXANDER (c. 1790-1842), or, as the name is written in Hungarian, KOROSI CSOMA SANDOR, Hungarian traveller and philologist, born about 1790 at Koros in Transylvania, belonged to a noble family which had sunk into poverty. He was educated at Nagy-Enyed and at Gottingen; and, in order to carry out the dream of his youth and discover the origin of his countrymen, he divided his attention between medicine and the Oriental languages. In 1820, having received from a friend the promise of an annuity of 100 florins (about L10) to support him during his travels, he set out for the East. He visited Egypt, and made his way to Tibet, where he spent four years in a Buddhist monastery studying the language and the Buddhist literature. To his intense disappointment he soon discovered that he could not thus obtain any assistance in his great object; but, having visited Bengal, his knowledge of Tibetan obtained him employment in the library of the Asiatic Society there, which possessed more than 1000 volumes in that language; and he was afterwards supported by the government while he published a Tibetan-English dictionary and grammar (both of which appeared at Calcutta in 1834). He also contributed several articles on the Tibetan language and literature to the _Journal of the Asiatic Society of Bengal_, and he published an analysis of the _Kah-Gyur_, the most important of the Buddhist sacred books. Meanwhile his fame had reached his native country, and procured him a pension from the government, which, with characteristic devotion to learning, he devoted to the purchase of books for Indian libraries. He spent some time in Calcutta, studying Sanskrit and several other languages; but, early in 1842, he commenced his second attempt to discover the origin of the Hungarians, but he died at Darjiling on the 11th of April 1842. An oration was delivered in his honour before the Hungarian Academy by Eotvos, the novelist.

CTENOPHORA, in zoology, a class of jelly-fish which were briefly described by Professor T. H. Huxley in 1875 (see ACTINOZOA, _Ency. Brit._ 9th ed. vol. i.) as united with what we now term Anthozoa to form the group Actinozoa; but little was known of the intimate structure of those remarkable and beautiful forms till the appearance in 1880 of C. Chun's Monograph of the Ctenophora occurring in the Bay of Naples. They may be defined as Coelentera which exhibit both a radial and bilateral symmetry of organs; with a stomodaeum; with a mesenchyma which is partly gelatinous but partly cellular; with eight meridianal rows of vibratile paddles formed of long fused or matted cilia; lacking nematocysts (except in one genus). An example common on the British coasts is furnished by _Hormiphora_ (_Cydippe_). In outward form this is an egg-shaped ball of clear jelly, having a mouth at the pointed (oral) pole, and a sense-organ at the broader (aboral) pole. It possesses eight meridians (costae) of iridescent paddles in constant vibration, which run from near one pole towards the other; it has also two pendent feathery tentacles of considerable length, which can be retracted into pouches. The mouth leads into an ectodermal stomodaeum ("stomach"), and the latter into an endodermal funnel (infundibulum); these two are compressed in planes at right angles to one another, the sectional long axis of the stomodaeum lying in the so-called sagittal (stomodaeal or gastric) plane, that of the funnel in the transverse (tentacular or funnel) plane. From the funnel, canals are given off in three directions; (a) a pair of paragastric (stomachal, or stomodaeal) canals run orally, parallel to the stomodaeum, and end blindly near the mouth; (b) a pair of perradial canals run in the transverse plane towards the equator of the animal; each of these becomes divided into two short canals at the base of the tentacle sheath which they supply, but has previously given off a pair of short interradial canals, which again bifurcate into two adradial canals; all these branches lie in the equatorial plane of the animal, but the eight adradial canals then open into eight meridianal canals which run orally and aborally under the costae; (c) a pair of aboral vessels which run towards the sense-organ, each of which bifurcates; of the four vessels thus formed, two only open at the sides of the sense-organ, forming the so-called excretory apertures. These three sets of structures, with the funnel from which they rise, make up the endodermal coelenteron, or gastro-vascular system. The generative organs are endodermal by origin, borne at the sides of the meridianal canals as indicated by the signs [male] [female]. There exists a subepithelial plexus with nerve cells and fibres, similar to that of jelly-fishes. The sense-organ of the aboral pole is complex, and lies under a dome of fused cilia shaped like an inverted bell-jar; it consists of an otolith, formed of numerous calcareous spheroids, which is supported on four plates of fused cilia termed balancers, but is otherwise free. The ciliated ectoderm below the organ is markedly thickened, and perhaps functionally represents a nerve-ganglion: from it eight ciliated furrows radiate outwards, two passing under each balancer as through an archway, and diverge each to the head of a meridianal costa. These ciliated furrows stain deeply with osmic acid, and nervous impulses are certainly transmitted along them. Locomotion is effected by strokes of the paddles in an aboral direction, driving the animal mouth forwards through the water: each paddle or comb (Gr. [Greek: kteis]; hence Ctenophora) consists of a plate of fused or matted cilia set transversely to the costa. The myoepithelial cells (formerly termed neuro-muscular cells), characteristic of other Coelentera, are not to be found in this group. On the other hand there are well-marked muscle fibres in definite layers, derived from special mesoblastic cells in the embryo, which are embedded in a jelly; these in their origin and arrangement are quite comparable to the mesoderm of Triploblastica, and, although the muscle-cells of some jelly-fish exhibit a somewhat similar condition, nothing so highly specialized as the mesenchyme of Ctenophora occurs in any other Coelenterate. The nematocysts being nearly absent from their group, their chief function is carried out by adhesive lasso-cells.

A, Adradial canals.
F, Infundibulum.
I, Interradial canal.
M, Meridianal canal lying under a costa.
N, Ciliated furrow from sense pole to costa.
Pg, Paragastric canal.
SO, Sense-organ.
St, Stomodaeum.
Subs, Subsagittal costa.
Subt, Subtentacular costa.
T, Tentacle.
Ts, Boundaries of tentacle-sheath.]

T (centrally), Tentacular canal, and (distally) tentacle.
[male], Position of testes.
[female], Position of ovaries; other letters in fig. 1. The stomodaeum
lies in the sagittal plane, the funnel and tentacles in the
transverse or tentacular plane.]

The Ctenophora are classified as follows:--

Sub-class i. Tentaculata, Order 1. CYDIPPIDEA, _Hormiphora_.
" 2. LOBATA, _Deiopea_.
" 3. CESTOIDEA, _Cestus_.
" ii. Nuda, " _Beroe_.

The Tentaculata, as the name implies, may be recognized by the
presence of tentacles of some sort. The CYDIPPIDEA are generally
spherical or ovoid, with two long retrusible pinnate tentacles: the
meridianal and paragastric canals end blindly. An example of these has
already been briefly described. The LOBATA are of the same general
type as the first Order, except for the presence of four circumoral
auricles (processes of the subtransverse costae) and of a pair of
sagittal outgrowths or lobes, on to which the subsagittal costae are
continued. Small accessory tentacles lie in grooves, but there is no
tentacular pouch; the meridianal vessels anastomose in the lobes. In
the CESTOIDEA the body is compressed in the transverse plane,
elongated in the sagittal plane, so as to become riband-like: the
subtransverse costae are greatly reduced, the subsagittal costae
extend along the aboral edge of the riband. The subsagittal canals lie
immediately below their costae aborally, but continuations of the
subtransverse canals round down the middle of the riband, and at its
end unite, not only with the subsagittal but also with the paragastric
canals which run along the oral edge of the riband. The tentacular
bases and pouches are present, but there is no main tentacle as in
Cydippidea; fine accessory tentacles lie in four grooves along the
oral edge. The sub-class Nuda have no tentacles of any kind; they are
conical or ovoid, with a capacious stomodaeum like the cavity of a
thimble. There is a coelenteric network formed by anastomoses of the
meridianal and paragastric canals all over the body.

The embryology of _Callianira_ has been worked out by E. Mechnikov.
Segmentation is complete and unequal, producing macromeres and
micromeres marked by differences in the size and in yolk-contents.
The micromeres give rise to the ectoderm; each of the sixteen
macromeres, after budding off a small mesoblast cell, passes on as
endoderm. A gastrula is established by a mixed process of embole and
epibole. The mesoblast cells travel to the aboral pole of the embryo,
and there form a cross-shaped mass, the arms of which lie in the
sagittal and transverse planes (perradii).

Subs, Subsagittal costae.
Subt, Much reduced subtentacular costae.
Subt, Branch of the subtentacular canal which runs along the centre of
the riband.
Pg, Continuation of the paragastric canal at right angles to its
original direction along the lower edge of the riband. At the
right-hand end the last two are seen to unite with the subsagittal
canal.]

There can be but little question of the propriety of including Ctenophora among the Coelentera. The undivided coelenteron (gastro-vascular system) which constitutes the sole cavity of the body, the largely radial symmetry, the presence of endodermal generative organs on the coelenteric canals, the subepithelial nerve-plexus, the mesogloea-like matrix of the body--all these features indicate affinity to other Coelentera, but, as has been stated in the article under that title, the relation is by no means close. At what period the Ctenophora branched off from the line of descent, which culminated in the Hydromedusae and Scyphozoa of to-day, is not clear, but it is practically certain that they did so before the point of divergence of these two groups from one another. The peculiar sense-organ, the specialization of the cilia into paddles with the corresponding modifications of the coelenteron, the anatomy and position of the tentacles, and, above all, the character and mode of formation of the mesenchyme, separate them widely from other Coelentera.

The last-named character, however, combined with the discovery of two remarkable organisms, _Coeloplana_ and _Ctenoplana_, has suggested affinity to the flat-worms termed Turbellaria. _Ctenoplana_, the best known of these, has recently been redescribed by A. Willey (_Quart. Journ. Micr. Sci._ xxxix., 1896). It is flattened along the axis which unites sense-organ and mouth, so as to give it a dorsal (aboral) surface, and a ventral (oral) surface on which it frequently creeps. Its costae are very short, and retrusible; its two tentacles are pinnate and are also retrusible. Two crescentic rows of ciliated papillae lie in the transverse plane on each side of the sense-organ. The coelenteron exhibits six lobes, two of which Willey identifies with the stomodaeum of other Ctenophora; the other four give rise to a system of anastomosing canals such as are found in _Beroe_ and Polyclad Turbellaria. An aboral vessel embraces the sense-organ, but has no external opening. _Ctenoplana_ is obviously a Ctenophoran flattened and of a creeping habit. _Coeloplana_ is of similar form and habit, with two Ctenophoran tentacles: it has no costae, but is uniformly ciliated. These two forms at least indicate a possible stepping-stone from Ctenophora to Turbellaria, that is to say, from diploblastic to triploblastic Metazoa. By themselves they would present no very weighty argument for this line of descent from two-layered to three-layered forms, but the coincidences which occur in the development of Ctenophora and Turbellaria,--the methods of segmentation and gastrulation, of the separation of the mesoblast cells, and of mesenchyme formation,--together with the marked similarity of the adult mesenchyme in the two groups, have led many to accept this pedigree. In his Monograph on the Polyclad Turbellaria of the Bay of Naples, A. Lang regards a Turbellarian, so to say, as a Ctenophora, in which the sensory pole has rotated forwards in the sagittal plane through 90 deg. as regards the original oral-aboral axis, a rotation which actually occurs in the development of _Thysanozoon_ (Muller's larva); and he sees, in the eight lappets of the preoral ciliated ring of such a larva, the rudiments of the costal plates. According to his view, a simple early Turbellarian larva, such as that of _Stylochus_, most nearly represents for us to-day that ancestor from which Ctenophora and Turbellaria are alike derived. For details of this brilliant theory, the reader is referred to the original monograph.

LITERATURE.--G. C. Bourne, "The Ctenophora," in Ray Lankester's
_Treatise on Zoology_ (1900), where a bibliography is given; G.
Curreri, "Osservazioni sui ctenofori," _Boll. Soc. Zool. Ital._ (2),
i. pp. 190-193 et ii. pp. 58-76; A. Garbe, "Untersuchungen uber die
Entstehung der Geschlechtsorgane bei den Ctenophoren.," _Zeitschr.
Wiss. Zool._ lxix. pp. 472-491; K. C. Schneider, _Lehrbuch der
vergleich. Histologie_ (1902). (G. H. Fo.)

CTESIAS, of Cnidus in Caria, Greek physician and historian, flourished in the 5th century B.C. In early life he was physician to Artaxerxes Mnemon, whom he accompanied (401) on his expedition against his brother Cyrus the Younger. Ctesias was the author of treatises on rivers, and on the Persian revenues, of an account of India (which is of value as recording the beliefs of the Persians about India), and of a history of Assyria and Persia in 23 books, called _Persica_, written in opposition to Herodotus in the Ionic dialect, and professedly founded on the Persian royal archives. The first six books treated of the history of Assyria and Babylon to the foundation of the Persian empire; the remaining seventeen went down to the year 398. Of the two histories we possess abridgments by Photius, and fragments are preserved in Athenaeus, Plutarch and especially Diodorus Siculus, whose second book is mainly from Ctesias. As to the worth of the _Persica_ there has been much controversy, both in ancient and modern times. Being based upon Persian authorities, it was naturally looked upon with suspicion by the Greeks and censured as untrustworthy.

For an estimate of Ctesias as a historian see G. Rawlinson's
_Herodotus_, i. 71-74; also the edition of the fragments of the
_Persica_ by J. Giimore (1888, with introduction and notes and list of
authorities).

CTESIPHON, a large village on the left bank of the Tigris, opposite to Seleucia, of which it formed a suburb, about 25 m. below Bagdad. It is first mentioned in the year 220 by Polybius v. 45. 4. When the Parthian Arsacids had conquered the lands east of the Euphrates in 129 B.C., they established their winter residence in Ctesiphon. They dared not stay in Seleucia, as this city, the most populous town of western Asia, always maintained her Greek self-government and a strong feeling of independence, which made her incline to the west whenever a Roman army attacked the Parthians. The Arsacids also were afraid of destroying the wealth and commerce of Seleucia, if they entered it with their large retinue of barbarian officials and soldiers (Strabo xvi. 743, Plin. vi. 122, cf. Joseph. _Ant._ xviii. 9, 2). From this time Ctesiphon increased in size, and many splendid buildings rose; it had the outward appearance of a large town, although it was by its constitution only a village. From A.D. 36-43 Seleucia was in rebellion against the Parthians till at last it was forced by King Vardanes to yield. It is very probable that Vardanes now tried to put Ctesiphon in its place; therefore he is called founder of Ctesiphon by Ammianus Marcellinus (xxiii. 6. 23), where King Pacorus (78-110) is said to have increased its inhabitants and built its walls. Seleucia was destroyed by the Romans in A.D. 164. When Ardashir I. founded the Sassanian empire (226), and fixed his residence at Ctesiphon, he built up Seleucia again under the name of Veh-Ardashir. Later kings added other suburbs; Chosroes I. in 540 established the inhabitants of Antiochia in Syria, whom he had led into captivity, in a new city, "Chosrau-Antioch" (or "the Roman city") near his residence. Therefore the Arabs designate the whole complex of towns which lay together around Seleucia and Ctesiphon and formed the residence of the Sassanids by the name Madain, "the cities,"--their number is often given as seven. In the wars between the Roman and Persian empires, Ctesiphon was more than once besieged and plundered, thus by Odaenathus in 261, and by Canis in 283; Julian in 363 advanced to Ctesiphon, but was not able to take it (Ammianus xxiv. 7). After the battle of Kadisiya (Qadisiya) Ctesiphon and the neighbouring towns were taken and plundered by the Arabs in 637, who brought home an immense amount of booty (see CALIPHATE). From then, these towns decayed before the increasing prosperity of the new Arab capitals Basra and Bagdad. The site is marked only by the ruins of one gigantic building of brick-work, called Takhti Khesra, "throne of Khosrau" (i.e. Chosroes). It is a great vaulted hall ornamented with pilasters, the remainder of the palace and the most splendid example of Sassanian architecture (see ARCHITECTURE, vol. ii. p. 558, for further details and illustration). (Ed. M.)

CUBA (the aboriginal name), a republic, the largest and most populous of the West India Islands, included between the meridians of 74 deg. 7' and 84 deg. 57' W. longitude and (roughly) the parallels of 19 deg. 48' and 23 deg. 13' N. latitude. It divides the entrance to the Gulf of Mexico into two passages of nearly equal width,--the Strait of Florida, about 110 m. wide between Capes Hicacos in Cuba and Arenas in Florida (Key West being a little over 100 m. from Havana); and the Yucatan Channel, about 130 m. wide between Capes San Antonio and Catoche. On the N.E., E. and S.E., narrower channels separate it from the Bahamas, Haiti (50 m.) and Jamaica (85 m.). In 1908, by the opening of a railway along the Florida Keys, the time of passage by water between Cuba and the United States was reduced to a few hours.

The island is long and narrow, somewhat in the form of an irregular crescent, convex toward the N. It has a decided pitch to the S. Its length from Cape Maisi to Cape San Antonio along a medial line is about 730 m.; its breadth, which averages about 50 m., ranges from a maximum of 160 m. to a minimum of about 22 m. The total area is estimated at 41,634 sq. m. without the surrounding keys and the Isle of Pines (area about 1180 sq. m.), and including these is approximately 44,164. The geography of the island is still very imperfectly known, and all figures are approximate only. The coast line, including larger bays, but excluding reefs, islets, keys and all minute sinuosities, is about 2500 m. in length. The N. littoral is characterized by bluffs, which grow higher and higher toward the east, rising to 600 ft. at Cape Maisi. They are marked by distinct terraces. The southern coast near Cape Maisi is low and sandy. From Guantanamo to Santiago it rises in high escarpments, and W. of Santiago, where the Sierra Maestra runs close to the sea, there is a very high abrupt shore. To the W. of Manzanillo it sinks again, and throughout most of the remaining distance to Cape San Antonio is low, with a sandy or marshy littoral; at places sand hills fringe the shore; near Trinidad there are hills of considerable height; and the coast becomes high and rugged W. of Point Fisga, in the province of Pinar del Rio. On both the N. and the S. side of the island there are long chains of islets and reefs and coral keys (of which it is estimated there are 1300), which limit access to probably half of the coast, and on the N. render navigation difficult and dangerous. On the S. they are covered with mangroves. A large part of the southern littoral is subject to overflow, and much more of it is permanently marshy. The Zapata Swamp near Cienfuegos is 600 sq. m. in area; other large swamps are the Majaguillar, E. of Cardenas, and the Cienaga del Buey, S. of the Cauto river. The Isle of Pines in its northern part is hilly and wooded; in its southern part, very low, level and rather barren; a tidal swamp almost cuts the island in two. A remarkable feature of the Cuban coast is the number of excellent anchorages, roadsteads and harbours. On the N. shore, beginning at the W., Bahia Honda, Havana, Matanzas, Cardenas, Nuevitas and Nipe; and on the S. shore running westward Guantanamo, Santiago and Cienfuegos, are harbours of the first class, several of them among the best of the world. Mariel, Cabanas, Banes, Sagua la Grande and Baracoa on the N., and Manzanillo, Santa Cruz, Batabano and Trinidad on the S. are also excellent ports or anchorages. The peculiar pouch-shape of almost all the harbours named (Matanzas being a marked exception) greatly increases their security and defensibility. These pouch harbours are probably "drowned" drainage basins. The number of small bays that can be utilized for coast trade traffic is extraordinary.

In popular language the different portions of the island are distinguished as the Vuelta Abajo ("lower turn"), W. of Havana; the Vuelta Arriba ("upper turn"), E. of Havana to Cienfuegos--Vuelta Abajo and Vuelta Arriba are also used colloquially at any point in the island to mean "east" and "west"--Las Cinco Villas--i.e. Villa Clara, Trinidad, Remedios, Cienfuegos and Sancti Spiritus--between Cienfuegos and Sancti Spiritus; and Tierra Adentro, referring to the region between Cienfuegos and Bayamo. These names are extremely common. The province and city of Puerto Principe are officially known as Camaguey, their original Indian name, which has practically supplanted the Spanish name in local usage.

Five topographic divisions of the island are fairly marked. Santiago (now Oriente) province is high and mountainous. Camaguey is characterized by rolling, open plains, slightly broken, especially in the W., by low mountains. The E. part of Santa Clara province is decidedly rough and broken. The W. part, with the provinces of Matanzas and Havana, is flat and rolling, with occasional hills a few hundred feet high. Finally, Pinar del Rio is dominated by a prominent mountain range and by outlying piedmont hills and mesas. There are mountains in Cuba from one end of the island to the other, but they are not derived from any central mass and are not continuous. As just indicated there are three distinctively mountainous districts, various minor groups lying outside these. The three main systems are known in Cuba as the occidental, central and oriental. The first, the Organ mountains, in Pinar del Rio, rises in a sandy, marshy region near Cape San Antonio. The crest runs near the N. shore, leaving various flanking spurs and foothills, and a coastal plain which at its greatest breadth on the S. is some 20 m. wide. The plain on the N. is narrower and higher. The southern slope is smooth, and abounds in creeks and rivers. The portion of the southern plain between the bays of Cortes and Majana is the most famous portion of the Vuelta Abajo tobacco region. The mountain range is capriciously broken at points, especially near Bejucal. The highest part is the Pan de Guajaibon, near Bahia Honda, at the W. end of the chain; its altitude has been variously estimated from 2500 to 1950 ft. The central system has two wings, one approaching the N. coast, the other covering the island between Sancti Spiritus and Santa Clara. It comprehends a number of independent groups. The highest point, the Pico Potrerillo, is about 2900 ft. in altitude. The summits are generally well rounded, while the lower slopes are often steep. Frequent broad intervals of low upland or low level plain extend from sea to sea between and around the mountains. Near the coast runs a continuous belt of plantations, while grazing, tobacco and general farm lands cover the lower slopes of the hills, and virgin forests much of the uplands and mountains.

The oriental mountain region includes the province of Oriente and a portion of Camaguey. In extent, in altitude, in mass, in complexity and in geological interest, it is much the most important of the three systems. Almost all the mountains are very bold. They are imperfectly known. There are two main ranges, the Sierra Maestra, and a line of various groups along the N. shore. The former runs from Cape Santa Cruz eastward along the coast some 125 m. to beyond the river Baconao. The Sierra de Cobre, a part of the system in the vicinity of Santiago, has a general elevation of about 3000 ft. Monte Turquino, 7700-8320 ft. in altitude, is the highest peak of the island. Gran Piedra rises more than 5200 ft., the Ojo del Toro more than 3300, the Anvil de Baracoa is somewhat lower, and Pan de Matanzas is about 1267 ft. The western portions of the range rise abruptly from the ocean, forming a bold and beautiful coast. A multitude of ravines and gullies, filled with torrential streams or dry, according to the season of the year, and characterized by many beautiful cascades, seam the narrow coastal plain and the flanks of the mountains. The spurs of the central range are a highly intricate complex, covered with dense forests of superb woods. Many points are inaccessible, and the scenery is wild in the extreme. The mountains beyond Guantanamo are locally known by a variety of names, though topographically a continuation of the Sierra Maestra. The same is true of the chains that coalesce with these near Cape Maisi and diverge northwesterly along the N. coast of the island. The general character of this northern marginal system is much the same as that of the southern, save that the range is much less continuous. A dozen or more groups from Nipe in the E. to the coast N. of Camaguey in the W. are known only by individual names. The range near Baracoa is extremely wild and broken. The region between the lines of the two coastal systems is a much dissected plateau, imperfectly explored. The Cauto river, the only one flowing E. or W. and the largest of Cuba, flows through it westward to the southern coast near Manzanillo. The scenery in the oriental portion of the island is very beautiful, with wild mountains and tropical forests. In the central part there are extensive prairies. In the west there are swelling hills and gentle valleys, with the royal palm the dominating tree. The valley of the Yumuri, near Matanzas, a small circular basin crossed by a river that issues through a glen to the sea, is perhaps the most beautiful in Cuba.

A very peculiar feature of Cuba is the abundance of caverns in the limestone deposits that underlie much of the island's surface. The caves of Cotilla near Havana, of Bellamar near Matanzas, of Monte Libano near Guantanamo, and those of San Juan de los Remedios, are the best known, but there are scores of others. Many streams are "disappearing," part of their course being through underground tunnels. Thus the Rio San Antonio suddenly disappears near San Antonio de los Banos; the cascades of the Jatibonico del Norte disappear and reappear in a surprising manner; the Moa cascade (near Guantanamo) drops 300 ft. into a cavern and its waters later reissue from the earth; the Jojo river disappears in a great "sink" and later issues with violent current at the edge of the sea. The springs of fresh water that bubble up among the keys of the S. coast are also supposedly the outlets of underground streams.

The number of rivers is very great, but almost without exception their courses are normal to the coast, and they are so short as to be of but slight importance. The Cauto river in Oriente province is exceptional; it is 250 m. long, and navigable by small vessels for about 75 m. Inside the bar at its mouth (formed by a storm in 1616) ships of 200 tons can still ascend to Cauto. In Camaguey province the Jatibonico del Sur; in Oriente the Salado, a branch of the Cauto; in Santa Clara the Sagua la Grande (which is navigable for some 20 m. and has an important traffic), and the Damuji; in Matanzas, the Canimar; and in Pinar del Rio the Cuyaguateje, are important streams. The water-parting in the four central provinces is very indefinite. There are few river valleys that are noteworthy--those of the Yumuri, the Trinidad and the Guines. At Guantanamo and Trinidad are other valleys, and between Mariel and Havana is the fine valley of Ariguanabo. Of lakes, there are a few on the coast, and a very few in the mountains. The finest is Lake Ariguanabo, near Havana, 6 sq. m. in area. Of the almost innumerable river cascades, those of the Sierra Maestra Mountains, and in particular the Moa cascade, have already been mentioned. The Guama cascade in Oriente province and the Hanabanilla Fall near Cienfuegos (each more than 300 ft. high), the Rosario Fall in Pinar del Rio, and the Almendares cascade near Havana, may also be mentioned.

_Geology._--The foundation of the island is formed of metamorphic and
igneous rocks, which appear in the Sierra Maestra and are exposed in
other parts of the island wherever the comparatively thin covering of
later beds has been worn away. A more or less continuous band of
serpentine belonging to this series forms the principal watershed,
although it nowhere rises to any great height. It is in this band that
the greater part of the mineral wealth of Cuba is situated. These
ancient rocks have hitherto yielded no fossils and their age is
therefore uncertain, but they are probably pre-Cretaceous at least.
Fossiliferous Cretaceous limestones containing _Rudistes_ have been
found in several parts of the island (Santiago de los Banos, Santa
Clara province, &c.). At the base there is often an arkose, composed
largely of fragments of serpentine and granite derived from the
ancient floor. At Esperanza and other places in the Santa Clara
province, bituminous plant-bearing beds occur beneath the Tertiary
limestones, and at Baracoa a Radiolarian earth occupies a similar
position. The latter, like the similar deposits in other West Indian
islands, is probably of Oligocene age. It is the Tertiary limestones
which form the predominant feature in the geology of Cuba. Although
they do not exceed 1000 ft. in thickness, they probably at one time
covered the whole island except the summits of the Sierra Maestra,
where they have been observed, resting upon the older rocks, up to a
height of 2300 ft. They contain corals, but are not coral reefs. The
shells which have been found in them indicate that they belong for
the most part to the Oligocene period. They are frequently very much
disturbed and often strongly folded. Around the coast there is a
raised shelf of limestone which was undoubtedly a coral reef. But it
is of recent date and does not attain an elevation of more than 40 or
50 ft.

Minerals are fairly abundant in number, but few are present in
sufficient quantity to be industrially important. Traditions of gold
and silver, dating from the time of the Spanish conquest, still
endure, but these metals are in fact extremely rare. Oriente province
is distinctively the mineral province of the island. Large copper
deposits of peculiar richness occur here in the Sierra de Cobre, near
the city of Santiago; and both iron and manganese are abundant.
Besides the deposits in Oriente province, iron is known to exist in
considerable amount in Camaguey and Santa Clara, and copper in
Camaguey and Pinar del Rio provinces. The iron ores mined at Daiquiri
near Santiago are mainly rich hematites running above 60% of iron,
with very little sulphur or phosphorus admixture. The copper deposits
are mainly in well-marked fracture planes in serpentine; the ore is
pyrrhotite, with or without chalcopyrite. Manganese occurs especially
along the coast between Santiago and Manzanillo; the best ores run
above 50%. Chromium and a number of other rare minerals are known to
exist, but probably not in commercially available quantities.
Bituminous products of every grade, from clear translucent oils
resembling petroleum and refined naphtha, to lignite-like substances,
occur in all parts of the island. Much of the bituminous deposits is
on the dividing line between asphalt and coal. There is an endless
amount of stone, very little of which is hard enough to be good for
building material, the greatest part being a soft coralline limestone.
The best buildings in Havana are constructed of a very rich white
limestone, soft and readily worked when fresh, but hardening and
slightly darkening with age. There are extensive and valuable deposits
of beautiful marbles in the Isle of Pines, and lesser ones near
Santiago. The Organ Mountains contain a hard blue limestone; and
sandstones occur on the N. coast of Pinar del Rio province. Clays of
all qualities and colours abound. Mineral waters, though not yet
important in trade, are extremely abundant, and a score of places in
Cuba and the Isle of Pines are already known as health resorts. Those
near San Diego, Guanabacoa and Santa Maria del Rosario (near Havana)
and Madruga (near Guines) are the best known.

The soil of the island is almost wholly of modern formation, mainly
alluvial, with superficial limestones as another prominent feature. In
the original formation of the island volcanic disturbances and coral
growth played some part; but there are only very slight superficial
evidences in the island of former volcanic activity. Noteworthy
earthquakes are rare. They have been most common in Oriente province.
Those of 1776, 1842 and 1852 were particularly destructive, and of
earlier ones those of 1551 and 1624 at Bayamo and of 1578 and 1678 at
Santiago. Every year there are seismic disturbances, and though
Santiago is the point of most frequent visitation, they occur in all
parts of the island, in 1880 affecting the entire western end. Notable
seismic disturbances in Cuba have coincided with similar activity in
Central America so often as to make some connexion apparent.

_Flora._--The tropical heat and humidity of Cuba make possible a flora
of splendid richness. All the characteristic species of the West
Indies, the Central American and Mexican and southern Florida
seaboard, and nearly all the large trees of the Mexican tropic belt,
are embraced in it. As many as 3350 native flowering species were
catalogued in 1876. The total number of species of the island flora
was estimated in 1892 by a writer in the _Revista Cubana_ (vol. xv.
pp. 5-16) to be between 5000 and 6000, but hardly one-third of this
number had then been gathered into a herbarium, and all parts of the
island had not then been explored. It was estimated officially in 1904
that the wooded lands of the island comprised 3,628,434 acres, of
which one-third were in Oriente province, another third in Camaguey,
and hardly any in Havana province. Much of this area is of primeval
forest; somewhat more than a third of the total, belonging to the
government, was opened to sale (and speculative exspoliation) in 1904.
The woods are so dense over large districts as to be impenetrable,
except by cutting a path foot by foot through the close network of
vines and undergrowth. The jaguey (_Ficus_ sp.), which stifles in its
giant coils the greatest trees of the forest, and the copei (_Clusia
rosea_) are remarkable parasitic lianas. Of the palm there are more
than thirty species. The royal palm is the most characteristic tree of
Cuba. It attains a height of from 50 to 75 ft., and sometimes of more
than 100 ft. Alone, or in groups, or in long aisles, towering above
the plantations or its fellow trees of the forest, its beautiful crest
dominates every landscape. Every portion, from its roots to its
leaves, serves some useful purpose. From it the native draws lumber
for his hut, utensils for his kitchen, thatch for his roof, medicines,
preserved delicacies, and a long list of other articles. The corojo
palm (_Cocos crispa_) rivals the royal palm in beauty and utility;
oil, sugar, drink and wood are derived from it. The coco palm (_Cocos
nucifera_) is also put to varied uses. The mango is planted with the
royal palm along the avenues of the plantations. The beautiful ceiba
(_Bombax ceiba_ L., _Ceiba pentandra_) or silk cotton tree is the
giant of the Cuban forests; it often grows to a height of 100 to 150
ft. with enormous girth. The royal pinon (_Erythrina velatina_) is
remarkable for the magnificent purple flowers that cover it. The
tamarind and banyan are also noteworthy. Utilitarian trees and plants
are legion. There are at least forty choice cabinet and building
woods. Of these, ebonies, mahogany (for the bird's-eye variety such
enormous prices are paid as $1200 to $1800 per thousand board-feet),
culla (or cuya, _Bumelia retusa_), cocullo (cocuyo, _Bumelia nigra_),
ocuje (_Callophyllum viticifolia_, _Ornitrophis occidentalis_, _O.
cominia_), jigue (jique, _Lysiloma sabicu_), mahagua (_Hibiscus
tiliaceus_), granadillo (_Brya ebenus_), icaquillo (_Licania incania_)
and agua-baria (_Cordia gerascanthes_) are perhaps the most beautiful.
Other woods, beautiful and precious, include guayacan (Guaiacum
sanctum), baria (varia, _Cordia gerascanthoides_)--the fragrant,
hard-wood Spanish elm--the quiebra-hacha (_Copaifera hymenofolia_),
which three are of wonderful lasting qualities; the jiqui (_Malpighia
obovata_), acana (_Achras disecta_, _Bassia albescens_), caigaran (or
caguairan, _Hymenaea floribunda_), and the dagame (_Calicophyllum
candidissimum_), which four, like the culla, are all wonderfully
resistant to humidity; the caimatillo (_Chrysophyllum oliviforme_),
the yaya (or yayajabico, yayabito: _Erythalis fructicosa_, _Bocagea
virgata_, _Guateria virgata_, _Asimina Blaini_), a magnificent
construction wood; the maboa (_Cameraria latifolia_) and the jocuma
(jocum: _Sideroxylon mastichodendron_, _Bumelia saticifolia_), all of
individual beauties and qualities. Many species are rich in gums and
resins; the calambac, mastic, copal, cedar, &c. Many others are
oleaginous, among them, peanuts, sun-flowers, the bene seed (sesame),
corozo, almond and palmachristi. Others (in addition to some already
mentioned) are medicinal; as the palms, calabash, manchineel, pepper,
fustic and a long list of cathartics, caustics, emetics, astringents,
febrifuges, vermifuges, diuretics and tonics. Then, too, there are
various dyewoods; rosewood, logwood (or campeachy wood), indigo,
manaju (_Garcinia Morella_), Brazil-wood and saffron. Textile plants
are extremely common. The majagua tree grows as high as 40 ft.; from
its bark is made cordage of the finest quality, which is scarcely
affected by the atmosphere. Strong, fine, glossy fibres are yielded by
the exotic ramie (_Boehmeria nivea_), whose fibre, like that of the
majagua, is almost incorruptible; by the maya or rat-pineapple
(_Bromelia Pinguin_), and by the daquilla (or daiguiya--_Lagetta
lintearia_, _L. valenzuelana_), which like the maya yields a
brilliant, flexible product like silk; stronger cordage by the corojo
palms, and various henequen plants, native and exotic (especially
_Agave americana_, _A. Cubensis_); and various plantains, the exotic
_Sansevieria guineensis_, okra, jute, _Laportea_, various lianas, and
a great variety of reeds, supply varied textile materials of the best
quality. The yucca is a source of starch. For building and
miscellaneous purposes, in addition to the rare woods above named,
there are cedars (used in great quantities for cigar boxes); the pine,
found only in the W., where it gives its name to the Isle of Pines and
the province of Pinar del Rio; various palms; oaks of varying hardness
and colour, &c. The number of alimentary plants is extremely great.
Among economic plants should be mentioned the coffee, cacao, citron,
cinnamon, cocoanut and rubber tree. Wheat, Indian corn and many
vegetables, especially tuberous, are particularly important. Plantain
occurs in several varieties; it is in part a cheap and healthful
substitute for bread, which is also made from the bitter cassava,
after the poison is extracted. The sweet cassava yields tapioca.
Bread-trees are fairly common, but are little cared for. White and
sweet potatoes, yams, sweet and bitter yuccas, sago and okra, may also
be mentioned.