Read Ebook: The History of the European Fauna by Scharff R F Robert Francis

Font size: 10 px 15 px 20 px 25 px 30 px 35 px

Background color: BlackWhiteGrayLight GrayDark GrayDim Gray

Text color: BlackWhiteGrayLight GrayDark GrayDim Gray

Apply/Save settings

Ebook has 789 lines and 100225 words, and 16 pages

BIBLIOGRAPHY 351-354

INDEX 355-364

PREFACE

Our knowledge of the present and past fauna of Europe is as yet insufficient to indicate with precision the original homes of its component elements, but I hope that the lines of research laid down here, and the method of treatment adopted, will aid zoologists and geologists in collecting materials for a more comprehensive study of the history of our animals. I trust also that a fresh impulse will be given by the publication of this book to the study of the Geographical Distribution of Species. Collectors of Beetles, Butterflies, Shells, and Fossils may derive some useful hints by its perusal and thus direct their studies, so as to add, by accuracy in observation, to our knowledge of the former geographical revolutions which have moulded our islands and continents. To geographers, a survey of some of the more important changes in the distribution of land and water in past times--based upon the composition of our fauna--will be interesting. The subject, however, is a complex one. I have ventured to indicate a suitable method of treatment, and as such this attempt to elucidate the history of the European fauna should be received.

To Sir William Flower, Mr. Lydekker, Professor Sars, and Professor Smitt, I am especially indebted for allowing me to reproduce drawings from their works, and to my friend Mr. Welch for some beautiful photographs. The Council of the Royal Irish Academy also kindly gave me permission to reprint the maps used in illustration of my paper. Professor Haddon first suggested my writing this book, and gave me many useful hints; and great assistance was rendered me by my colleague, Mr. G. H. Carpenter, in revising the proofs. To both of these kind friends I desire to acknowledge my deep sense of gratitude.

R. F. SCHARFF.

THE HISTORY OF THE EUROPEAN FAUNA.

INTRODUCTION.

Every student of natural history, whether he be interested in birds, butterflies, or shells, contributes his share of facts which help to show how the fauna of his country has originated. The capture of a Swallow-tail or of a Marbled White Butterfly in England at once furnishes material for reflection as to the reason of its absence from Scotland and Ireland. Why should the Nightingale allow its beautiful song to be heard in England, and never stray across the Channel to the sister isle or cross the borders of North Britain? Lovers of bird-life and sportsmen, who have observed the habits of the Ptarmigan in the wild mountain recesses of Scotland, are aware that nowhere else in the British Islands do we meet with this interesting member of the grouse family, and many no doubt have allowed their minds to dwell upon the causes of its singularly local distribution.

All these animals have a wide range in other parts of the world. In past times, before man began to make observations on the geographical distribution of birds and butterflies, or even before the appearance of man in Northern Europe, they may have lived all over the British Islands. For some reason or other they are perhaps dying out or withdrawing towards their original home, which may either be northward, or to the east or south. If we had some clue as to their former history from fossil evidence--or, in other words, if their remains had been preserved to us in geological deposits,--we should have less difficulty in deciding this problem. But butterflies are scarcely ever preserved in a fossil state, and birds very rarely. We know little or nothing, therefore, of their past history from direct evidence, and are obliged to trust to indirect methods of research which will be indicated later on.

Mammals and Snails tell us their story more plainly. The bones of the former and the shells of snails are easily preserved, and thus furnish us with the necessary data as to their past history, for we find them abundantly in most of the recent geological deposits. Among the mammals of the British Islands there are some instances of distribution which much resemble those I have quoted. Thus the Arctic Hare is in the British Islands confined to Ireland and to the mountains of Scotland; and if it were not for the fact that its bones have been discovered in a cave in the south-west of England, we should perhaps never have known that, formerly, it must have inhabited that country as well. Of other mammals we possess fossil and also historical evidence of their having once lived in these islands. Such are the Wolf and the Wild Boar, both of which were abundant in Great Britain and Ireland. The latter is a distinctly southern species. We assume this, because its remains have never been found in high northern latitudes; nor does it now occur in Northern Europe or Northern Asia, whilst all its nearest relatives live in sub-tropical or tropical climates. The Arctic Hare, on the contrary, has probably come to us from the north. Its remains are unknown even in Southern Europe, and the more we approach the Arctic Regions, the more abundant it becomes. Thus we have here two instances of British mammals, one of which, the Wild Boar, has died out--as it were in a southerly direction; whilst the other, the Arctic Hare, is apparently retreating towards the north.

There are also some British mammals of which we have no fossil history, at least of which no remains have as yet been found in these islands. Such a one is the Harvest Mouse . It has a somewhat restricted range in England, and only just crosses the Scottish border in the east. From the rest of Scotland and from the whole of Ireland it is absent. To judge from this distribution, in connection with the fact of its being unknown as a British fossil species, it is probably a late immigrant to England, and has not had time to spread, throughout Scotland at any rate. But it is also absent from Scandinavia, from the Spanish peninsula, from almost the whole of Italy and the Alps, as also from the Mediterranean Islands, whilst the little mouse occurs abundantly right across Siberia. We shall learn more about centres of dispersion later on; meanwhile I should mention that such a distribution indicates that the Harvest Mouse has most likely originated in the east, and has spread from there westward in recent geological times.

Conchologists have long ago been acquainted with the fact that many molluscs, for example the so-called "Stone-cutter" Snail and the "Cheese Snail" , have a very restricted range in the British Islands. Both are entirely absent from Scotland and Ireland, the Cheese Snail being confined to South-eastern England. The Stone-cutter has rather a wider range, is even known from a Welsh locality, and is met with as far north as Yorkshire. Their distribution would indicate, therefore, that while both are recent immigrants, the Cheese Snail is probably the last comer. This supposition is in so far supported by fossil evidence, as the latter is unknown in the fossil state, whilst the Stone-cutter has been described by Messrs. Kennard and Woodward as occurring in the cave deposit known as the Ichtham fissure, and also from several English pleistocene and holocene deposits. The Stone-cutter can scarcely be looked upon as a very recent immigrant in the light of this evidence, though we have no proof of its having ever had a much wider range in the British Islands than it has to-day.

Among the lichens, which so abundantly cover the rocks and trees in South-western Ireland, and which impart such a characteristic feature to the scenery, we find a beautifully spotted slug . It is a stranger to the rest of the British Islands, and indeed occurs nowhere else in Northern Europe. We have to travel as far as Northern Portugal before we again meet with it, and it is there also that its nearest relations live.

Many more similar examples might be quoted, but enough, I think, has been said to show that the British fauna is made up of several elements whose original homes may lie widely apart and in different directions. We have fossil evidence that some of the northern species, and also a few of the southern ones, have become extinct within comparatively recent times; others are apparently on the verge of extinction, whilst many not only maintain their position in the constant struggle for existence, but are even extending their range.

The problem of tracing the origin of the British fauna, or at least that of some of the more characteristic members of every section or element, appears at first a somewhat difficult task. Indeed, the means of dispersal of the various groups of animals are so different that it occurred to me it might be better to deal with the mammals, the birds, the reptiles, and so forth, all separately. This idea I have attempted to follow to some extent, with most satisfactory results. The British fauna of the present day is no doubt complex, but no more so than the fauna of the most recent of our geological deposits--the Pleistocene. However, when we go back still further and look at the earlier Tertiary remains, we find the fauna becoming less complex. Northern species disappear, and the strata are entirely filled with the remains of southern animals and plants. Geologists indeed are quite unanimous in their belief, that the fauna of the British Islands during the earlier epochs of the Tertiary Era was a southern one; that it then gradually became more temperate, until at last, in more recent times, decidedly northern forms invaded the country. These seem to have driven out--to some extent at least--the southern species; but more recently again, the southerners, reinforced by an eastern contingent, appear to have gained territory and are advancing into the area held by the northerners. The eastern invasion does not seem to have affected Ireland at all, and we find the country there divided between the southern and northern animals. We can thus roughly construct a map as I have done here, showing, by means of horizontal and sloping lines, the principal areas inhabited at the present time by the species of northern, southern, and eastern origin .

In the problems which are being discussed in this work I have often found it of advantage, in order to facilitate the comprehension of the arguments used, to give maps. Some of these represent the geographical conditions at the particular epoch referred to in the text, but they merely claim to give a general idea. There was never any intention to make them correspond with all the data of which we have geological evidence. They are what I might call "diagrammatic." In comparing them with reconstructions of former physical geography such as have been attempted from time to time, I hope geologists will therefore deal leniently with the faults I may have committed, and remember that the maps are "impressions," or "diagrams," and not faithful representations of all the geographical revolutions witnessed by some of our remote forefathers at any particular period.

Then again we have to take into consideration the fact, that whilst mammals, particularly the larger herbivores, are forced to migrate frequently owing to scarcity of food or temporary changes of climate, many of the invertebrates remain practically unaffected by either. Most of our land mollusca, for instance, are satisfied with meagre provender, and stand extremes of climate well, as long as there is sufficient moisture. As a result of their peculiar disposition, many of them, no doubt, have survived through several geological epochs, and have witnessed vast geographical revolutions in their immediate surroundings, whilst mammals are comparatively short-lived. Being driven from one country to another, and exposed to innumerable enemies, new types appear and old ones rapidly vanish; in fact, there are almost constant changes in the mammalian fauna as we pass from one epoch to another.

I have until now referred more particularly to the British fauna and the North European in general, because the history of our own animals interests us all more than those of any other European area. It is, moreover, preferable to commence our investigations into the origin of the European fauna by the study of a small district. This should, if possible, be an island. If we took a slice of the continent like France or Germany, we should find the problem more complex. Instead of choosing the British Islands, we might, however, take an island like Corsica or Sardinia. In either of these we should discover peculiarities in the composition of their fauna precisely similar to those which I have indicated to be present in the British fauna. We should find probably a more striking endemic element, which with us is so meagre that it can almost be left unnoticed; the main features, however, remain nearly the same. The fauna of both of these islands is composed of a strong southern element, of an eastern and a northern one, and in addition we have here species whose ancestors lived in Western Europe.

A terrestrial mammal like the deer can, under ordinary circumstances, only reach one part of a country from another by walking or running to it; but a beetle, such as the cockchafer, has two different modes of progression. It may walk or fly. In both, however, there is a third mode of transport--an involuntary one. The deer may be suddenly seized by a flood whilst crossing a river, and carried far away without necessarily coming to grief. The beetle in a similar manner could be transported to a distant country, or it might be caught in a whirlwind and blown hundreds of miles off.

We may thus distinguish between the natural or active and the accidental or passive means of distribution of animals. The active mode of dispersal again may be only migratory, as in most animals, or periodic and migratory, as in some birds and fishes. It is of course the tendency of every species to spread in all directions from its original home, provided it does not encounter obstacles, such as want of food, unsuitability of climate or soil, or barriers such as mountains, rivers, or the sea. Birds might be thought to be little interfered with by any of these barriers, but, as Dr. Wallace has shown, they are almost as much affected by them in their distribution as mammals are.

This then is the ordinary migratory distribution. Periodic distribution obtains with migratory birds and fishes. The annual flight of swallows to their northern summer residence comes under the heading of periodic migration or distribution, but apart from this, the swallow must seek to extend its range by the ordinary method, like every other animal. Similarly, the herring migrates periodically into shallow water to spawn, only to return again to its deeper home, where, as its numbers increase, there must be a tendency to spread. We have in these cases, therefore, both a periodic and an ordinary movement of migration.

Now, in studying the composition of a fauna, and especially its origin, it is of the utmost importance to be able to determine approximately the percentage of accidental arrivals and of the ordinary migrants--that is to say, of those which have reached the country owing to accidental distribution, and of animals which have adopted the usual course of migration. It is of all the more import to review this subject of accidental, or, as Darwin called it, "the occasional means" of distribution, as both he and Dr. Wallace have, I venture to think, somewhat over-estimated its significance. No one doubts that accidental transportal takes place, but the question is whether the accidentally transported animals arrive living and reach a spot where suitable food is procurable, and whether they are able to propagate their own species in the new locality. For it must be clear to anybody that the accidental transportal of a beetle or of a snail to a new country cannot affect its fauna or add one permanent member to it unless all these conditions are fulfilled. As a matter of fact, only exceedingly few instances are on record of man having witnessed, for example, the accidental transportal across the sea to an island of a live animal.

To mention an example, Colonel Feilden informs us that, when living on the island of Barbadoes, an alligator arrived one day on the shore, and at the same time a tree measuring 40 feet in length, which was recognised as a Demerara species, was likewise stranded. He thinks that there can be no doubt that the alligator, which was alive when it reached Barbadoes, was transported by the tree, thus covering a distance of 250 miles from the nearest land. Numerous observations on the accidental transportal of seeds and tree-trunks from one island to another, and from a continent to an island, have been recorded, and even on our own shores we may witness the occasional arrival of such vegetable products from a far distant land. On the west coast of Ireland it not unfrequently happens that large West Indian beans are stranded, and in this as well as in many other similar cases the seeds have often proved none the worse for their prolonged immersion in sea-water. That locusts are sometimes blown to great distances from the land is not so surprising, since their power of steering through the air is very limited. Darwin mentions having caught one 370 miles from the coast of Africa, and that swarms of them sometimes visited Madeira. Sir Charles Lyell relates that green rafts composed of canes and brush-wood are occasionally carried down the Parana River in South America by inundations, bearing on them the tiger, cayman, squirrels, and other quadrupeds.

The suggestion advanced by Darwin , that young snails just hatched might sometimes adhere to the feet of birds roosting on the ground and thus be transported, appears to me so extremely improbable as to be scarcely worth serious consideration. Indeed, as Darwin himself acknowledged later on, it does not help us very much to suggest possible modes of transport. What we require is direct evidence. How far we are, however, from obtaining it, may be inferred from Mr. Kew's remark , that "we have little or no actual evidence of precise modes of dispersal even for short distances on land."

A very curious statement was made by a well-known French conchologist, the late M. Bourguignat, with regard to introductions of mollusca. Whether he had any actual facts collected in support of it, I cannot say, but he maintained that species accidentally transported, with the exception of those under maritime influence, can only be acclimatised from north to south, and not from south to north--from east to west, but not from west to east .

I do not wish it to be understood that I am in any way undervaluing the great works of these distinguished naturalists. Darwin's views have had more influence in advancing Zoology than those of any man, and his fame is unassailable. Nevertheless, I feel that his theories regarding the origin of the faunas of oceanic islands require revision.

The formerly prevalent belief of the permanence of ocean basins has been shaken by the utterances of some of the greatest geologists of our day, whilst many positively assert that what is now deep sea of more than 1000 fathoms was dry land within comparatively recent geological epochs. Thus the Azores are classed by Darwin and Wallace among the oceanic islands--that is to say, among such as have received their fauna and flora by flotsam and jetsam. But Professor Neumayr believes, on geological grounds, that the Old and New Worlds were connected by a land-bridge during Tertiary times right across the Atlantic, and that the Canary Islands, Madeira, and Azores are the last remnants of this continent. This meets with the entire approbation of Dr. von Ihering, who has recently re-investigated the subject from a faunistic point of view . Take another instance of one of Wallace's most typical oceanic islands, the Galapagos Group. Their fauna and flora have recently been most thoroughly re-explored by an American expedition, the result of which, according to Dr. Baur, goes to show that these islands must have formed part of the mainland of South America at no distant date. The fauna and flora are therefore to be regarded as having reached them in the normal mode, viz., by migration on land. According to Mr. Beddard , it is difficult to see how earthworms could be transported across the sea. Floating tree-trunks have been observed far out at sea, but unless the water remained absolutely calm during the long period necessary for the drifting by currents so that no splashing occurred, the worms would probably be killed. Yet earthworms do occur on oceanic islands. It is indeed quite possible that our views with regard to the origin of the remainder of the Pacific Islands may change very materially, and once more revert to what Dr. Gould expressed nearly fifty years ago in the following words: "From a consideration of the land-shells on the Pacific Islands, it seems possible to draw some fair inferences as to the relations of the lands which once occupied the area of the Pacific Ocean, and whose mountain peaks evidently now indicate or constitute the islands with which it is now studded." Indeed Dr. von Ihering goes so far as to positively state that in his opinion the Polynesian Islands are not volcanic eruptions of the sea floor, which being without life were successively peopled from Australia and the neighbouring islands, but the remains of a great Pacific continent, which was in early mesozoic times connected with other continental land masses .

On the other hand, Mr. Simpson, who has gained considerable experience of oceanic dispersal in the West Indian region, though he acknowledges having often noticed bamboo rafts, which would be suitable in the transportal of invertebrates, nevertheless does not attach much importance to this means of distribution. "The fact," he remarks, "that the operculates form so large a proportion of the Antillean land-snail fauna, that a majority of the genera are found on two or more of the islands and the mainland, while nearly every species is absolutely restricted to a single island, appears to me to be very strong testimony in favour of a former general land connection" .

Amphibians are affected in the same manner by sea-water as slugs are. The accidental transportal of an amphibian from the mainland to an island is therefore almost inconceivable. And the presence of frogs, toads, and newts in the British Islands, in Corsica and Sardinia, indicates, if nothing else did, that all these islands were at no distant date united with the continent of Europe.

Mammals might be accidentally conveyed to islands on such rafts as have been described by Sir Charles Lyell, and there are instances on record of their having crossed short distances of sea by swimming. Elephants and also deer and pigs are good swimmers, the former having been known to swim for six hours at a stretch. "But," remarks Mr. Lydekker , "it may be assumed that about twenty miles is the utmost limit which mammals are likely to cross by swimming, even when favoured by currents. Such passages as these must, however, be of very rare occurrence, for a terrestrial mammal is not likely to take it into its head to swim straight out to sea in an unknown direction. Moreover, supposing a mammal, near to a particular island, to have arrived there by swimming, unless it happen to be a pregnant female, or unless another individual of the same species but of the opposite sex should arrive soon after , it would in due course die without being able to propagate its kind."

It certainly cannot be denied that a number of species among almost all groups of invertebrates have been unintentionally conveyed by man from Europe into foreign countries. It has been proposed by Dr. von Ihering to apply the term "cenocosmic" to those species which have become spread all over the world through artificial means, and thus to distinguish them from cosmopolitan ones which have attained a similar range naturally. The latter he calls "palincosmic" species . Many so-called cenocosmic ants are believed by Dr. von Ihering to be palincosmic. We are altogether too apt to regard cosmopolitan as synonymous with introduced, and we should hesitate before concluding that because one of our common European species occurs in Australia or South America, it must have been transported there recently by human agency. Some of our widely-distributed forms are probably of very great antiquity, and may have spread to distant lands in early Tertiary times, when a different state of the geographical conditions enabled them to do so.

I cannot quote a more appropriate instance than the molluscan fauna of Madeira. No less than thirteen of the Madeiran snails are looked upon as having been introduced from Europe by human agency, on the sole evidence that these happen to be common European species. Yet the correctness of this supposition must be questioned in face of the interesting observation made by Darwin , "that Madeira and the adjoining islet of Porto Santo possess many distinct but representative species of land-shells, some of which live in crevices of stone; and although large quantities of stone are annually transported from Porto Santo to Madeira, yet this latter island has not become colonised by the Porto Santo species. Nevertheless, both islands have been colonised by European land-shells, which no doubt had some advantage over the indigenous species." Darwin, therefore, meets the evident anomaly by suggesting that the European species are supposed to possess some advantages as colonisers. But the true explanation appears to me to lie in the supposition that the European land-shells found in the Madeiran Islands are all, or for the greater part, ancient forms which survived both there and on the continent, whilst the remainder of the forms inhabiting these islands are either such as are now extinct in Europe, or have become modified since their arrival there from the continent at a time when extensive land-connections allowed a free migration by land.

Among man's intentional introductions into a new country, no instance is better known than that of the rabbit to Australia. Rabbits are entirely confined to Europe. In their transplantation to Australia they were carried to a country with a different climate and among new surroundings. Yet the rabbits flourished, and within comparatively few years increased to such an extent as to become a burden and pest to the country. It may be remembered though, that, owing to the complete absence of small carnivores, which act with us as a check upon the too rapid increase of this rodent, the speed with which it established itself in the new surroundings is not so very surprising.

Many of the English settlers in the New World felt that America lacked the presence of our familiar birds. The homely sparrow was therefore brought over, with the result that the Agricultural Department of the United States is now devising means for its destruction, so rapid has been its increase.

Similarly, the inhabitants of Jamaica, annoyed by the great profusion of rats in their island, sent over to India for a number of mongoose. These have decimated the rats since their arrival, but they have multiplied to such an extent as to be a serious menace to the native fauna.

To give an instance nearer home, the Capercaillie was successfully introduced into Scotland in 1837. From its different centres of distribution it is spreading in all directions where sufficient cover is obtainable. But this case differs from the others very materially, in so far as this bird was formerly a native of Scotland, and only became extinct during the last century.

However, although there are many examples of undoubtedly successful introductions by human agency, quite as many, or perhaps more, unsuccessful ones might be quoted. In fact, it is by no means easy to establish a species in any new locality. Frequently it happens that the species seems to be on the increase at first, but then there is a decline, and after a few years the new plantation has entirely vanished. In other cases, the species disappears immediately after the introduction takes place, or lingers on for many years if it receives special and uninterrupted protection.

The Natterjack Toad has a very local distribution in the British Islands. In Ireland it is found only along the coast of Dingle Bay in County Kerry, where it is known among the peasantry as the Black Frog. There is no doubt about its being indigenous there, and though it has not spread beyond the very limited area of its habitat, the Irish climate cannot be said to be unsuited to its existence. Yet it seems to be extremely difficult to acclimatise it elsewhere, for though no less than sixty specimens were turned out in Phoenix Park, Dublin, about forty years ago, none of them were ever seen afterwards. They were placed in the vicinity of one of the lakes, so as to give them ample scope for breeding and developing the young, and in surroundings which were considered eminently suitable at the time.

Certain British species of vertebrates are generally looked upon as introduced species, though we cannot trace any record of their first establishment, and it is quite possible that, though there was local extinction and subsequent local re-introduction, they are truly indigenous and may never have become totally extinct. Such are, for instance, the Rabbit and the Pheasant . The latter certainly had become naturalised in England before the Norman invasion.

When we once more carefully review the evidence as to the undoubted difficulty attendant on intentional introduction of animals by human agency, placed as they often were in most suitable localities, we must feel that accidental introduction cannot play an important r?le in the making of the fauna of any country. Especially is this the case with an island fauna. Vertebrates are almost altogether excluded, and invertebrates must arrive singly as a rule, often stranded on an inhospitable and unsuitable shore. Their chances of surviving a passage by sea, of finding suitable food and shelter and a mate in order to procreate their species, appear to me infinitesimally small. Yet there may be some such cases. However, I quite agree with Mr. Andrew Murray--a high authority on geographical distribution--that "colonisation or occasional dispersal is insufficient to account for the character of the faunas and floras of oceanic islands; and I believe that the normal mode in which islands have been peopled, has been by direct continuity with the land at some former period, or by contiguity so close as to be equivalent to junction" . "That a slight intermixture," he continues, "due to Mr. Darwin's colonisation, occurs in many I am ready to admit; and from instances to be afterwards noticed, I am disposed to reckon the proportions of such intermixtures in the flora, in the most favourable circumstances, at not more than two per cent. In the fauna I think it must be much less."

Mr. Murray's views, though they relate only to oceanic islands, are likewise applicable to continental islands such as our own. I think we might take the admixture in the British fauna due to occasional, including human introduction, as amounting to five per cent. It is better to take a high estimate, so as to include all the species about whose native land there might be some reasonable doubt. Now of what importance, after all, is this five per cent.? The remaining ninety-five per cent. of the species of animals belonging to the British fauna undoubtedly migrated to these islands in the normal way by land.

The conviction which has been gained by zoologists and botanists, that the British Islands once formed part of the Continent, is based on the present British fauna and flora. The remains, however, of animals which used formerly to live in these countries, such as the Mammoth, the Irish Elk, the Cave Bear, and many others, tell us the same tale. They could not have peopled England by swimming across the Channel, or even by walking across solid ice, as has once been suggested. Nothing but a land-connection induced them to explore this country more closely, and finally to decide on settling there.

The origin of the British fauna will be discussed more in detail in the third chapter. The methods of investigation adopted, along with a general scheme of this book, will be found in the next.

The manner in which the origin of the fauna of any particular continental area can be traced is very similar to that adopted in the case of an island. Portions of the continent of Europe can be shown to have been islands in former times. Thus the Crimea, now a peninsula united to the mainland by the narrow isthmus of Perekop, must have been an island in comparatively recent times. The absence of a number of striking and familiar South Russian species of mammals and reptiles proves this to have been the case. It was probably long after the appearance of man, though before historic times, that these changes took place.

We shall learn in the subsequent chapters, that by a careful study of the fauna and flora the fact can be established, not only of the former connection of an island with a continent, but also whether such union existed within recent or more remote times. The better the fauna is known, both recent and fossil, the more precisely can the period of connection be indicated, and its duration determined.

FOOTNOTES:

The numbers in brackets throughout this work refer to the page-number in the Bibliography at the end.

A map giving its exact distribution in Ireland will be found on p. 300, and a figure of the slug on p. 298.

PRELIMINARY CONSIDERATIONS.

I intend to give in this chapter a general outline of the subject which will be discussed in the subsequent ones. This will include a brief history of the great events, in recent geological times, which have modified the evolution of the European fauna by the influence which they have exerted on the course of the successive streams of migration.

Share on: WhatsApp @Hash Facebook Tweet