P18, Amer. Journ. of Science, Series II., vol. 24, p. 274, and in U.S. form and boundary of the region from which the light emanates, | Astron. Nachr., lxxiii. p. 199: Jacob, Memoirs RAS, xvi Professor A. W. Wright, of New Haven, also made careful cbservations leading to the conclusion that the spectrum differs from sunlight only in intensity. Some evidence has also been found by the same observer of polarization, showing that a considerable portion of the light must be reflected sunlight. The observations of Maxwell Hall also embraced some made with the spectroscope. He was unable to see any marked deviation of the spectrum from that of the sun; but it does not appear that either he or any other of the observers distinctly saw the dark lines of the solar spectrum. Direct proof that we have to do with reflected sunlight is therefore still incomplete. The question whether the Gegenschein can be accounted for by the reflection of light from the same matter as the zodiacal band is still unsettled. Taking the general consensus of the observations it would seem that its light must be so much brighter than that of the band as to imply the action of some different cause. In this connexion may be mentioned the ingenious suggestion of S. Arrhenius, that the phenomenon is due to corpuscles sent off by the earth and repelled by the sun in the same way that they are sent off from a comet and form its tail. In other words, the light may be an exceedingly tenuous cometary tail to the earth, visible only because seen through its very great length. The view that no cause intervenes additional to that producing the zodiacal band is strengthened, though not proved, by a theorem due to F. R. Moulton of Chicago. He shows that, supposing the cloud of particles to move around the sun in nearly circular orbits immediately outside the earth, the perturbations by the earth in the motion of the particles will result in their retardation in that part of the orbit nearest the earth, and therefore in their always being more numerous in a given space in this part of the orbit than in any other. This view certainly accounts for some intensification of the light, to which may be added the intensification produced by the vertical reflection of the sunlight. A new interest was given to the subject by the investigations of H. H. Seeliger, published in 1906, who showed that the observed excess of motion of the perihelion of Mercury may be accounted for by the action of that portion of the matter reflecting the zodiacal light which lies nearest to the sun. Plausible though his result is, the subject still requires investigation. It seems not unlikely that the final conclusion will be that instead of the reflecting matter being composed of solid particles it is an exceedingly tenuous gaseous envelope surrounding the sun and revolving on an axis the mean position of which is between that of the sun's equator and that of the invariable plane of the solar system. BIBLIOGRAPHY.-Childrey, Natural History of England (1659) and Britannia Baconica, p. 183 (1661); D. Cassini, Nouv. Phenom. d'une lumière céleste [zodiacale] (1683) and Découverte de la lumière céleste qui paroist dans le zodiaque (1685); R. Hooke, Explication of a Glade of Light, &c. (1685); Mairan, Observations de la lumière zodiacale; L. Euler, Sur la cause de la lumière zodiacale (1746); Mairan, Sur la cause de la lumière zodiacale (1747); R. Wolf, Beobachtungen des Zodiacaliichtes (1850-52): Brorsen Ueber den Gegenschein des Zodiacallichts (1855) and in Schumacher, 998; J. F. J. Schmidt, Das Zodiacallicht (Brunswick, 1856) and in ZOFFANY, JOHANN (1733-1810), British painter, whose in Frankfort-on-Main. He ran away from home at the age of father was architect to the prince of Thurn and Taxis, was born thirteen and went to Rome, where he studied art for nearly twelve years. In 1758 he left for England, and after undergoing some hardships was brought into fashion by royal patronage, and in 1769 was included among the foundaties members of the Royal Academy. He went to Florence in 1773 with an introduction from George III. to the grand duke of Tuscany, and did not return until 1779. During this second stay in Italy he met with much success, and was commanded by the empress Maria Theresa to paint a picture of the royal family of Tuscany; this work he executed so much to the satisfaction of the empress that in 1778 he was created a baron of the Austrian empire. He went next to India, where he lived from 1783 to 1790, to which period belong some of his bestknown paintings; but the last twenty years of his life were spent in England. He died in 1810 and was buried in Kew churchyard. His portrait groups of dramatic celebrities are, perhaps, the most highly esteemed of his many productions; they have considerable technical merit and show much shrewd insight into character. Several of the best are in the Garrick Club, London. ZOÏLUS (c. 400-320 B.C.), Greek grammarian of Amphipolis in Macedonia. According to Vitruvius (vii., preface) he lived during the age of Ptolemy Philadelphus (285-247 B.C.), by whom he was crucified as the punishment of his criticisms on the king. This account, however, should probably be rejected. Zellus appears to have been at one time a follower of Isocrates, but subsequently a pupil of Polycrates, whom he heard at Athens, where he was a teacher of rhetoric. Zoilus was chiefly known for the acerbity of his attacks on Homer (which gained him the name of Homeromastix, "scourge of Homer "), chiefly directed against the fabulous element in the Homeric poems. Zoilus also wrote against Isocrates and Plato, who had attacked the style of Lysias of which he approved. The name Zoilus came to be generally used of a spiteful and malignant critic. See U. Friedländer, De Zoilo aliisque Homeri Obtrectaterbas (Königsberg, 1895); J. E. Sandys, History of Classical Scholarship (2nd ed. 1906). ZOISITE, a rock-forming mineral, consisting of basic calcium and aluminium silicate, Ca2(AlOH)Al(SiO);, crystallizing in the orthorhombic system. It is closely related to epidote (6.1) both in the angles of the crystals and in chemical composition: a zoisite containing some iron replacing aluminium may be identical in composition with an epidote ("clinozoisite") poor in iron. The crystals are prismatic in habit and are deeply furrowed parallel to their length; terminal planes are rare. there is a perfect cleavage parallel to the brachy-pinacoid. Columnar and compact masses are more common. The hardness is 6 and the specific gravity 3-25-3-37. The colour is "thulite," occurs often grey; a rose-red variety, known as with sky-blue vesuvianite at Telemarken in Norway, and has been used to a limited extent as an ornamental stone. According to differences in the optical characters, two kinds of zoisite have been distinguished. Zoisite is a product of dynamometamorphism, and occurs as a constituent of some crystalline saus Zola played a very important part in the Dreyfus affair, which convulsed French politics and social life at the end of the 19th century. At an early stage he came to the conclusion that Dreyfus was the innocent victim of a nefarious conspiracy, and on the 13th of January 1898, with his usual intrepidity, he published in the Aurore newspaper, in the form of a letter beginning with the words J'accuse, a terrible denunciation of all those who had had a hand in hounding down that unfortunate officer. Zola's object was a prosecution for libel, and a judicial inquiry into the whole affaire, and at the trial, which took place in Paris in February, a fierce flood of light was thrown on the case. The chiefs of the army put forth all their power, and Zola was condemned. He appealed. On the 2nd of April the Cour de Cassation quashed the proceedings. A second trial took place at Versailles, on the 18th of July, and without waiting the result Zola, by the advice of his counsel and friends, and for reasons of legal strategy, abruptly left France and took refuge in England. Here he remained in hiding, writing Fécondité, till the 4th of June 1899, when, immediately on hearing that there was to be a revision of the first Dreyfus trial, he returned to Paris. Whatever may be thought of the affaire itself, there can be no question of Zola's superb courage and disinterested ness. schists, such as amphibolite and eclogite. It was first observed | touch. The first impression it produces may be one of heaviness, by Baron Zois (after whom it was named) in the eclogite of and the later "gospels " on population and work are distinctly Sau-Alpe in Carinthia; other localities are the Ducktown ponderous. But for rendering the gloomy horror of the subcopper mines in Tennessee, where it occurs embedded injects in which he most delights-detail on detail being accumuchalcopyrite; Loch Garve in Ross-shire, &c. The 66 lated till the result is overwhelming-Zola has no superior. surite" of the Alps and elsewhere, which has resulted from the Some of his descriptions of crowds in movement have never alteration of the plagioclase felspar of gabbro, consists largely been surpassed. of zoisite with epidote. (L. J. S.) ZOLA, ÉMILE ÉDOUARD CHARLES ANTOINE (1840-1902), French novelist, was born in Paris on the 2nd of April 1840, his father being an engineer, part Italian and part Greek, and his mother a Frenchwoman. The father seems to have been an energetic, visionary man, who, dying while his only son was a little lad, left to his family no better provision than a lawsuit against the municipality of the town of Aix It was at Aix, which figures as Plassans in so many of his novels, that the boy received the first part of his education. Thence he proceeded, in 1858, to Paris, where, as later at Marseilles, he failed to obtain his bachelor's degree. Then came a few years of terrible poverty; but at the beginning of 1862 he obtained a clerkship, at the modest salary of a pound a week, in the house of Hachette the publisher. Meanwhile he was writing apace, but nothing of particular merit. His first book, Contes à Ninon, appeared on the 24th of October 1864, and attracted some attention, and in January 1866 he determined to abandon clerking and take to literature. Vigorous and aggressive as a critic, his articles on literature and art in Villemessant's paper L'Événement created a good deal of interest. So did the gruesome but powerful novel, Thérèse Raquin (1867). Meanwhile, with characteristic energy, Zola was projecting something more important: the creation of a world of his own, like that of Balzac's Comédie Humaine-the history of a family in its various ramifications during the Second Empire. The history of this family, the Rougon-Macquart, was to be told in a series of novels containing a scientific study of heredity-science was always Zola's ignis fatuus-and a picture of French life and society. The first novel of the series, La Fortune des Rougon, appeared in book form at the end of 1871. It was followed by La Curée (1874), Le Ventre de Paris (1874), La Conquête de Plassans (1875), La Faute de l'Abbé Mouret (1875), Son Excellence Eugène Rougon (1876)-all books unquestionably of immense ability, and in a measure successful, but not great popular successes. Then came L'Assommoir (1878?), the epic of drink, and the author's fortune was made. Edition followed edition. He became the most discussed, the most read, the most bought novelist in France-the sale of L'Assommoir being even exceeded by that of Nana (1880) and La Débâcle (1892). From the Fortune des Rougon to the Docteur Pascal (1893) there are some twenty novels in the Rougon-Macquart series, the second half of which includes the powerful novels Germinal (1885) and La Terre (1888). In 1888 Zola departed from his usual vein in the idyllic story of Le Rêve. Zola also wrote a series of three romances on cities, Lourdes, Rome, Paris (1894-98), novels on the "gospels" of population (Fécondité) and work (Travail), a volume of plays, and several volumes of criticism, and other ZOLKIEWSKI, STANISLAUS (1547-1619), the most illustrious things. These books are based on study and observation; the member of an ancient Ruthenian family which emigrated to novels are crowded with characters. The whole is a gigantic Galicia in the 15th century. During the interregnum in Poland opus, the fruit of immense labour, of an admirable tenacity after the death of Henry of Valois, Zolkiewski was an ardent so many pages written, morning after morning, without inter-partisan of the chancellor Zamoyski, and supported the canmission, during some thirty years. He prided himself on his motto, Nulla dies sine linea. On the morning of the 29th of September 1902 Zola was found dead in the bedroom of his Paris house, having been accidentally asphyxiated by the fumes from a defective flue. He received a public funeral, at which Captain Dreyfus was present. Anatole France delivered an impassioned oration at the grave. At the time of his death Zola had just completed a novel, Vérité, dealing with the incidents of the Dreyfus trial. A sequel, Justice, had been planned, but not executed. After a life of constant struggle and an obloquy which never relaxed, the sensational close of Zola's career was the signal for an extraordinary burst of eulogy. The verdict of posterity will probably be kinder than the first, and less unmeasured than the second. Zola's literary position would have more than qualified him for the French Academy. He was several times a candidate in vain. (F. T. M.) See Emile Zola, Novelist and Reformer (1904), giving a full account of his life and work, by E. A. Vizetelly, who translated and edited many of his works in English; also P. Alexis, Emile Zola, Notes d'un ami; F Brunetière, Le Roman Naturaliste (1883); vols. iii., v and vi of the Journal des Goncourt (1888-92); E. Hennequin, Quelques Ecrivains français (1890), R. H. Sherard, Emile Zola a biographical and critical study (1903); A. Laporte, Emile Zola, l'homme et l'œuvre (1894) with a bibliography. A complete report of the proceedings against Zola is printed in Le Procès Zola (2 vols. 1898, Eng. trans. 1898). didature of Stephen Báthory, under whose banner he learned the art of war in the Muscovite campaigns. On the death of Zola was the apostle of the "realistic" or "naturalistic "Stephen, Zolkiewski vigorously supported the policy of Zamoyski, school; but he was in truth not a "naturalist" at all, in so and took an active part in the battle of Byczyna, when the far as naturalism" is to be regarded as a record of fact. He Austrian archduke Maximilian was defeated by the Polish was an idealist, but while other idealists idealize the nobler chancellor. Shortly afterwards Zolkiewski was made castellan elements in human nature, so has he, for the most part-the of Lemberg and acting commander-in-chief. On the accession later books, however, show improvement-idealized the elements of Sigismund III he retired from court and divided his time that are bestial. He saw man's lust, greed, gluttony, as in a between improving his estates, where he built towns and forvision, magnified, overwhelming, portentous. And what he tresses, and disciplining the Cossacks, with whom he enjoyed saw he presented with tremendous power. His style may lack great influence. In 1601-2 he served with distinction in the the classic qualities of French prose-lightness, delicacy, Livonian war against the Swedes, whom he defeated at Reval. sparkle; it certainly has not Daudet's colour and felicity of During the insurrection of Nicholas Zebrzydowski he led the ZOLLVEREIN (Ger. Zoll, toll, customs, and Verein, union), a term used generally for a certain form of Customs Union, but specially for the system among the German states which was in force between 1819 and 1871 (see TARIFF, and GERMANY: History). ZOMBOR, a town of Hungary, capital of the county of Bács Bodrog, 146 m. S. of Budapest by rail. Pop. (1900) 29.036, two-thirds Servians. It is situated in a fertile plain near the Franz Josef canal, which connects the Danube and the Thess, and is the centre of the corn and cattle trade of an extensive area. army which routed the rebels at Guzow in 1607, though pro- | die Natur der Cometen (Leipzig, 1872, 3rd ed. 1883). He died testing against the necessity of shedding "his brothers' blood." at Leipzig on the 25th of April 1882. For his services he received the palatinate of Kiev. He was opposed to the expedition sent to place the false Demetrius on the throne of Muscovy; but nevertheless accompanied the king to Smolensk and was sent thence with a handful of men against Moscow. On his way thither he defeated and captured Tsar Vasily Shuiski at the battle of Klushino (July 14, 1610), and two months later entered the Russian capital in triumph. His tactful and conciliatory diplomacy speedily won over the boyars, whom he persuaded to offer the Muscovite crown to the Polish crown prince, Wladislaus. For a moment it seemed possible that the Vasa family might occupy the throne of Ivan the Terrible; but Sigismund III. would not consent to the re- ZONARAS, JOANNES (JOHN), Byzantine chronicler and theoception of his son into the Greek Church, and refused to ratify logian, flourished at Constantinople in the 12th century. Under the terms made with the boyars. Zolkiewski then returned | Alexius I. Comnenus he held the offices of commander of the to the Polish camp and assisted in the reduction of Smolensk, bodyguard and private secretary to the emperor, but in the but Moscow in the meantime drove out the Polish garrison and succeeding reign he retired to Hagia Glykeria (one of the Princes' proclaimed a native dynasty under Michael Romanov. When Islands), where he spent the rest of his life in writing books. Zolkiewski presented his captives, Tsar Vasily and his family, His most important work, 'Eniroμn Ioropa (compendium to the Polish diet, he received an ovation and was rewarded with of history), in eighteen books, extends from the creation of the the dignity of hetman wielki (commander-in-chief). For the world to the death of Alexius (1118). The earlier part is largely next few years he defended the Ukraine against the Tatars drawn from Josephus; for Roman history he chiefly followed and Cossacks, and in 1617 was involved in a war with the Porte Dio Cassius, whose first twenty books are not otherwise known to owing to the unauthorized interference of the Polish nobles us. His history was continued by Nicetas Acominatus. Various in the affairs of Wallachia and Moldavia. Unable to defeat ecclesiastical works have been attributed to Zonaras-comthe vastly superior forces of the Turkish commander Skinder, mentaries on the Fathers and the poems of Gregory of Nazianzus, he concluded with him an advantageous truce at Jaruda (27th lives of Saints; and a treatise on the Apostolical Canorsof August 1618), by the terms of which he pledged himself to and there is no reason to doubt their genuineness. The lexicon, curb the Cossacks and at the same time renounced all the claims however, which has been handed down under his name (ed. of Poland to the Danubian principalities. Thus he saved the J. A. H. Tittmann 1808) is probably the work of a certain one army of Poland to guard her southern frontier from appa- Antonius Monachus (Stein's Herodotus, ii. 479 f.). rently inevitable destruction. On his return he was fiercely assailed by the diet for not risking everything in a pitched battle, but Zolkiewski defended himself with an eloquence which silenced his most venomous opponents. The peace of Jaruda was then confirmed, and the king conferred upon Zolkiewski the grand-chancellorship, an honour he had neither desired nor expected. Fresh attacks were presently made against him for failing, it was alleged, to prevent the Tatar incursions. So deeply wounded was the hero by these calumnies that when in 1619 he was sent against the Turks he publicly declared that he would never return alive unless victorious. He was as good as his word. Surrounded near the Dniester by countless hosts of Turks, Tatars and Janissaries, he retreated through the Steppes, fighting night and day without food or water, towards Cecora. By the time he reached it, he saw clearly that success was impossible, and deliberately determined to die where he stood. Disguising himself so that his dead body might not be recognized, he turned upon the pursuers and was slain after a desperate resistance (6th of October 1620). His head was cut off, exhibited in the Turkish camp and then sent to Constantinople as a present to the sultan, from whom it was subsequently ransomed at a great price. Zolkiewski is one of the most heroic figures in Polish history. An accomplished general, a skilful diplomatist, and a patriot who not only loved his country above all things, but never feared to tell his countrymen the truth, he excelled in all private and public virtues. As a writer he made a name by an important history of his Muscovite campaigns. See Stanislaw Gabryel Kozlowski, Life of Stanislaus Zolkiewski (Pol.) (Cracow, 1904). (R. N. B.) ZÖLLNER, JOHANN KARL FRIEDRICH (1834-1882), German astronomer and physicist, was born at Berlin on the 8th of November 1834. From 1872 he held the chair of astrophysics at Leipzig University. He wrote numerous papers on photometry and spectrum analysis in Poggendorff's Annalen and Berichte der k. sächsischen Gesellschaft der Wissenschaften, two works on celestial photometry (Grundzüge einer allgemeinen Photometric des Himmels, Berlin, 1861, 4to, and Photometrische Untersuchungen, Leipzig, 1865, 8vo), and a curious book, Ueber Complete edition in Migne, Patrologia Gracca, cxxxiv. cruv. cxxxvii.; the Chronicon by M. Pinder and T. Büttner-Wobst in the Bonn Corpus Scriptorum Hist. Byz. (1841-97) and by L. Dadorf in the Teubner series (1868-76); see bibliography in C. Krusbacher, Geschichte der byzantinischen Litteratur (2nd ed. 1897). ZONE (Gr. Javn, a girdle, from twvvival, to gird), a term for a belt or girdle, now used chiefly in the transferred sense of a demarcated area. Thus the earth's surface is divided, for classification of climates, into five climatic zones: the two temperate and the two frigid zones and the tropical or torrid zone. (See CLIMATE AND CLIMATOLOGY.) ZOOLOGICAL DISTRIBUTION (also known as Zoogeography), the science dealing, in the first place, with the distribution of living animals on the surface of the globe (both land and water), and secondly with that of their forerunners (both in time and in space). The science is thus a side-branch of zoology, intimately connected on the one hand with geography and on the other with geology. It is a comparatively modern science, which dates, at all events in its present form, from the second half of the 19th century. The Different parts of the land-surface of the globe are inhabited by different kinds of animals, or, in other words, by different faunas. These differences, in many cases at any rate, are not due to differences of temperature or of climate; and they do not depend on the distance of one place from another. warm-blooded land-animals of Japan are, for example, very much more closely related to those of the British Isles tha is the corresponding fauna of Africa to that of Madagascar. Again, on the hypothesis of the evolution of one species from another, in the case of land-animals unprovided with the mears of flight such resemblances and differences between the faunas of different parts of the world depend in a great degree on the presence or absence of facilities for free communication by land between the areas in question. Prima facie, therefore, it is natural to suppose that the fauna of an island will difer more from that of the adjacent continent than will those of different parts of that continent from one another. To a great extent this is the case; and if the present continents and islands had always been in statu quo, the proposition 1 For the distribution of plants, see PLANTS: Distribution. would, for the most part at any rate, be universally true. Geology has, however, taught us that many parts of what are now continents formed at earlier periods of the earth's history portions of the ocean-bed, while what are now islands have in some instances been connected with the adjacent mainlands, or even with land-masses the sites of which are now occupied by the open sea. We can hope, therefore, to understand and explain the present distribution of terrestrial animal life only by taking into account what geology teaches us as to past changes in the configuration of the land-masses of the globe, accompanied by investigations into the past history of animals themselves, as revealed by their fossil remains. Although to understand the reason of many facts in the present distribution of animals-as, for example, why tapirs are confined to the Malay countries and South America-it is essential to study fossil faunas, yet it has been found possible from the consideration of existing faunas alone to map out the landsurface of the globe into a number of zoological "regions," or provinces, more or less independent of the ordinary geographical boundaries, and severally characterized by a greater or smaller degree of distinctness in the matter of their faunas. One of the pioneers in this line of research was Dr P. L. Sclater, who in a paper on the geographical distribution of birds, published in the Journal of the Linnean Society of London for 1858, was enabled to define and name six of such zoological regions; these being mamly based on the distribution of the perching or passerine birds. Two years later Dr A. Russel Wallace, in the same journal, discussed in some detail the problems presented by the distribution of animals in the Malay Archipelago and Australasia. This preliminary essay was followed in 1876 by the appearance of the latter author's Geographical Distribution of Animals, an epoch-making work, which may be said to have first put the study of the distribution of animals generally on a thoroughly firm and scientific basis. With some slight modifications, the names proposed for the six zoological regions by Dr Sclater were adopted by Dr Wallace. Certain changes in regard to the limits and number of the zoological regions adopted by Sclater and Wallace have been proposed; but the original scheme forms the basis of all the later modifications, and these eminent naturalists are entitled to be regarded as the fathers of the study of distributional zoology. T. H. Huxley was also one of those who did much to advance the science in its carly days, while among those who have proposed more or less important modifications of the original scheme special mention may be made of Dr W. T. Blanford, Dr A. Heilprin, Prof. P. Matschie and Prof. Max Weber. The zoological regions proposed by Dr Sclater were based mainly on the distribution of the perching birds; but in the writings of Dr Wallace and of later authors mammals were very largely taken into consideration, and in later schemes there has been a similarly extensive use of the evidence afforded by mammalian distribution. That different groups of animals do not agree with another in the matter of geographical distribution will be evident when we reflect that in many instances there are very great differences in the relative ages of such groups, or, at all events, in the dates of their dispersal, or "radiation," over the surface of the earth. The radiation and dominance of reptiles, for example, greatly antedated that of either birds or mammals. Consequently, the zoological regions indicated by the present geographical distribution of the former group are very different from those suggested by the distribution of the two latter. If zoological regions are based on the evidence of the existing distribution of animals, groups with a relatively late radiation are clearly to be preferred to those the dispersal of which was earlier Mammals and birds, therefore, are of greater value from this point of view than reptiles; while the absence of the power of flight in the great bulk of the class renders the evidence afforded by mammals superior to that derived from birds. The marked general agreement between the geographical distribution of birds on the one hand and of mammals on the other is, however, a fact of the greatest importance in regard to the value of the zoological regions established on their evidence. Further testimony in the same direction is afforded by the distribution of certain other groups, more especially spiders (Arachnida); and it is also noteworthy that the distribution of the three main divisions of the human race accords to a certain extent with the boundaries of some of the zoological regions based on the distribution of the lower animals. With regard to the theory of the polar origin of life and the gradual dispersal of animals from the arctic regions, it may be briefly stated that the presumed series of radiations of life southward from the northern pole can have nothing to do with the present geographical distribution of animals, since we have abundant evidence that mammals have been spread over the whole of the warmer parts of the globe since, at any rate, the commencement of the Tertiary period, while the radiation of reptiles commenced at a much earlier epoch. As regards barriers to the free dispersal of nonvolant terrestrial animals these may be grouped under two main heads, namely, climatic and geographical, of which the second is by far the more important. At the present day a certain number of animals are fitted to live respectively only in hot and in cold climates. The man-like apes and elephants among mammals, and trogons and parrots among birds, are, for example, now exclusively dwellers in tropical or subtropical climates; whereas the polar bear, the musk-ox and ptarmigan are equally characteristic of the arctic zone. To a great extent this must be regarded as a comparatively modern adaptive feature, since many of these arctic and tropical animals belong to groups the distribution of which, either in the past or the present, is more or less independent of climate. Elephants, for instance, formerly inhabited Siberia at a time when the climate, although probably less cold than at present, was certainly not tropical; while the polar bear is a specialized member of a group some of the representatives of which are denizens of the tropics. It is true, indeed, that within the limits of the different zoological regions temperature-control has had an important influence on the distribution of animals, and has resulted in certain cases in the formation of life-zones, as in North America. As remarked, however, by H. A. Pilsbry and J. H. Ferriss1 in connexion with the distribution of land-molluscs," the lifezones of the United States as mapped by Dr C. H. Merriam emphasize the secondary and not the primary facts of distribution. The laws of temperature-control do not define transcontinental zones of primary import zoologically. These zones are secondary divisions of vertical life-areas of which the molluscan faunas were evolved in large part independently." And what is true of molluscs will hold good in the case of several other groups. Proc. Academy of Philadelphia, 1906, p. 123. There is also the phenomenon of vertical temperature-control. | animals from the north towards the south, that there is decisive On this subject Dr A. R. Wallace has written (Ency. Brit., evidence to prove the existence during the Tertiary period (so 9th ed., art." Distribution "): "As we ascend lofty mountains, far at least as mammals are concerned) of certain great centres the forms of life change in a manner somewhat analogous to of development, and in some instances, at all events, also of the changes observed in passing from a warm to a cold country. radiation, in the southern hemisphere; one of these developThis change is, however, far less observable in animals than in mental centres being in Africa a second in South America, and plants; and it is so unequal in its action, and can so frequently a third in Australia. be traced to mere change of climate and deficiency of food, that it must rank as a phenomenon of secondary importance. Vertical distribution among animals will be found in most cases to affect species rather than generic or family groups, and to involve in each case a mass of local details. The same remarks apply to the bathymetrical zones of marine life. Many groups are confined to tidal, or shallow, or deeper waters; but these differences of habit are hardly geographical, but involve details, suited rather to the special study of individual groups." Temperature-control is therefore mainly a factor which has acted independently in the different zoological regions of the globe, and as such demands little or no further mention in a general sketch of the present nature. The same remark will apply in the case of the influence of humidity on distribution, and also as regards "station." To illustrate the latter we may take the instances of the European squirrel and the chamois, the former of which is found only in wooded districts and is entirely absent from the open plains, while the latter occurs only in the isolated mountain ranges of the Pyrenees, the Alps, the Apennines and the Caucasus. The distributional area of both may, however, be regarded as including Europe generally, so that these local restrictions of range have nothing to do with the wider problems of distribution. Very different is the case with regard to geographical barriers to the free dispersal of terrestrial animals. It should be observed, however, that even these act with different degrees of intensity in the case of different groups. From the fact that the great majority of them are oviparous, reptiles, whose powers of dispersal in the adult state are generally as restricted as those of mammals, have an advantage over the latter in that their eggs may be carried long distances on floating timber down rivers and thence across the ocean, or may even be occasionally transported by birds. The eggs of batrachians, like those of fresh-water fishes, will in some cases at any rate withstand being frozen, and hence conceivably may be transported by floating ice. Adult insects may be carried in the same manner as the eggs of reptiles. After all, however, such unusual means of transport are probably of no great importance; and it seems most likely that the varying features in the geographical distribution of different groups of animals are due much more to differences in the dates of radiation, or dispersal of those groups, than to varying degrees of facility for overcoming natural geographical barriers to dispersal. The greatest barriers of all are formed by the ocean and the larger rivers; and from the former factor it follows that zoological regions coincide to a considerable extent-although by no means altogether-with the main geographical (as distinct from political) divisions of the earth's surface. In the main, mammals and other nonvolant terrestrial animals are debarred from crossing anything more than comparatively narrow channels of the sea, while even these and the larger rivers form a more or less effectual barrier to the dispersal of the great majority of the species. Hence it results that oceanic islands are usually devoid of such forms of life; while it may be laid down, as a general rule, that the existence of nearly allied types of terrestrial animals in countries now separated by stretches of sea implies a former land-connexion between them. There are, however, in many cases great difficulties in determining the nature of such connexions, largely owing to the fact that we are still in the dark as to whether the dispersal of many groups of animals has taken place down the lines of the present continents from north to south or equatorially by means of belts of land long since swallowed up by the ocean. In this connexion it may be remarked, as tending against the old idea of the radiation of all the modern groups of terrestrial To the general law that straits and arms of the sea form an effectual barrier to the dispersal of the larger land-animals, and more especially mammals, certain exceptions may be pleaded. Jaguars have, for instance, been known to cross the Rio de la Plata, while tigers constantly swim from island to island in the delta of the Ganges and probably also in the Malay Archipelago, and a polar bear has been observed swimming twenty miles away from land in Bering Sea. Deer, certain antelopes, pigs and elephants are also good swimmers; while hippopotamuses and crocodiles-especially the latter-ca3 cross channels of considerable width. The great tropical and subtropical rivers also carry down masses of floating soil er large trees upon which mammals and reptiles are borne, and although in many or most instances such are swept out to sea and their occupants drowned, in other instances they may be stranded upon the opposite bank or shore where their living freight can effect a landing. Such instances, however, cannot be very frequent, and they cannot affect widely sundered countries, owing to the lack of food supplies. Moreover, supposing a mammal to have reached a new land, unless it happened to be a pregnant female, or unless ancther individual of the opposite sex be similarly stranded, it would eventually die without progeny. Even in the case of a pregnant female, there is no certainty that the offspring, if but one, would be a male; and even supposing this to be the case, the progeny might perish from the attacks of other animals or from inbreeding. On the whole, it may be said, that instances of such methods of dispersal must be relatively few and can affect only countries not very widely sundered. The most important case that can be cited is the occurrence of a pig and an extinct hippopotamus in Madagascar, which probably reached that island by swimming from Africa. As a rule, a strait like that separating Ceylon from India may be considered an effectual barrier to the dispersal of large land-animals. Although the Rio de la Plata has effectually prevented the amphibious carpincho from reaching Argentina, deserts form even more impassable barriers than large rivers, the Sahara having prevented the North African fauna from reaching the heart of that continent. High and continuous mountainranges are likewise most effective in restricting the range ci animals; this being more especially the case when, like the Himalaya, their trend is equatorial instead of, as in the case of the Rocky Mountains and the Andes, from north to south la the direction of the main continental extension. Forests also present great obstacles to animal migration, although this is to a great extent of a local nature and comes, in fact, under the category of "station." Indeed, there appears to be no instance of the separation of one zoological region from another by forest alone. Lastly it should be mentioned that ice may serve as a factor in the dispersal of animals by acting as a bridge between different land-areas; and at some period this means of communcation may have aided in the great migrations of animals that have taken place between the Old and the New World by way of what is now Bering Sea. I. TERRESTRIAL DISTRIBUTION The zoological regions recognized by Dr A. R. Wallace in 1876, which are in the main identical with those Zoological proposed by Dr P. L. Sclater in 1858, and are chiefly Regions. based on the distribution of birds and mammals, are as follows: temperate Asia from the high Himalaya and west of the Indes 1. Palaearctic, which includes Europe to the Azores and Iceland, with Japan, and China from Ningpo and to the north of the watershed |