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NE PAGE General principles of zoogeography.—Faunal variation.—Faunas of isola- tion.—Relations of past and prescnt faunas.—Origination of faunas If. Areas of specific distribution.—Generie distribution.—Distribution of fam- ilies and orders.—Conterminous and discontinuous areas of distribu- tion Ill. Conditions affecting distribution.—Climate.—Food-supply.—Barriers to migration.—Migrations of mammals and birds.—Dispersal of amphib- ians and reptiles.—Dispersal of insects and mollusks . IV. Zoological regions.—Holarctic realm.—Neotropical.—Ethiopian.— Orien- tal.—Australian.—Polynesian.—Tyrrhenian, Sonoran, and Austro- Malaysian transition regions . = z 5 . - Wo Distribution of marine life.—Nature of fhe deep-sea fauna.—Oceanic pelagic fauna.—Littoral fauna.—Pelagice faunas of lakes. —Deep-lake faunas . : : - : : - - : 1 ies 55 = 09 xu CONTENTS. PART II. GEOLOGICAL DISTRIBUTION. i PAGE The succession of life.—Faunas of the different geological periods. . 138 i Appearance and disappearance of species.—Reappearance.— Extinction. — Persistence of type-structures. — Variation. — Geological breaks.— Geographical distribution.—Climatic zones.—Synchronism of geo- logical formaticns . : . : : : : : 0 ; . 181 PART Il. GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. Me The present and past distribution of individual animal groups.—Forami- nifera.—Corals. — Brachiopoda, — Mollusca generally.—Crustacea.— Insecta, Arachmida, and Myriapoda_ . é ; . C 5 . 234 Il. Distribution of the Vertebrata.—Fishes. peer aes eS —Birds. —Mammals . . . 3 ees or Pei a) tesco PARLE GEOGRAPHICAL DISTRIBUTION. E General principles of zoogeography.—Faunas of isolation.—Relations of past and present faunas. EVERYWHERE upon the surface of the earth we meet with mani- festations of animal life. The desert wastes, no less than the trop- ical jungles, the bleak ice-fields of the frozen north, and the most elevated mountain-summits—all have their faunas. The abyss of the sea, no less than its surface, contributes its quota to the animal world ; and in the atmosphere all around us, from the lowest stra- tum not unlikely to the highest, the germs of the organic universe lie everywhere scattered about. In what precise form or guise this life first manifested itself, or how inert matter became endowed with that potentiality which we recognise in vital energy, it seems hopeless to attempt to determine. True science takes cognisance of both fact and theory, but illusory speculation, whose ground- work is a simple outgrowth of the imagination, must find a rest- ing-place without its domain. No one who has paid the smallest amount of attention to the facts of nature as they present themselves can have failed to notice certain peculiarities in the way of the distribution of life, which do not always admit of an immediate or of a satisfactory inter- pretation. Why, for example, one piece of country should differ so essentially in its faunal aspects from another whose physical characteristics are practically identical with its own; why the sec- ond should differ from a third, and this, again, from a fourth—may not appear comprehensible. Nor any the more comprehensible 2 GEOGRAPHICAL DISTRIBUTION. may appear the circumstance that, in most cases, island faunas are so eminently marked out from those of continental areas. Another peculiarity in faunal distribution is presented in the fact that, while certain animal assemblages enjoy an almost limit- less or universal extension, others, again, without apparent reason, are circumscribed within limits of the opposite extreme. The trav- eller to the most distant shores not infrequently recognises objects that are familiar to him as those of his native home, although pos- sibly, in the interval of his journey, he has completely lost sight of their existence, so different might have been the creatures that successively met his gaze. ‘‘ When an Englishman travels by the nearest sea-route from Great Britain to Northern Japan, he passes by countries very unlike his own, both in aspect and natural pro- ductions. The sunny isles of the Mediterranean, the sands and date-palms of Egypt, the arid rocks of Aden, the cocoa-groves of Ceylon, the tiger-haunted jungles of Malacca and Singapore, the fertile plains and volcanic peaks of Luzon, the forest-clad mountains of Formosa, and the bare hills of China, pass successively in review ; till after a circuitous voyage of thirteen thousand miles he finds himself at Hakodadi, in Japan. He is now separated from his starting-point by the whole width of Europe and Northern Asia, by an almost endless succession of plains and mountains, arid deserts or icy plateaux, yet when he visits the interior of the coun- try he sees so many familiar natural objects that he can hardly help fancying he is close to his home. He finds the woods and fields tenanted by tits, hedge-sparrows, wrens, wagtails, larks, red- breasts, thrushes, buntings, and house-sparrows, some absolutely identical with our own feathered friends, others so closely resem- bling them that it requires a practised ornithologist to tell the differ- ence. If he is fond of insects he notices many butterflies and a host of beetles which, though on close examination they are found to be distinct from ours, are yet of the same general aspect, and seem just what might be expected in any part of Europe. There are also, of course, many birds and insects which are quite new and peculiar, but these are by no means so numerous or conspicuous as to remove the general impression of a wonderful resemblance between the productions of such remote islands as Britain and Yesso:”% * Wallace, ‘‘ Island Life,” p. 3. FAUNAL VARIATION. 3 On the other hand, a journey of only very moderate duration will frequently disclose the greatest diversity existing between con- tiguous faunas. The traveller who starts east from the African coast, and who has familiarised himself with the strange produc- tions of the African continent, its elephants, giraffes, rhinoceroses, hippopotami, lions, and antelopes, finds none of these in the island of Madagascar ; the true monkeys have also disappeared, and in their place he meets with forms of half-monkeys (lemurs), a group of animals with which he will have already become acquainted before leaving the mainland. Strange creatures, wholly unlike anything previously known to him, now arrest his attention, and he finds himself in the midst of what might be termed a peculiar fauna. Likewise, if he leave the shores of Central America or Florida for the Great Antilles, the same marked isolation of the new fauna manifests itself. The larger forms of quadrupeds, such as the jaguar, couguar, tapir, and peccary, are wholly wanting, and even among the smaller and more numerously represented mammalian types many oi the more prominent forms will be sought for in vain. On the other hand, he will make the acquaintance of entirely new groups of animals, some of which, like the Centetide, have their nearest foreign representatives in regions removed by nearly one-half the circumference of the globe. And this diversity in the faunal type is found to permeate to a greater or less extent all the individual groups, birds, reptiles, &c., of the animal king- dom. It might be rashly supposed that the distance separating the regions under comparison would sufficiently account for the pecu- liarities of their respective faunas, or the disparities separating them; but distance alone, without a special relation binding to- gether the principals between which it is supposed to act, can effect nothing. We have, indeed, seen upon what a vast extent of territory the British faunal facies is stamped, and were any further proof needed of the inefficacy of distance, pure and simple, as a prime factor in geographical distribution, we have but to transport ourselves to the Malay Archipelago, and observe how wonderfully diverse are the respective faunas on either side of the very narrow (but deep) channel separating the islands of Bali and Lombok from each other. Mysterious as these various phenomena of distribution may ap- 4 GEOGRAPHICAL DISTRIBUTION. pear, they yet have all their logical explanation. A quarter of a century ago, when the doctrine of independent creation still held sway over the minds of most naturalists, and when the organic universe was reflected in the eye of the investigator as an incon- gruous agglomeration of disjointed parts, there was, indeed, no necessity for specially accounting for the facts, since they were conceived to be such by reason of a previous ordination. Now, however, when the full value of the evolutionary process is recog- nised, and animate nature has come to be looked upon as a con- crete whole, bearing special relations to its numberless parts, each individual fact seeks its own explanation, which explanation must of necessity stand in direct harmony with some previously observed fact. When, therefore, we seek to unravel the tangle of zooge- ography, and to harmonise its apparent incongruities, we must at the outset admit that distribution, such as it is, is the outcome of definite interacting laws — laws which stand in relation to each other as absolutely as they do in any other field of action—and not a hap-hazard disposition, as some would lead us to suppose, setting all enquiry at defiance. The naturalist who in the Western Hemisphere journeys south- ward from the ice-covered fields of British America fails to notice any very sudden or marked alternation in the character of the faunas that successively meet his view. New features are being constantly added, and old ones eliminated, but the interchange is effected so gradually that it becomes dificult to determine the limitations that properly define one fauna from another. The fur- bearing animals of the far north send their representatives into regions which border the habitats of the more exclusively tropical species, or are succeeded by forms which differ but little from them. The skunk, many of whose associates are animals of a distinctively Arctic character, finds its way into Mexico, and the ermine, which penetrates to the farthest northern point reached by mammals generally, still lingers on in some of the Southern United States. The Arctic fox is succeeded by the equally abundant types of the grey and the red fox; and similarly, the polar bear is followed on the one side of the continent by the grizzly, and on the other by the black bear. Having descended into the middle temperate regions, the traveller still finds about him mostly the forms with which he has already become acquainted. But many of the more FAUNAL VARIATION. 5 familiar types have either wholly disappeared, or are fast disap- pearing. Such may be the musk-sheep, moose, stag, and reindeer, which will have left as their successors the bisons and the various species of smaller deer which range throughout the remainder of the continent. The grey wolf of the northern forests breaks up into a number of varietal forms more or less distinct from the typical one, and is carried by the coyote into the heart of Mexico. Farther to the south the traveller observes entirely new features gradually appearing. In Arkansas he possibly meets with the pec- cary, the first indigenous member of the pig family with which he will have become acquainted; in Texas, with the armadillo, the first of that group of animals, the Edentata, which, in the past and present history of the South American continent, constitutes such an important element in its faunas and, in the States adjoining the Mexican Republic, with an abundant representation of the iguanid lizards, which, by their numbers, so eminently typify the follow- ing region of the tropics. There are as yet neither monkeys, ta- pirs, nor guinea-pigs, but the first appear in Southern Mexico, the second in Central America, and the last in Venezuela or Guiana. The traveller is now in the region of the Equator, and surrounded by an association of animal forms most of which were unknown to him when he entered upon his journey, and which in many respects depart so widely from those with which he was familiar at his start- ing-point as to constitute a distinct fauna. There is no longer either wolf, fox, or catamount, beaver or musk-rat, and of the spe- cifically important group of the hares or rabbits but a single species remains, The solitary species of bear is so different from its north- ern cousins as to be regarded by some naturalists as the type of a distinct genus. The contrast between the successive faunal changes observed on the north and south journey and the faunal identity which so aston- _ ishes the traveller whose journey is directed eastward from Eng- _ land to Japan is very great. And yet if the traveller from Britain, instead of proceeding due eastward, were to shape his course a few degrees to the south, much the same kinds of changes as he noticed on his American trip would again present themselves. Along the shores of the Mediterranean he would no longer, or only at rare intervals, meet with his associates of the Arctic north; on the southern slopes of the Caucasus the tiger, and in Arabia the 6 GEOGRAPHICAL DISTRIBUTION. camel, gazelle, and ostrich, would present to him certain features of a fauna which was in the main unknown to him; in India the ele- phant, lion, and rhinoceros, and other curious denizens of the jun- gle, the python and crocodile, and the numerous birds of resplendent plumage, would probably crowd from his memory the forms of the creatures ordinarily most familiar to him, and lead a passage to the ultimate goal of his journey, Australia, where he would meet with the most singular and most distinctive fauna on the surface of the earth. Much nearer to his northern home—on opposite sides of the Mediterranean—and with much less travelling, the naturalist will discern scarcely less well-marked faunal differences or peculiarities. To account for the anomalies which the facts of distribution present is the still unsolved problem that is put before the zoogeographer. Granting, with the doctrine of evolution, that all the complex assemblages of existing animal forms are modified derivatives from previously existing forms, and that these are ultimately to be traced back to some common ancestor, it must of necessity follow that any given fauna will depend for the degree of its peculiarity, whether great or small, upon the amount of modification, relative to any other fauna, which it will have undergone. And this modification can be effected in two ways: by inherent modification of the indi- vidual types composing the fauna, and by intermixture with, or immigration from, contiguous or neighbouring faunas. In both cases, manifestly, isolation or its opposite, union of habitation, will constitute the governing factor in determining the amount of varia- tion. A region that is broadly separated from all others will, natu- rally, tend to develop a fauna distinct from any other, since the progressive modifications in its constituent faunal elements must ul- timately lead to divergence; and the greater the period of isolation the greater, of necessity, will be the amount of this divergence, or the more pronounced the faunal individualisation. Hence it is that in the greater number of the more distantly removed island groups, or in those which are separated by more or less impassable barriers from the nearest land-mass, we meet with such highly specialised faunas. The Galapagos Islands, for example, as will be more fully illustrated farther on, have a fauna very distinct from that of any part of South America, although removed from it by a distance of less than seven hundred miles. The birds are quite distinct, and so are ISLAND FAUNAS. 7 the reptiles, insects, and land mollusks. The island of St. Helena, in the South Atlantic, and the Sandwich Islands, in the North Pacific, present us with similar instances of faunal specialisation, and to a less extent, also, the group of the Azores. In the case of these last, which lie in the course of the storm-winds, a considerable intermixture has been effected with the faunas of Western Africa and Europe, for we find that by far the greater number of the resi- dent iand-birds are inhabitants of those two continents as well. The fact that there are so very few peculiar forms is proof either of a recent separation of the islands from the mainland—not sufficient time having been allowed for the development of new species—or of arecent or repeated peopling with old forms from the continents. Even irrespective of considerations connected with the physical geography or geology of the region, it would naturally be inferred, from the prevalence of in-blowing storm-winds, and the known fact that certain birds are transported hither, that the second supposi- tion is the correct one; and that this is the true explanation is proved by evidence of a very positive character furnished by some of the other groups of animals. Thus, the land-Mollusca, which in their distribution are not so readily affected by aerial currents, are eminently distinguished from those of either Europe or Africa, or of any other continental land-mass, proving in their case a long- protracted period of isolation. Further, there is not a single species of fresh-water mollusk known in the entire group! The Bermuda Islands, which are about equally distant from the mainland, occupy a nearly analogous position with respect of their fauna; that is, par- tial interchanges have been effected with the fauna of the American continent. In all these cases, necessarily, the amount of faunal specialisation will be the index of the period of isolation. Where faunal immi- gration from a foreign region takes place it not only checks the development of a newly-forming fauna, by infusing into it an ele- ment that does not properly belong there, but also prevents in a measure that variation among individuals which might otherwise obtain. The case of the bobolink of the Galapagos Islands is a well-known example of this kind. It alone, of about thirty species of land-birds inhabiting those islands, is considered to be indis- putably identical with any form occurring on the mainland; hence it is concluded that this is about the only species of South American 8 GEOGRAPHICAL DISTRIBUTION. bird that ever visits the islands, for, if the case were otherwise, it would be incredible that no more common forms should have been detected there. But the fact that the bobolink has remained abso- lutely identical with the common form of South America, whence, doubtless, most of the species of Galapagos birds have been derived, while all the other birds of the island group have undergone more or less modification since the islands were first tenanted, proves that variation in its case has been prevented by the perpetuation of nor- mal characters through interbreeding with the continental migrants. In other words, the breed has been kept true. Were the migrations of the visitors checked or interrupted, there can be little question that the island breed of bobolinks would undergo the same kind of modification which distinguishes the other birds, and which has developed in them new specific er varietal types. In the conti- nent of Australia, again, we meet with the most remarkable exam- ple of a highly specialised fauna being developed as the result of long-continued isolation. Of all the varied mammalian forms which elsewhere crowd the surface of the earth we have here but the merest trace, for, with the exception of the rodents and bats, none of the ordinary orders—Carnivora, Ungulata, Insectivora, &c.—are represented.* And even of the rodents there is but a single family, that of the mice (Muridx). On the other hand, the implacental mammals—kangaroos, wombats, duck-bill—whose only non-Aus- tralian representatives are the American family of opossums (Didel- phidee), acquire here a wonderful development, and exhibit a diver- sity of type-structure not met with in any other order of mammals. Now, the animals of this class, or such as might be considered most nearly allied to the marsupials, are the first of the Mammalia to ap- pear in geological time, and they alone have thus far been detected in any of the deposits (Triassic, Jurassic) of the middle geological period, or Mesozoic era. They constitute the most primitively or- ganised members of their class, and probably stand not far removed from what may ultimately be proved to be the bottom of the mam- malian series. In order to explain the anomalies of the Australian mammalian fauna we must have recourse to the hypothesis of isolation, for in * The Australian wild-dog, or dingo, may prove to be indigenous, in which case it would represent the Carnivora. AUSTRALIAN FAUNA.:- - 9 no other way could we satisfactorily account for the remarkable development of the marsupial types, and the almost total absence of the commoner forms that are elsewhere so abundant. The oceanic barriers have evidently prevented that diffusion of species which would otherwise have sufficed to render the Australian fauna cosmopolitan in character. That this isolation, further, of the con- tinent has been of very great duration is proved by the long period of time, dating from the Cretaceous epoch, during which the most diverse forms of mammalians have existed, and the high specialisation that its own fauna has acquired. It may appear not a little surprising, in view of what has preceded, that two groups of animals, so widely removed from the rest of the Australian mam- malian fauna as are the mice and bats, should yet constitute a part of this fauna. In the case of the bats it is not difficult to ac- count for their occurrence in the region in question, since their powers of flight have enabled them to overcome such obstacles as to other animals might have proved true barriers to migration. The mice, on the other hand, whose disposition to gnaw into, and conceal themselves among, timber of all kinds, is well known, may have found their way hither from the Asiatic continent or its ad- joining islands through the intermedium of floating masses of vege- tation. Much more inexplicable is the occurrence of the single non-Australian family of marsupials, the opossums, on the American continent, which is removed by a continuous water-way of several thousands of miles, when not a single member of the entire sub-class of implacental mammals is found on any other part of the earth’s surface outside the Australian region. The hypothesis that land connection by way of the Antarctic region at one time existed be- tween Australia and South America, and, possibly, also Africa, may or may not be true, but the evidence that has thus far been adduced tending to show that by such connection a transferrence of one section of the Marsupialia has been effected from one con- tinent to the other is certainly very slim. Yet it is by no means impossible that such may have been the case. The Edentata— armadillos, ant-eaters, pangolins—whose home is preeminently the two great continents of the Southern Hemisphere, and which barely trespass north of the Tropic of Cancer, and the struthious birds, like the rhea, ostrich, and cassowary, offer equal perplexities in the way of an explanation of their anomalous distribution with the 9 : 10 GEOGRAPHICAL DISTRIBUTION. marsupials, and they have likewise been considered to afford proof of a land connection such as has been indicated. A serious diffi- culty, however, that lies in the way of this explanation is the important fact that none of the characteristic African or South American mammals are found in Australia, for it might justly be contended that if a migration or transferrence was effected in one direction, it could have been effected in the opposite direction as well. But that such reciprocal distribution did not obtain is very nearly certain. It may, indeed, be assumed that at the time of a possible Australian migration the extremities of the southern con- tinents were not yet inhabited; but this is very unlikely. Or, it may be further assumed, with Riitimeyer, that the animals under consideration had a polar origin, and that they were distributed northward along continental lines that possibly now lie buried beneath the sea; but positive evidence in this direction is still wholly wanting. An element in the problem which very materi- ally narrows the issue is the circumstance that marsupial remains have been found in the temperate regions of the Northern Hemi- sphere, and in both Europe and North America in deposits as an- cient as the Triassic period. In this upper tract, therefore, we find a possible and more probable clue towards the explanation of the existing distribution of the animals in question ; and if it be objected that some such living forms ought still to be found in the connecting region, the fact, nevertheless, remains that they did there once exist, but have since become largely extinct. It will be evident that the key to the solution of the more marked peculiarities of modern distribution must be sought in the records of the past, for in the comparison between existing and preexisting faunas alone can we expect to determine the condi- tions upon which present faunas were established, and to ascertain the dates of their respective appearances or antiquity. In most regions of the earth’s surface a most intimate relationship links together the existing fauna and the fauna of the geological period or periods immediately preceding. The Pliocene and Post-Pliocene marine shell-fish faunas of the Western United States are practically identical with the equivalent fauna of the (modern) adjoining seas; the Post-Pliocene mammals of Britain are such as still roam about the land, although they include numerous forms which no longer exist there; in India a large proportion of the mammalian types TERTIARY FAUNAS. iil that inhabit the region are already represented in deposits of the early Pliocene period; and in Australia the abundant remains of Marsupialia amply testify to the identity of character which unites the faunas of the past and present periods. A certain amount of antiquity is thus established for the several regional faunas. The farther back in time we proceed, however, the less pronounced ap- pear the common characteristics of past and present periods; and, finally, they disappear almost altogether. Thus, the Eocene shell- fish fauna of the Atlantic coast of the United States and of France and Great Britain is very unlike that of the seas adjoining those regions at the present day, although, in a measure, it finds its ana- logue in the corresponding fauna of the eastern tropical seas. The Miocene mammals of the American continent are almost wholly unlike those which now inhabit the region, and what little simi- larity still remains completely vanishes with the animals of the more ancient Eocene period. And the same holds good with the European Tertiary fauna. Yet there are a number of existing types which in their own region can be traced through a series of progressive modifications to ancestral forms more or less unlike them, which belong to a comparatively remote geological epoch. The horse of the Old World, for example, has been traced through a number of intermediate forms to the Old Tertiary Paleotherium, one of the most abundantly represented mammalian genera of the de- posits of Western Europe. The deer of the same region finds early ancestors in the horned and hornless species which occur fossil in the Miocene deposits of France and Germany; and not unlikely the wolf and fox see their progenitors among the early members of the canine race, whose remains have been traced to the Oligocene, and not impossibly also to the Eocene period. In so far as these ani- mals are concerned, therefore, we have direct evidence of a fauna of considerable antiquity developing in place. In other cases, how- ever, evidence of a very opposite character is often presented; that is to say, faunas, or their components, are very frequently shown to be in a given region of only brief duration. Thus, although bears are very plentiful at the present time in the North American continent, they are not known to have existed there before the last geological period, the Post-Pliocene. And the same is true of the members of the ox-family (Bovide)—most of which are, indeed, not represented at all as fossils—of which North America possesses 12 GEOGRAPHICAL DISTRIBUTION. five, in the main, widely-distributed species : two antelopes, two sheep (including the musk-ox), and the bison. The question as to how these animals obtained a foothold in the region which they now inhabit, whether they originated there as derivatives from previously-existing forms, or were introduced as migrants from some land-mass lying without their domain, can only be deter- mined by a reference to the still earlier fauna of not only this, but of other regions as well. In the case of the bears, for example, no immediate ancestors of the tribe have thus far been discovered in the Western Hemisphere antedating the Post-Pliocene epoch; on the other hand, in the Eastern Hemisphere—Europe—the remains of such animals, and of the true bears themselves, are abundant in deposits of the earlier Pliocene age. Hence, the assumption appears almost unavoidable that the North American fauna received its ursine contingent from the Old World. The same may or may not be also true of the American Bovide; but the determination of this question is made difficult, or impossible, through the fact that at least two of the genera—Ovibos and Bison—occur fossil in the Post-Pliocene deposits, and there only, of both the Old and the New World, and consequently appear in the two hemispheres as being of approximately equivalent age. Yet the fact that neither goats, sheep, oxen, nor antelopes have thus far been discovered fossil on the North American continent, while their remains are suf- ficiently abundant in the deposits of Eurasia (Europe-Asia) of Post- Pliocene or even much older age, would seem to indicate that the true home of the Bovide is the Old World, whence, by gradually ' spreading, and through the facilities afforded them in the way of a northern land connection, they eventually came to occupy a con- siderable portion of the New World as well. The giant sioth-like forms, such as the Megalonyx, Megatherium, and Mylodon, which in North America are associated with the remains of animals of indisputably Post-Pliocene age, occur in South America in an older formation, the Pliocene, and thus seemingly represent an. invasion of the north from the latter continent. This conclusion appears further borne out by the circumstance that the Southern Hemi- sphere is the home of the animals of this class, and that, with scarcely a single exception (Moropus, ? Morotherium) no edentate form has thus far been discovered in any North American deposit antedating the period which represents the development of the FAUNAL MIGRATION. 13 South American forms. Similarly, the extinct proboscideans, mam- moth and mastodon, are of later date in America than in Eurasia, and are in all probability to be traced back to the latter region for the place of their birth. The countries of the Old World present to us perhaps no less direct evidence as to the origination of, or the lines of migration taken by, specific groups of organisms. The European mammalian fauna is at the present time not very unlike in its general features that of North America, but in the geological period immediately preceding the present one it numbered a host of forms wholly dif- fering from anything known to have existed in the corresponding period of American history, and, indeed, quite different from any- thing now inhabiting Europe. Such, for example, were the mam- moth, African elephant, hippopotamus, African lion, leopard, the spotted and the striped hyena, several species of rhinoceros, & , forms the greater number of which are at the present day associated with the region lying south of the Mediterranean. The question that here presents itself is one, perhaps, that cannot be fully an- swered, but yet one whose partial solution is made very nearly certain. Did this fauna become suddenly exterminated, through some agency or other, in the region inhabited by it, or did it migrate elsewhere? There can be but little doubt that both conditions took place. The mammoth and the several species of (fossil) rhinoceros are now all extinct, and there is every reason to believe that their tribes per- ished gradually, without their having accomplished much migration immediately preceding final extermination. The case is, however, different with the other forms, for the fact of their inhabiting the African continent leads one to suspect that they may have found their way thither by way of some land connection no longer remain- ing. That such a connection uniting the two continents did exist within a comparatively recent geological period, permitting of an interchange of the respective faunas, is certain, as is proved by the numerous ties which bind together the faunas of the opposite shores of the Mediterranean. The Barbary ape of the Rock of Gibraltar inhabits Morocco, while the ichneumon of Spain, the porcupine of Italy, and the fallow-deer of the south of Europe generally, are all forms inhabiting the north of Africa as well. These animals evi- dently crossed over the intervening sea by some route or other, and, as has already been stated, in comparatively recent times, otherwise 14 GEOGRAPHICAL DISTRIBUTION. while the type-forms represented on the opposing shores might have been alike, the species would have almost undoubtedly differed. Equally positive proof in this direction is furnished by the similari- ties presented in the reptile and amphibian faunas. The shallow- ness of the channel separating Spain from Morocco renders it prac- tically certain that one such connecting land-mass occupied the position of the present Straits of Gibraltar. On the other hand, the finding of remains of several species of elephant in Sicily and Malta is almost proof positive of a second connection having been formed between Italy and Tunis. An elevation of the present bed of the sea a few hundred fathoms would bring about this result. The Mediterranean would then consist of two land-locked basins. But, doubtless, many of the other islands besides Sicily and Malta were united with the mainland, for otherwise it would be impossible to explain the distribution of several modern animals, the moufflon, for example, which is found in Sardinia, Corsica, Crete, and the mountains of Greece. Granting this connection between Africa and Europe, it appears more than likely that the principal disturbing element which reacted upon the Post-Pliocene European fauna, the great northern ice-sheet and the accompanying cold of the glacial period, rather than caus- ing the complete or sudden extermination of the receding fauna, compelled it to migrate over into regions of a more congenial cli- mate. That such was the fate of many of the forms there can be no reasonable doubt. The African continent thus became stocked with its existing fauna largely from the more temperate northern regions. But there is every reason to believe that these same south- ward retreating forms were in great part primarily introduced into Europe from Africa, and over the same routes by which the later southerly migration was effected. Concerning the origin of the African fauna itself we possess little precise information. The paleontology and geology of the region are so imperfectly known that we possess as yet no basis for satisfactory deductions. The absence of sufficient data naturally renders uncertain all speculation relating to the late European fauna as well. It may be considered highly probable, however, that many of its characteristic elements have been derived from the region about India, where a considerable antiquity, extending back to the Miocene or early Pliocene period, is proved for at least a number of the more prominent types. Seve- ORIGINATION OF FAUNAS. 15 ral of the antelopes have related, and apparently ancestral, forms in the Miocene deposits of Greece (Pikermi), which also contain a form not very far removed from the giraffe (Helladotherium), and a species of true giraffe itself (Camelopardalis Attica), so that possibly a contingent of the African fauna may have been derived from this region. Whether the southern or Ethiopian portion of the continent was at one time since the introduction of the placental Mammalia completely severed from the northern part or not there are as yet no means for determining. That Madagascar at one time formed part of the continent is indisputably proved by the character of its fauna ; but that its subsequent isolation is of very ancient date is conclusively shown by the complete absence of all the more distinctive Ethiopian placental mammals. The few examples that have been cited in illustration of the appearance and disappearance of faunas are sufficient to show the character of the investigation that is open to the zoogeographer. While from the data that we now possess much can be done towards shaping our suppositions, it must be confessed that our knowledge is still much too limited to permit of very satisfactory conclusions being drawn therefrom. The principal danger that besets any in- vestigation in the direction here outlined arises from the very natural assumption that the greater antiquity in any one region over another of a given type of animal indicates its prior appearance there, and migration thence to one or more secondary regions. This assumption might be well founded if we were only half con- versant with the past paleontological histories of the regions under consideration; but where at best our knowledge is still very imper- fect, as it is in the case of Africa, Asia, and South America, it would be, to say the least, highly injudicious. For what evidence have we that animal types not yet found, or dating back only to a com- paratively recent period, might not some day be turned up in abun- dance, and in deposits of such age as to completely overthrow any deductions that may have been based upon their supposed non- occurrence? A single illustration of this kind will suffice. Pale- ontologists are in the habit of considering the camels a New World family, which by migration finally occupied the region which it now inhabits. This conclusion is based upon the circumstance that numerous cameloid forms (Pliauchenia, Procamelus, Protolabis, Poebrotherium) carry this line of animals back in the North Ameri- 16 GEOGRAPHICAL DISTRIBUTION. can continent to the early Miocene period, whereas such types are almost wholly wanting in the range of equivalent deposits of the Old World. Yet, if this is the true history of the family, it is certainly a surprising fact that the true camel itself (Camelus), which is entirely unknown on the American continent, should al- ready be found fossil in the Miocene (or older Pliocene) deposits of India. Nor is it at all unlikely that ancestral forms leading up to this type may yet be found in ities: of still older age hereafter to be discovered. 1a Areas of specific distribution.—Generic distribution.—Distribution of families and orders.—Conterminous and discontinuous areas of distribution. It is a fact of general observation that a given species of animal is so restricted in its range as to entitle the geographical area princi- pally occupied by it to be considered as its home. This home may be limited in its extent toa very narrowly circumscribed area, possibly not embracing more than a few square miles, or even less, or it may spread out to dimensions coextensive (or nearly so) with the conti- nental boundaries; or, finally, it may comprise considerable portions of two or more continental areas combined. As examples of animals having a very restricted geographical distribution may be cited the Pyrenean water-mole (Myogale Pyrenaica), a small insectivore found only in a very few localities of the northern valleys of the Pyrenees, and a species of buschbok (antelope, Cephalophus Natalensis), whose habitat is the region about Port Natal, South Africa. Arc- tomys caudata, one of the Asiatic marmots, is confined to the ele- vated valley of Gombur, in India, and to heights exceeding 12,000 feet. Of birds, whose powers for self-distribution are much more fully developed than among mammals, we have equally pointed examples of localisation. The brown-and-white cactus-wren (Cam- pylorhynchus albibrunneus) is confined exclusively to the Isthmus of Panama, where its range is also somewhat limited; the Bornean yellow-bulbul (Otocampsa montis) has only been met with on the peak of Kina-Balu, in Borneo; and the red bird-of-paradise (Para- j disea rubra) only within the narrow limits of the island of Waigiou, lying to the northwest of New Guinea. The most remarkable in- stances of localisation are probably afforded by the humming-birds, several species of which would seem to be restricted respectively to the volcanic peaks of Chimborazo and Pichincha, in the equatorial 18 GEOGRAPHICAL DISTRIBUTION. Andes, and to the extinct crater of Chiriqui, in the province of Panama, Colombia. The Loddigesia mirabilis, one of the most beautiful of the Trochilide, has been observed thus far only at Chachapoyas, in the Peruvian Andes, and even there it occurs so rarely as to have been obtained but once during the period of forty years following its first discovery.? Too much stress should not, however, be laid upon what would appear to be the absolute localisation of a species, since such sup- posed localisation is frequently only the expression of our defective knowledge in the premises. In the case of the famous South American oil-bird, or guacharo (Steatornis Caripensis), for example, which was for a long time considered to inhabit solely a cave near Caripé, in the province of Cumana, Venezuela, more recent research has revealed a comparatively broad area of distribution, which embraces Sarayacu and Caxamarca in Peru, Antioquia in Colombia, and the Island of Trinidad. The garden-mouse (Mus hortulanus), which for some twenty years was known only from the botanic gar- dens of Odessa, Russia, has been found in abundance in Kaschau and several other towns of Northern Hungary.* So, likewise, in the case of the anthropoid apes of the genus Troglodytes, which were formerly supposed to be restricted to the western regions of the African continent, but which the more recent explorations of Schweinfurth, Von Heuglin, and others have shown to inhabit East Central Africa as well. Of species having a very broad distribution—excluding such as have been transplanted through the agency of man—may be cited the African elephant, whose domain extends over the greater part of the African continent south of the Sahara Desert ; the tiger, whose habitat embraces the entire east and west extent of Asia, from the Caucasus to the Island of Saghalien; and the ermine, which is found throughout the greater portion of the temperate and boreal regions of the Northern Hemisphere. The leopard ranges over entire Africa and throughout most of Southern Asia, having, with perhaps the exception of the common European wolf, whose identity with the various forms of American wolves is conceded by many natural- ists, and some of the smaller carnivores, the most wide-spread dis- tribution of any mammalian species. There is but little question as to the identity of the North American and European species of brown-bear, Arctic fox, glutton, ermine, weasel, elk, reindeer, and DISTRIBUTION OF SPECIES. 19 beaver,® all of which have, consequently, a very extended range. The American panther or couguar (Felis concolor) inhabits the territory included between Canada and Patagonia, an extent cover- ing upwards of one hundred degrees of latitude, which probably represents the greatest north and south range of any mammal. As might naturally have been expected from the greater facili- ties for dispersion, we find many more marked instances of broad specific distribution among birds than among mammals. Indeed, when we consider with what apparent facility certain birds accom- modate themselves to the varying conditions of atmospheric pres- sure and climatic changes, and the readiness with which they trav- erse broad expanses of the oceanic waters—e. g., the North Atlantic between Ireland and Labrador—it might at first sight appear as though there ought to be, at least in many cases, no absolute limit to their distribution ; yet, from our present knowledge, it may safely be affirmed that there exist but very few species of birds which are in any way cosmopolitan. The fish-hawk (Pandion haliaétus), with probably the most extensive range of any known bird, inhabits the greater portion of all the continents, with the possible exception of Australia, where its place appears to be sup- plied by a closely-allied (and by many ornithologists considered identical) species, the P. leucocephalus. Scarcely, if at all, less extensive is the range of the common peregrine falcon (Falco com- munis or peregrinus) and the barn-owl (Strix flammea), the former of which is distributed, according to Professor Newton, from ‘‘ Port Kennedy, the most northern part of the American continent, to Tasmania, and from the shores of the Sea of Okhotsk to Mendoza, in the Argentine territory,” and the latter, according to Sharpe, over the entire world, with the exception of New Zealand, and many island groups of Oceania, Malaysia, &c. The common American raven (Corvus corax) has, likewise, a very broad distribution, its range extending from Mexico into the far north, over the whole of Europe and Northern and Central Asia, as far east as the Island of Saghalien. The fishes present scarcely less well-marked examples of broad distribution; but in such aquatic forms the physical conditions of the medium which they inhabit offer far less obstacles to a very general diffusion than are to be encountered in the case of terrestrial animals. The same holds true with other aquatic animals capable 20 GEOGRAPHICAL DISTRIBUTION. of self-locomotion, and, indeed, in the case of those pelagic forms whose dispersion or ‘‘ migration” is less a matter of volition than the result of an interaction of extraneous physical causes there would seem to be no barriers set to a practically universal distribu- tion. But here, too, Nature has set a limit to the possibilities of migration, and, therefore, even among those lower forms which might be considered best adapted for withstanding the varying physical vicissitudes of their surroundings we meet with but very few species whose distribution might be said to be in any way cosmopolitan. The free-swimming pteropods, or winged - Mol- lusca, and medusoids, although exhibiting individual examples of very broad distribution, are still more or less restricted specifi- cally to well-defined oceanic areas, whose boundaries may in a measure be dependent upon the prevalent surrounding water- currents. Shells of the Spirula Peronii, a member of the two-gilled order of cephalopods, are met with almost all over the oceanic bor- ders, as well in the temperate as in the tropical zones, but, owing to the extreme rarity of the animal itself, which has been observed, perhaps, but a half-dozen times, it is impossible to say what the exact, or even approximate, range of the species is, and, conse- quently, of how much of the area of the distribution of the shell it partakes. The common form of argonaut (Argonauta argo) is found in the tropical parts of the Atlantic, Pacific, and Indian oceans, and in the Mediterranean Sea, and it has been met with as far north in the Atlantic as the New Jersey coast, and as far south as the Cape of Good Hope. The animal might, therefore, be said to be almost cosmopolitan. It may be laid down as a fundamental law in geographical dis- tribution that the areas inhabited by a given species are continuous with each other; in other words, we do not find, except at rare intervals, and under peculiar circumstances, the same species of animal inhabiting distantly-separated localities, in the interval be- tween which no individual of the species is to be met with. Thus, in the entire range of the leopard there occurs no district of any significance where the animal may not be confidently looked for, and which would negatively tend to render its distribution discon- tinuous. And the same may be said of the hundred or more degrees of latitude prowled over by the couguar, an animal whose home is at one place the lowland forests, at another the elevated AREAS OF HABITATION, 21 mountain plateaus, and at a third the grassy savannas and rolling plains. Naturally, in the case of such animals as are dependent for their existence upon certain physical peculiarities of their en- vironment, or upon particular conditions of food and climate, we shall meet with local areas scattered through the region of dis- tribution of a given species where no individuals of that species are to be met with, an apparent discontinuity being thus _pre- sented. For instance, such denizens of the forest as the South American monkeys and the sloths will but very exceptionally be found anywhere else than in their forest homes, and, therefore, the partial destruction of this forest, or its invasion by a grassy savan- na, will tend to render the ‘‘ home ” of those animals discontinuous. Possibilities of such, or a similar, discontinuity may likewise arise in the case of the animals of the plains, marshes, and deserts, since the physical aspects of the earth’s surface are constantly subjected to vicissitudes of greater or less magnitude, and, as a matter of fact, we find numerous instances where, in an extensive range, particular animals are restricted in their habitats to certain favoured spots or localities. But in all or most of such instances a former, and comparatively recent, continuity of area, or possibility of mi- gration from one locality to another, can be proved. The chamois, whose range embraces the entire east and west extent of Southern Europe, is found almost exclusively on the higher mountain sum- mits—the Pyrenees, Alps, Carpathians, Caucasus, and the moun- tains of Greece—and would appear, therefore, to occupy several widely-removed habitats. But there can be no reasonable doubt that the peculiar distribution of this animal is the outcome of migration from a central home. The hippopotamus is found in the Nile, Niger, Senegal, and most of the larger rivers of South Africa, between which stretch vast areas where no individuals of the animal have ever been found—regions untenantable by reason -of their aridity; but here, as in the case of the chamois, there can be no doubt that a migration or diffusion did take place at a time when the physical aspects of the country were favourable for such a dispersion, and were, consequently, different from what they are at present. One of the most remarkable instances of areal dis- continuity among mammals is that exhibited by the variable hare, whose home, in the Old World, is Eurasia north of the fifty-fifth parallel of latitude. The animal reappears, after skipping the low- 22 GEOGRAPHICAL DISTRIBUTION. lands of Central Europe, in the Pyrenees, Alps, and the Bavarian Highlands, and again in the Caucasus, the last region isolated by fuily one thousand miles of non-inhabited country. Equally strik- ing examples were supposed to be afforded by the fresh-water seals of Lake Baikal and the brackish-water species of the Caspian, which were considered to be identical with the northern Phoca feetida and P. vitulina respectively, but more careful study has shown this identification to be erroneous.* The critical studies made by Mr. Seebohm of the Central and East Asiatic faunas have disclosed a number of extraordinary instances of discontinuous habitation among birds. One of these is exemplified in the case of a South European variety of the common marsh-tit (Parus palustris), which reappears in an undistinguishable guise in China, although in an intervening tract of some four thousand miles (east of Asia Minor) the variety is entirely wanting, being replaced by one or more closely related forms. Ceryle guttata, a spotted king-fisher, appears to be confined to Japan and the Himalaya Mountains, being com- pletely wanting in China; and the same is true of a species of crested eagle (Spizaétus orientalis), with the exception that its range embraces the Island of Formosa. Similarly, we have two species of birds, the rufous-breasted fly-catcher (Siphia superciliaris), and the Darjeeling wood-pigeon (Palumbus pulchricollis), which are absolutely confined to the Himalayas and the Island of Formosa. But while individual cases of species inhabiting discontinuous areas do present themselves, they are of comparatively rare occur- rence, and the general law of regional continuity may be recognised. In a region occupied by a given species of animal there is usually an area which is par excellence more thickly inhabited than any other, and which may, consequently, be termed the ‘‘ metropolis” of that specics. From this metropolis there is in most cases a radial distribution of the individuals of the species, with a thinning out towards the periphery. Distinct species of the same genus rarely have coincident geographical distributions; in other words, they rarely occupy precisely the same areas, but more generally these areas, if at all continuous, overlap each other to a greater or less extent. This fact is beautifully exemplified in the case of the American hares, which are represented by some eleven species, and about as many well-marked varieties. Commencing at the far north, we have the polar or variable hare (Lepus variabilis or L. OVERLAPPING AREAS. 20 timidus, var. Arcticus), whose range extends from the Arctic coast southward to Newfoundland, and in the interior to Fort Churchill, on Hudson’s Bay. Along its southern confines it meets and slightly overlaps the boundaries of the northern varying hare (L. Ameri- canus), which, in its several geographical varieties, is distributed from the Barren Grounds in the north southward to a zone which corresponds generally with the isotherm of 52° F. On the Atlantic coast region, the southern limit of this species appears to be Con- necticut; along the line of the Appalachian highlands, Virginia (or possibly North Carolina); and in the Rocky Mountain region, New Mexico. Lepus Americanus is found throughout the northern parts of nearly all the northern tier of States interposed between the Missouri and the Atlantic coast, and over the greater portion of this vast area of distribution, which is continued westward to the Pacific, it forms the sole representative of the family. In the south its habitat overlaps the range of the wood-hare (L. sylvati- cus), which, in its several varietal forms, is distributed along the Atlantic coast from Southern New England to Yucatan. West- ward, the range of this species extends quite, or very nearly, to the Pacific, keeping, however, to a course south of the isotherm of 45° F. The prairie-hare (L. campestris) is found in the interior region, principally between the isotherms of 56° and 36°, its range being consequently overlapped on the north by that of Lepus Americanus, and on the south by L. sylvaticus. In the South- eastern United States there are two distinct ‘species, L. palustris and L. aquaticus, which are almost exclusively confined to the marshy lowlands, and whose habitats, extending to Yucatan on the south, are partially comprised in those of the wood-hare and jackass-hare (L. callotis), the last a western species, whose range descends into the arid interior of the Republic of Mexico. Finally, we have a solitary species of South American hare (L. Brasiliensis), whose reputed range embraces a considerable portion of the con- tinent from Patagonia to Panama, continuing thence into Central America.® It frequently happens that the boundaries of a given species are sharply defined against those of another, stopping just where the others begin, and where, consequently, no overlapping takes place. Such cases of specific limitation occur where natural obstacles to a free migration are suddenly encountered, as where mountain or 24 GEOGRAPHICAL DISTRIBUTION. water barriers project themselves into a given region. Thus, it will not rarely be found that a genus of animals is represented by one or several species on one side of a long mountain-slope, and by entirely distinct species on the other. And, similarly, distinct species of a genus may be encountered on opposite sides of a river-bed, although instances of such a nature among the higher animals are probably not of very frequent occurrence. Mr. Wallace cites the case of cer- tain species of Saki monkey (Pithecia), found on either side of the Amazon River, whose range either southward or northward appears to be limited by that stream. 'The same naturalist instances among birds species of jacamar (Galbula) and trumpeter (Psophia) which exhibit a similar limitation, particularly the latter, where five dis- tinct species are relegated to as many distinct, but contiguous, geo- graphical areas, separated from each other by the Amazon and some of its tributaries (Negro, Madeira, Tocantins). Of about twelve species of armadillo (separated by some naturalists into several dis- tinct genera), most of which are inhabitants of Brazil, it would seem that not a single species is common to Brazil and the Argen- tine Republic, or the Argentine Republic and Paraguay, the Parana River, with its tributaries, evidently forming an insurmountable barrier to the passage of this animal. The Uruguay River appears in the same way to limit the eastward progression of the viscacha (Lagostomys trichodactylus), an animal allied to the chinchilla, although, as has been pointed out by Mr. Darwin, the trans-Uru- guayan plains are fully as well adapted to the animal as those of its native home. Just as the boundaries of land-animals are in many instances defined by the dominant river-courses, so, in a like manner, but in a much more marked degree, the domains of fresh-water forms are frequently circumscribed by the land surfaces bordering the waters inhabited by them. This fact is beautifully exemplified in the geo- graphical distribution of two American families of fluviatile mol- lusks, the Strepomatid, or American melanians, and the Unionide, the fresh-water mussels, where the species of several genera, at least in the Southern United States, are restricted in their habitats to certain individual streams, to the exclusion of all others. In- deed, it would appear that even in such aquatic forms a large river may constitute an almost insuperable barrier to migration, as is shown in the case of the Strepomatide by the Mississippi (south of DISTRIBUTION OF JAYS. 20 the line of the Ohio River), which but very few members of the family have been able to surmount. According to Tryon, only one species of the family, Goniobasis sordida, is positively known to be common to the region on both sides of that great stream.° Probably no group of animals, as Mr. Wallace well observes, illustrates in a more striking manner the extreme features of specific distribution than the true jays, birds of the genus Garrulus. About fourteen species are recognised by ornithologists, whose combined domain embraces the entire east and west extent of the continent of Eurasia, from the Bay of Biscay to the Sea of Okhotsk, and also in- cludes the continental British Isles on the west, and the Japanese group on the east. Most of these species occupy independent areas of their own, or areas which but barely overlap on their contiguous borders. Thus, the common jay (Garrulus glandarius) inhabits the greater portion of the semi-continent of Europe, ranging from the Barbary States in Africa northward to about the sixty-fourth paral- lel of latitude (in Scandinavia and Russia), and east to the Ural Mountains. Along its southern border it meets the Algerian jay (G. cervicalis), a distinctly-marked species, and one having but a very limited range. On the southeast, again, its confines meet those of the black-headed jay (G. Krynicki), which occupies a somewhat cir- cular district extending some distance on all sides of the Black Sea. Contiguous with this last is the region inhabited by the Syrian jay (G. atricapillus), a species very closely allied to the preceding, whose domain extends through Syria, Palestine, and Southern Persia. North of this we have the limited area occupied by the Persian jay (G. hyrcanus), which has thus far been found only on the Elbruz Mountains. In an almost direct line east of this region, but separated from it by a considerable area where no jays are to be met with, we pass consecutively over the haunts of the black- throated jay (G. lanceolatus), from the Northwestern Himalayas, the Himalayan jay (G. bispecularis), from the Himalaya Mountains to the eastward of Cashmere, the Chinese jay (G. Sinensis), from South and Central China (and, occasionally, Japan), and the Formosan jay (G. Taivanus). The home of the Burmese jay (G. leucotis) adjoins that of the Himalayan jay on the southeast. North of the belt occupied by the species of southern jay we have a vast region —the desert area of Central Asia, with Thibet, Turkestan, Mon- golia, and Gobi—throughout the greater part of which no jays 26 GEOGRAPHICAL DISTRIBUTION. have as yet been discovered. Bounding this area on the north, and extending from beyond the Ural Mountains (Kazan) to the northern island of the Japanese group, there exists an almost continuous and comparatively broad belt which is tenanted throughout its entire extent, except where it overlaps the habitat of the common Euro- pean G. glandarius, by a solitary species, known as Brandt’s jay (G. Brandti). Finally, in the southern island of Japan there are found two species, G. Japonicus and G. Lidthi, the former of which, sin- gularly enough, is the species which is most nearly allied to the common European jay, although separated by the greatest distance from it.” Generic Distribution.—The laws governing specific distribu- tion are in considerable measure likewise applicable to the dis- tribution of genera. Thus, we have genera that are restricted to very limited areas, and, as a necessary consequence resulting from specific distribution, those whose areas are coextensive with con- tinental boundaries, or embrace portions of two or more continents; and, again, we have genera of a given family which occupy con- tiguous, overlapping, or discontinuous provinces. The localisation of a genus to an exceptionally narrowly circumscribed area, such as we have scen in the case of the species of humming-birds of the volcanic peaks of South America, can almost necessarily ob- tain only there where the number of species belonging to the genus is also exceptionally limited, or, more nearly, when the genus is coextensive with a single species. Potamogale, which comprises the single species P. velox, a singular otter-like insecti- vore of the west coast of Africa, appears to be confined to the region included between Angola and the Gaboon ; Cheeropsis, with the single species C. Liberiensis, an animal closely allied to the true hippopotamus, inhabits, as far as is yet known, only the wilds of Liberia; and, likewise, the singular carnivore constituting the genus Ailurus (A. fulgens) has been met with only in the Southeastern Himalayas. Instances of restriction are much more nu- merously presented in the case of insular than of continental faunas, ‘whether the examples be taken from the class of birds or mam- mals. Genera of very broad, or almost world-wide distribution, are of frequent occurrence, both among the lower and higher animals. Among the latter, in the class of birds, we have numerous examples GENERIC DISTRIBUTION. Par among the swimmers, waders, and birds of prey, whose range covers the greater extent of the primary divisions of the earth’s surface, and which may, consequently, be said to have a cosmo- politan distribution. Generic groups with a nearly world-wide distribution among the Mammalia are of much rarer, although of not exactly infrequent, occurrence, and if the Australian dingo, a species of wild dog, be not considered indigenous to the country which it inhabits, there would appear to be, if we except the bats, not a single altogether cosmopolitan genus among that class of ani- mals. Leaving out of consideration the continent of Australia, whose mammalian fauna is deficient in nearly all the orders of the class, we have a considerable number of genera whose range com- prises the greater portion of the habitable globe.* Thus, the mem- bers of the genus Felis (cats) are spread throughout the entire expanse of the continents of both the Eastern and the Western Hemisphere, through regions the extremes of whose temperature may be measured by probably no less than 225 degrees of the Fahrenheit scale. The genus Canis (dogs) has an almost equally broad distribution ; and the same range is exemplified in the case of the weasel genus (Mustela). Ursus, the bear, is met with throughout the greater part of the Northern Hemisphere, and in the continent of South America the genus has one or more rep- resentatives whose habitat is situated considerably to the south of the Equator.t The genus Cervus (deer), in its broader sense, has representatives in both North and South America, Europe, and Asia, with a very limited number of species (fallow-deer, stag) in Africa north of the Sahara. Discontinuous generic areas, like specific areas, are of com- paratively rare occurrence. Among the most remarkable instances of such discontinuity we have that exhibited in the case of the * The only placental animals indigenous to the Australian continent, if we exclude the rather doubtful dingo, which is by most naturalists considered to have been introduced by man, are the Cheiroptera (bats) and Rodentia, the latter represented by the family of mice (Muridw), The implacental mam- mals—kangaroos, wombats, phalangers—have, on the other hand, an extraor- dinary development. + The solitary species of bear inhabiting the continent of Africa appears to be confined to the Atlas Mountains; it constitutes the genus Helarctos of some authors (H. Crowtheri). 28 GEOGRAPHICAL DISTRIBUTION. genus Myogale, the water-mole, already referred to, which em- braces two species, one of which, M. Pyrenaica, is an inhabitant of the northern valleys of the Pyrenean chain of mountains, and the other, M. Muscovita, the plains of Southeastern Russia skirting the Don and Volga rivers. The pikas (Lagomys), small rodent animals having a rather near relationship with the hares, which are exten- sively distributed along the upper mountain heights from the Ural to Cashmere and the eastern extremity of Siberia, have a single outlier in the Rocky Mountains of North America. The members of the genus Capra—the goats and ibexes—occupy disjointed patches of territory in Europe, Asia, and Africa, mainly confined to the elevated mountain regions, such as the Pyrenees, the Sierras of Spain, the Alps, Caucasus, Himalayas, &c., the intervals between which are deficient in the wild or indigenous representatives of the genus.