We may a.s.sume that every animal gradually extends its range by migration, as the result of the natural increase of the species necessitating a search for fresh feeding grounds. Every species thus tends to slowly take possession of all the habitable parts of the globe to which it has access. They would all naturally spread from their original homes in every direction, unless prevented by an impa.s.sable barrier. We have already learned that to all land animals, the sea acts as such a barrier. Mountains and rivers act also in a similar way, but not to the same extent. It is not difficult to understand also that a forest may be a formidable barrier to a typical inhabitant of the open country and _vice versa_, whilst a desert is impa.s.sable to almost all terrestrial organisms. Some species are scarcely affected by climate, and flourish equally well in the tropics and in temperate or cold countries; the majority, however, are greatly influenced by it. "No more striking ill.u.s.tration," remarks Merriam (p. 38), "could be desired of the potency of climate compared with the inefficiency of physical barriers, than is presented by the almost total dissimilarity of the North American Tropical and Sonoran Regions, though in direct contact, contrasted with the great similarity of the Boreal Regions of North America and Eurasia, now separated by broad oceans, though formerly united, doubtless, in the region of Behring Sea."

To return to the composition of the European fauna, we now know positively that a number of the mammals and birds inhabiting Central and Eastern Europe are of Siberian origin. How they came, and when, will form the subject for discussion in Chapter V. At present it will suffice to mention that in the superficial deposits belonging to the Pleistocene series of the North European plain have been discovered the remains of many typical members of the Siberian Steppe-fauna. Some of these, such as the Saiga-Antelope (_Saiga tartarica_), Fig. 2, still inhabit portions of Eastern Europe, whilst others have retreated to their native land. But it might be asked, how is it known that these species did not originate in Europe, and thence migrate to Siberia? Because if they had originated on our continent, they would have spread there. They would have invaded Northern and Southern Europe, and they would probably have left some remains in Spain, Italy, or Greece. They would also have left some of their relations in Europe; but all their nearest allies, too, are Asiatic. Moreover,--and this completes, I think, the proof of their Siberian origin,--the Pleistocene remains of these animals in Europe become less abundant, and the number of species likewise decreases, as we proceed from east to west. With these remains of Steppe animals are generally a.s.sociated those of others, which we must also look upon as Siberian emigrants, such as the Pikas or tailless Hares belonging to the genus _Lagomys_, the pouched Marmots (_Spermophilus_), and others. Some of them, as I have mentioned, still inhabit Central and Eastern Europe, whilst others have a wider distribution on our continent.

[Ill.u.s.tration: Fig. 2.--The Saiga-Antelope (_Saiga tartarica_). (From Lydekker's _Royal Natural History_, vol. ii. p. 298.)]

This migration must have been an unusually large one. It has been suggested that the Glacial period had some connection with it, and there can be little doubt, as we shall see later on, that a change of climate probably brought about this great Siberian invasion of Europe. But other causes might tend in the same direction, such as want of sufficient food after a few years of great increase of any particular species. It is not known to what we owe the periodic visits of the Central Asiatic Sandgrouse (_Syrrhaptes paradoxus_), Fig. 3, but certain it is that immense flocks of these birds invade Europe from time to time at the present day, just as those mammals may have done in past ages.

[Ill.u.s.tration: Fig. 3.--Central Asiatic Sandgrouse (_Syrrhaptes paradoxus_).]

The _Siberian_ migrations will be spoken of in the subsequent pages, as the Siberian element of the European fauna. These migrations, however, are not the only ones which reached Europe from Asia. The sixth chapter deals with migrations which have influenced our fauna far more than the Siberian. The latter did not last long, nor did they affect the whole of Europe. But what I may call the _Oriental_ migrations spread to every corner of Europe and certainly lasted throughout the whole of the Tertiary Era. The Oriental element came probably from Central and Southern Asia, and in its march to Northern Europe it was joined by local European migrations. For on our continent, too, animals originated and spread in all directions from their centres of dispersal. A separate chapter has been given to the _Alpine_ fauna, and another to that of South-western Europe, which will be known by the name of the _Lusitanian_ element. Finally, animals have also reached us from the north, and in the fourth chapter the history of that remarkable migration will be fully discussed under the t.i.tle of the _Arctic_ element of the European fauna.

It is generally believed that Africa played an important role in the peopling of our continent, but this is quite a mistake. The eminent Swiss palaeontologist Rutimeyer was quite right in saying (p. 42) that it is much more probable that Morocco, Algeria, and Tunis were stocked with animals by way of Gibraltar, and perhaps also by Sicily and Malta, from Europe, than the South of Europe from Africa.

I have already referred to what are known as "centres of dispersion" of animals, but before continuing to explain the general outline of this book, it will be necessary to make a few additional remarks on the subject.

Since every animal naturally tends to spread in every direction from its original home--that is to say, from the place of its origin--the latter should correspond with the centre of its range. And in any particular group of animals the maximum number of species should be formed in the area or zone which is the centre of its distribution. In the great majority of instances this is probably the case, in the higher animals perhaps less so than in the lower; still the rule must hold good that the original home of a species is generally indicated by the centre of its geographical distribution.

Take for example our familiar Badger (_Meles taxus_). It inhabits Europe and Northern Asia. It is absent apparently from many parts of Central Asia, but it appears again farther south in Palestine, Syria, Persia, Turkestan, and Tibet. West Central Asia would be about the centre of its range. That this corresponds to its place of origin is indicated by the fact that the only three other Badgers known--viz., _M.

anak.u.ma_, _M. leucurus_, and _M. albogularis_--are confined to Asia. If we examine the fossil history of the genus, we find that the two most ancient instances of the existence of Badgers have been discovered in Persia, where _M. Polaki_ and _M. maragha.n.u.s_ occur in miocene deposits.

The latter had migrated as far west as Greece in miocene times; no other trace of the Badger, however, is known from Europe until we come to the pleistocene beds. There are a good many cases known among mammals where the centre of dispersion would indicate to us a similar origin. On the other hand, there may be no fossil evidence of the occurrence of a species, or of its ancestors, in Asia, whilst such has been discovered in Europe. I think, however, that the present range of a species forms a safer criterion for the determination of its original home, as the Asiatic continent is still practically unworked from a palaeontological point of view. In a letter which I received from Professor Charles Deperet, he advocates the view that the wild Boar (_Sus scrofa_) is probably of European, and not, as I maintained (_c_, p. 455), of Asiatic origin; because there seemed to be a direct descent from Hyotherium of the middle miocene of Europe, through the upper miocene Pig of the Mount Leberon (_Sus major_) and of Eppelsheim (_Sus antiquus_), and the pliocene Pigs of Montpellier (_Sus provincialis_) and of the Auvergne (_Sus arvernensis_). No doubt this appears rather a strong case in favour of the European origin of the wild Boar, but although the Tertiary strata of Asia, as I remarked, are as yet little known, a number of fossil pigs are known from India, Persia, and China, the oldest being the upper miocene Persian Pig (_Sus maragha.n.u.s_). Pigs are therefore as old in Asia as in Europe, and as a direct intercourse between the two continents probably never ceased since miocene times, it is not surprising that this genus should occur in both. Even if the genus had its origin in Europe, it is quite possible that in later Tertiary times, the active centre of origin was shifted to the neighbouring continent, and that henceforth many new species issued forth from Asia, some of which may subsequently have been modified on reaching our continent. The wild Boar (_Sus scrofa_), however, to judge from its general range, I must look upon as merely an immigrant in Europe. I have no doubt that it originated somewhere in Asia, probably in the south.

The view I take of the origin of our European Boar is also supported by Dr. Forsyth Major's recent researches. He was led to a re-investigation of the history of the Pig while examining a large number of fossil skulls in the Museum at Florence, and came to the conclusion that only three or four species of recent wild pigs can be clearly distinguished (_b_, p. 298). One of these, viz., _Sus vittatus_, he thinks, is traceable in slight modifications from Sardinia to New Guinea and from j.a.pan to South Africa. The centre of distribution of this species lies in Southern Asia. Of the three remaining species, two, viz., _Sus verrucosus_ and _S. barbarus_, are entirely confined to the great islands which form part of the Malay Archipelago. Finally, _Sus scrofa_, our Central European wild Boar, is so closely related to _S. vittatus_ that the Sardinian Boar might be looked upon as a variety of either the one or the other. At any rate, Dr. Major recognises clearly in _Sus vittatus_ the representative of the ancestral stock of which _Sus scrofa_ is a somewhat modified offshoot.

The fauna of Europe consists, as I have mentioned, to a large extent of immigrants from the neighbouring continents. This is especially noticeable among the higher animals. When we come to the lower, such as the amphibia, we find a larger percentage, and among the land mollusca the great majority, to be of European origin. The foreigners are, as we learned, called Orientals, Siberians, and Arctics. For the sake of convenience, only two of the great European centres of origin have a chapter devoted to themselves, namely, the Alpine and the Lusitanian centres. There is another, however, of almost equal importance which lies in the east.

In the British Islands there is only an exceedingly small and insignificant group of species which are peculiar, and which we may consider to have had their origin there. Almost the whole of the British fauna is composed of streams of migrants which came from the north, south, and east, though many of these immigrant species have since their arrival been more or less distinctly modified into varieties or local races.

The eminent French conchologist Bourguignat (_a_, p. 352) was of opinion that, as far as terrestrial mollusca were concerned, there are in Europe three princ.i.p.al centres of creation or dispersion--all situated in mountainous countries and not in the plains. He distinguished the Spanish, Alpine, and Tauric centres, and believed that almost all species known from Europe had originated in one of these three, and that each of them possessed quite a distinct type of its own. This theory seems to agree very well with the facts of distribution. Let us take, for instance, the genus _Clausilia_, a pretty turret-shaped snail, which abounds on old ruined walls. Only two species, viz., _Cl. laminata_ and _Cl. bidentata_, are met with in Ireland. In England we find the same species with the addition of two others, _Cl. biplicata_ and _Cl.

Rolphii_. Crossing over the Channel to Belgium, these four species occur again, and also several others not known in England. In Germany the list of _Clausiliae_ mounts up to twenty-five species, including all those found in the British Islands. As we proceed eastward the number of species of this genus increases steadily, and when we reach the Caucasus or the Balkan Peninsula the conchologist is able to make a collection of several hundred different kinds, whilst farther east again they diminish. This clearly indicates there is in South-Eastern Europe a powerful centre of creation of _Clausiliae_, from which the species have spread all over Europe. But it is by no means certain that this centre was always in our continent, for in South-Eastern Asia and the Malay Archipelago _Clausiliae_ increase once more. It is interesting to note, however, that almost all these eastern forms belong to the sub-genus _Phaedusa_ (_vide_ Boettger), which had only been known as a fossil genus from a few species in the Eocene and Oligocene of Southern Europe. The first centre of origin, therefore, may possibly have been in Southern Asia, and in these early Tertiary times a second centre may have become established in Southern Europe from which the sub-genus _Garnieria_ went eastward, _Macroptychia_ southward, and _Nenia_ westward across the Atlantic to South America. Only a few remnants of these primitive _Clausiliae_ are now left in Europe, such as the interesting _Cl.

(Laminifera) Pauli_.

As an example of a genus which has its centre of distribution in South-Western Europe we might take that to which our common brown garden slug belongs, viz., _Arion_. Dr. Simroth, who was the first to point out that the species of _Arion_ had spread over our continent from South-Western Europe (p. 5), is inclined to the belief that the _Arionidae_ had originated on the old land-bridge between Europe and North America, which is generally known by the name of "Atlantis." From this a branch went westward to the New World and another eastward as far as Southern Asia, but _Arion_ and a number of other genera are more or less confined to South-Western Europe. Only a few species of _Arion_ have a wide range in Europe, one of them, _A. subfuscus_, crossing the borders of our continent into Siberia. In the British Islands and in Western Germany, which are about equi-distant from the supposed creative centre of the genus, there are found five species. In France six or seven species are met with, and in Spain and Portugal about ten. Towards the east, _Arions_ diminish in number. This genus, therefore, forms part of a migration which I have designated as "Lusitanian" from _Lusitania_, the name applied by the Romans to what we now call Portugal. Another genus of slugs, _Geomalacus_, is interesting from the fact that one species occurs in the British Islands, being otherwise confined to the Lusitanian province. Parmacella, a slug-like animal bearing a tiny sh.e.l.l at the extremity of its tail, has probably likewise had its origin in this part of Europe. All this, however, will be more fully referred to in the seventh chapter, which deals with the Lusitanian fauna.

As regards the Alpine centre of origin, Dr. Kobelt considers three groups of mollusca as especially characteristic of the Alps, viz., the sub-genus _Campylaea_ of the great and widely-spread genus _Helix_, and the genera _Pomatias_ and _Zonites_. The latter, which is not to be confounded with our British _Hyalinia_ (formerly united with _Zonites_), does not extend very far south or north of the Alps. There may be others too, which owe their origin to these mountains, but most of the terrestrial mollusca are exceedingly ancient, and many genera have existed long before the Alps had made their appearance above the surface of the early Tertiary seas. It should be remembered that _Hyalinia_ and _Pupa_, both British genera, are known from carboniferous deposits in forms which closely approach those living at the present day, and in these and a great number of other instances, it is quite impossible to determine the original home of the genus.

This little digression on centres of dispersion will help us to understand in what manner the indigenous element of the European fauna joined in with the alien members as they arrived in our continent. The species confined to South-Eastern England need not necessarily have come to us from Eastern Europe or Siberia. Alpine species spread northward probably at the same time as the Siberian animals went westward. An Alpine form may therefore have joined a batch of the latter and entered England with them. Even a Lusitanian animal may have mingled with these migrants, so that all three elements may occur together in one locality.

But these are exceptions. The migrations have, as a rule, not joined to any great extent; indeed, all those naturalists who have carefully examined the problem of the origin of the European fauna, have felt that it was composed of elements which arrived at different times.

The great Russian naturalist, the late Professor Brandt, distinguished five phases in the history of the Eurasian mammalian fauna (pp.

249-254). During the first phase--an uncertain period of long duration--the mammals held intact their position in the northern half of Asia. The Mammoth, the Hairy Rhinoceros, Bison, Musk Ox, Wild Sheep, Reindeer, and perhaps Tigers, Hyaenas, etc., lived then, with numerous peculiar Rodents, under such climatic conditions, according to Brandt, that they were able to extend their range along with tree vegetation to the extreme north of the Asiatic continent. This, he thinks, seems to have been the case especially with the Reindeer, Mammoth, Rhinoceros, and Musk Ox. The second phase was characterised by the dispersion of the Northern Asiatic mammalian fauna towards Central, Southern, and Western Europe, and this period lasted until the complete extermination of the Mammoth. The third phase dates from the time when the Mammoth and the Hairy Rhinoceros had become extinct, whilst the fourth commenced with the disappearance of the Reindeer in Europe, and terminated when the Wild Ox in the feral state had become unknown. Finally, the last phase const.i.tutes the present time. Lartet held similar views, and also believed that Europe was peopled by successive migrations from Asia.

Botanists have worked at the problem of the European flora much more systematically, and our knowledge of the origin of that flora has been greatly increased within the last twenty years, chiefly by the researches of Professor Engler. More recently, detailed studies have been made in Scandinavia by Professor Blytt, in the Alps by Dr. Christ and Mr. Ball, in Germany by Professor Drude, Dr. Schulz, and many others. Dr. Schulz (p. 1) is of opinion that the great majority of the European plants have either migrated to or have originated in our continent since the beginning of the Pliocene epoch, and that the original home of the immigrants must be looked for in Asia and in Arctic America. From the latter an almost uninterrupted migration must have taken place during the greater part of Tertiary times up to the commencement of the Pliocene epoch, partly over a direct land-connection with Europe by way of Greenland, Iceland, and the Faroes, and also _via_ Spitsbergen, Franz Josef Land and Novaya Zemlya, and partly by an indirect one across the Behring Straits between Alaska and Kamtchatka.

A good deal of work still requires to be done before zoologists have acquired the same intimacy with the European fauna as botanists have with the flora. However, the view that our animals all come from Asia, as was long ago believed, has been abandoned for some time. The first to bring under the notice of naturalists the hypothesis, that there must have been two distinct migrations of northern animals to Central Europe--one from the north, and another from the east--was the late Mr.

Bogdanov. The Arctic species, of which remains have been discovered in the Pyrenees--namely, the Reindeer, Arctic Hare, Willow Grouse, etc., he thought had nothing to do with those which invaded Europe from Siberia during the Glacial period. He maintained that the former had quite a distinct origin, and came from Scandinavia (p. 26).

As I shall deal with this problem more fully in a subsequent chapter, I need only mention that I fully agree with the view expressed by Mr.

Bogdanov that two distinct migrations of northern species to Central Europe can be traced.

No one, I think, has done more in fostering a careful study of the migrations of animals than our distinguished geologist Professor Boyd Dawkins. He did not follow Bogdanov in distinguishing two Arctic migrations; however, he did more in constructing a very ingenious chart (_a_, p. 111) representing the geography of Europe during the last and most recent geological epoch--the Pleistocene--and indicating on it the probable extent, during that time, of an eastern and a southern migration of mammals. The map is very instructive, and is the first ever published giving a clear idea of a southern and an eastern migration to Europe. He believed that the migration of the southern mammals northward, took place conjunctly with the westward movement of the eastern species. Having once reached Europe, the southern species are supposed to have pa.s.sed northward in summer time, whilst the eastern forms (he calls them northern) would swing southwards. The two migrations would thus occupy, at different times of the year, the same tract of ground (_a_, p. 113). From the mingling of the remains of the Hyaena with those of the Reindeer and Hippopotamus in the Kirkdale Cavern, he infers that the former preyed upon the Reindeer at one time of the year, and on the Hippopotamus at another. He argues that in such a manner might be explained the curious mixture of northern and southern types which we find in the British pleistocene and in cave deposits.

Besides mammals, the only European animals which have received some attention with a view to a study of their origin, are the b.u.t.terflies and the Land-Snails. The entomologists who have taken up the problem have in so far scarcely produced satisfactory results, as they all seemed to be bound down to the hypothesis that practically all the b.u.t.terflies had been destroyed in Europe during the Glacial period.

Hofman, in his interesting little work, comes to the conclusion (p. 50), that only in Greece and Spain could a small remnant of the b.u.t.terflies have survived the extreme rigours of climate. Greece was at that time connected with Asia Minor, and Spain with North Africa; and the author supposes that the semi-alien fauna inhabiting these tracts was mainly responsible for the re-stocking of Southern Europe, but that the main ma.s.s of our b.u.t.terflies are post-glacial Siberian immigrants.

The work published by Messrs. Speyer deals only with the origin of the Central European b.u.t.terflies. The period during which our European species originated is not specified, but the authors believe that they had their home either in Southern Russia or Central Asia. The fact that the number of b.u.t.terflies decreases very considerably as we proceed north-westward in Europe appears to them to substantiate these views.

The apparent dislike evinced by b.u.t.terflies to the damp Atlantic Coast climate, they think, clearly indicates that they had originated in a dry and more continental climate. The history of the North European b.u.t.terflies and Moths has been carefully described by Mr. Petersen. He adopts Hofman's theory as to the almost total extinction of the Lepidoptera in Europe during the Glacial period. The chief immigration to Europe after that period is, he thinks, Siberian.

At first there appeared species which belonged to a cold climate, and which now live in elevated regions; then came forms suited to a milder climate, which established themselves on the north-easterly slopes of the Alps. The most recent addition which our continent has received from Siberia is, according to Mr. Petersen, the present Scandinavian fauna.

Scandinavia has obtained a larger number of species than the European plain, because to this last migration were added such as prefer a northern or Alpine climate.

As a contribution to the history and composition of the European fauna, by far the most important work ever published is that of Dr. Kobelt, the eminent German conchologist. Whilst the researches into the origin of the Lepidoptera, above described, have been marred by the prevalent prejudice as to the deleterious effects of a glacial climate on the b.u.t.terflies, the present author boldly works out the problem on independent lines. He shuns theories and speculations almost altogether.

His great work, as yet practically unknown, the result of a lifetime of the most painstaking labour, ranks among the most important contributions to zoogeography. I shall have frequent occasion to refer to it throughout these pages. Meanwhile some of his more remarkable conclusions may be mentioned. "Comparing all cla.s.ses of animals as to their zoogeographical importance, the highest rank must undoubtedly be accorded to the land-snails" (i., p. 7). "The Pleistocene, and with it the land and fresh-water molluscan fauna of the present day has been gradually evolved from the Tertiary one, and its roots can be traced through the Cretaceous to the Jura.s.sic epoch. During the whole of that time no sudden appearance of a new fauna can be demonstrated. Quite slowly, step by step, the Cretaceous is succeeded by the Tertiary fauna, and one after the other of the characteristic palaearctic genera appear--first the fresh-water, then the land forms" (p. 141). "The division of the North Alpine from the South Alpine fauna must be older than the Glacial period; and the present Central European fauna had already become developed from the Pliocene _in all its details of form and distribution_ before the commencement of the Ice Age" (p. 162). "We must draw the conclusion from the preceding remarks, that the present (palaearctic) molluscan fauna in its distribution is older than the Glacial period, and that the latter produced merely a retreat of the fauna from the most inhospitable regions of Europe with a subsequent re-immigration, but did not cause its destruction" (i., p. 169).

A few attempts have also been made by naturalists to trace the origin of the fauna of some smaller European areas. Thus Rutimeyer, in dealing with the mammalian fauna of Switzerland, remarks (p. 31) "that it seems certain that, in spite of many local disturbances, the continuity of generations was never interrupted throughout the whole of the Tertiary period until the present day."

An even more interesting memoir is that of Mr. Koppen on the origin of the Crimean fauna. It is only recently, according to this author, that this peninsula has become connected with Southern Russia. And it is for this reason that the Squirrel and a number of other animals, and also plants, present in Russia, are absent from the Crimea. Originally the latter probably formed a westward continuation of the Caucasus, and at that time it was surrounded by the sea on all other sides. "Much later,"

he continues, "after and in consequence of a local subsidence, the country between the Caucasus and the Crimea became interrupted. The latter existed for a long time as an island, and only much later, in recent geological times, did it become united with Southern Russia by means of the isthmus of Perekop."

There is, on the whole, a great diversity of opinion as to how the European fauna has originated; however, except in Dr. Kobelt's work, no attempt has. .h.i.therto been made to collect together all the available information, and to include in the inquiry more than one cla.s.s of animals. The little work which I venture to bring before the public will not by any means exhaust the subject, nor is our knowledge of the European fauna sufficient to give more than a mere sketch of many of the animal groups mentioned. As we have learned in the introduction, different cla.s.ses of animals are not all of equal importance in indicating the changes which have taken place in the distribution of land and water. While Dr. Kobelt is of opinion that the land-snails are by far the most important in such an inquiry, Mr. Lydekker believes that mammals afford the safest and truest indications of such changes. Mr.

Beddard puts in a claim for earthworms, as even a narrow strait of sea-water forms an insuperable barrier to their dispersion. Dr. Wallace agrees with Mr. Lydekker, and goes so far as to say (p. 74) that "whenever we find that a considerable number of the mammals of two countries exhibit distinct marks of relationship, we may be sure that an actual land-connection, or at all events an approach to within a very few miles of each other, has at one time existed." Besides the groups referred to, I claim that particular attention should be devoted to Amphibia, which, contrary to Wallace, I hold do not possess special facilities for dispersal; and also to spiders and to all wingless animals leading a subterranean life, such as some of the wood-lice, planarian worms and apterous beetles.

A thorough knowledge of the changes in the distribution of land and water is desirable in order to appreciate the extent and variations of former migrations. A study of the British fauna, for example, teaches us that the British Islands were once connected with one another and with the continent of Europe between England and France. It was Professor James Geikie, I believe, who first pointed out, many years ago, that the area now covered by the Irish Sea was formerly in all probability a fresh-water lake. This had its outlet at the southern extremity in the form of a stream into which most likely flowed the smaller rivers from the south-east of Ireland, and which was joined from the east by the Severn, and finally debouched into the Atlantic (Fig. 4). The range in the British Islands of those species which have migrated to them from the south, indicates that whilst the Atlantic Ocean had gradually crept up and flooded the area between Ireland and Wales, and had turned the fresh-water lake into a bay, communication between Scotland and Ireland was still possible. The occurrence of many Scandinavian species in Scotland which are absent on the continent of Europe, indicates that these two countries also were united formerly. Most geologists hold that such a connection, if it existed, must have broken down in Pliocene times. Professor Judd, however, has expressed his belief (p. 1008) that it still existed until after the appearance of man in Northern Europe, and that our forefathers might have been able to walk dry foot from Scotland to Norway.

[Ill.u.s.tration: Fig. 4.--Map of the British Islands and surrounding area at a time when the earlier members of the southern migration reached England. (Only some of the rivers have been indicated. The shaded parts represent water, the light land.)]

I shall also show on distributional evidence, in the fourth chapter, that until recent geological times Scandinavia was continued northward, by way of Bear Island, with Spitsbergen and probably Franz Josef Land, which islands again were joined with North Greenland and Arctic North America, and that the polar fauna and flora were able to spread on this land-connection to both America and Europe.

That Gibraltar was connected with Morocco, and Sicily with Southern Italy and Greece on the one hand, and with Tunis on the other, is more generally recognised; whilst Professor Suess has shown (vol. i., p.

442), on purely geological grounds, that the Egean Sea was dry land up till quite recently--certainly, he thinks, till after the appearance of man. This supposition enables us to understand, as will be more fully discussed in the sixth chapter, how the Oriental fauna entered Europe.

Such minor zoogeographical problems as the occurrence of the Wild Goat of Asia Minor (_Capra aegagrus_) on the islands of Crete and on some of the Cyclades now almost explain themselves. The Sea of Marmora is probably a modern formation, so that Asia Minor extended not long ago beyond the Turkish capital, but Dr. Kobelt believes that an arm of the Black Sea communicated up till recent times along the lower course of the Maritza with the Gulf of Saros. It can be shown also that Sardinia and Corsica formed part of the continent of Europe, and that their present fauna and flora reached them by migration on land.

The Russian naturalists, Brandt and Koppen, believed that at no very distant date a sea extended right across Eastern Russia from the Caspian to the Arctic Ocean, whilst Professor Boyd Dawkins expressed himself in very similar language as follows (_c_, p. 35): "Before the lowering of the temperature in Central Europe the sea had already rolled through the low country of Russia, from the Caspian to the White Sea and the Baltic, and formed a barrier to western migration to the Arctic mammals of Asia." These naturalists based their opinions on distributional evidence, but additional facts will be brought forward in the fifth chapter to substantiate these views.

These are some of the more important geographical events which will be dealt with in detail in the subsequent chapters in connection with the history of the migrations of the European fauna.

A separate chapter has been devoted to the British fauna and its origin, since it plays a very important part in the evolution of that of our continent. So essential is a thorough knowledge of this fauna, that I think it would be difficult to understand, without it, the main features of the great migrations; and I have before now expressed the opinion that the British fauna forms the key to the solution of the problem of the origin of European animals. We know that our British species came to us by land--at least the bulk of them. But we want to know what direction they came from, and at what time they arrived. When Ireland became disconnected from Great Britain, and the latter from Scandinavia and France, is another interesting problem. Professor Boyd Dawkins has indicated to us a method of the special line of research to meet such inquiries. "The absence," he says (_b_, p. xxix), "of the beaver and the dormouse from Ireland must be due to the existence of some barrier to their westward migration from the adjacent mainland, and the fact that the Alpine hare is indigenous, while the common hare is absent, implies that, so far as relates to the former animal, the barrier did not exist."

Many members of the great Siberian invasion reached England, but Ireland remained entirely free from these migrants. The a.s.sumption therefore seems not unreasonable, that the latter country at the time of their arrival was no longer joined to England. The great bulk of the Irish fauna is composed of Lusitanian, Alpine, and Oriental immigrants, and there is besides a distinctly Arctic or North American element. All these, of course, must have established themselves in Ireland before the Siberian fauna set foot in England, since it has been shown that a continuous land-surface was necessary for their migration. Owing to the perfect preservation of the remains of the Siberian migrants in recent continental deposits, the history of that migration can be clearly followed, and it is possible even to determine the date of its arrival in England--in geological language at any rate. The time of the colonisation of Ireland can be thus approximately fixed as having taken place at a period prior to the arrival of the Siberian migrants in England.

All those who have seriously studied the problems presented by our British fauna--notably the late Professor Forbes, and more recently Mr.

Carpenter and myself--are agreed that the Lusitanian element is the oldest, and that the newest is that which has come to us from the east.

The sequence of events in the British Islands was probably as follows:--The first comers were the members of that fauna which issued from South-western Europe; then came the Alpine, and at the same time probably the Arctic and the Oriental; and finally the Eastern or Siberian. The migrations of all but the last continued, uninterruptedly, for very long periods.

The study of these migrations has convinced me that, though climate was a powerful factor in the evolution or history of the European fauna, the geographical changes which took place on our continent in later Tertiary times exerted a yet stronger influence. The princ.i.p.al climatic disturbance is generally supposed to have been the so-called "Ice Age."

So firmly rooted is the conviction, among naturalists of the present day, of the enormous destruction which this period produced on our European fauna, so that all animal life practically disappeared from large areas of our continent, that it is desirable that we should now shortly review the history of that remarkable period in order to ascertain in how far these views are corroborated by facts. Frequent reference, moreover, will be made throughout this work to the theories connected with the Glacial period.