TO GUAG RAE Aa UAL) Rav ncnihy Sha RANA NEE eS = = ee eae sm ALBERT R. MANN LIBRARY AT CORNELL UNIVERSITY DATE DUE THE INTERNATIONAL SCIENTIFIC SERIES VOLUME LVII . THE INTERNATIONAL SCIENTIFIC SERIES. Each book complete in One Volume, 12mo, and bound in Cloth. 1. THE FORMS OF WATER IN CLOUDS AND RIVERS, ICE AND GLA- CIERS. By J. Tynpau, LL. D., F.R. 8. With 35 Illustrations. $1.50. 2. PHYSICS AND POLITICS; or, Thoughts on the Application of the Prin- ciples of ‘‘ Natural Selection’? and ‘Inheritance to Political Socicty. By Waiter Bacenor. $1.50. 8. FOODS. By Epwarp Smitu, M.D., LL.B., F. R.S. With numerous Tus- trations. $1.75. 4. MIND AND BODY: The Theories of their Relation. By ALEXANDER Ban, LL.D. With 4 Dlustrations. $1.50. 5. THE STUDY OF SOCIOLOGY. By Herpert Spencer. $1.50. 6. THE NEW CHEMISTRY. By Professor J. P. Cooke, Harvard University. With 81 Illustrations. $2.00. %. THE CONSERVATION OF ENERGY. By Batrour Stewart, M.A., LL. D,, F.R.8. With 14 Illustrations. $1.50. 8. 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APPLETON & CO., 72 Fifth Avenue. “gg oS "STVWINY JO NOILNGINLSIC S:NIYd ISH “o7a's F Palaquinu aud su0pBal-Qng ou SNODTH TVOIHAVUVOEVDONZ ‘§ 3, SPDT woppsuUv.al F773 | ih myoay unisouljota— wpDay uDipD.uyspp——— UWPDIT WUIBO—=— | Vg wujooy unidoryzg wypay 1002do0.Lj0aN~— WYDIA I4ILD1OH ——— 06 03 OF THE INTERNATIONAL SCIENTIFIC SERIES THE GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION OF ANIMALS BY ANGELO HEILPRIN PROFESSOR OF INVERTEBRATE PALEONTOLOGY AT, AND CURATOR-IN-CHARGE OF, THE ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA; PROFESSOR OF GEOLOGY AT THE WAGNER FREE INSTITUTE OF SCIENCE, PHILADELPHIA}; MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, &C. NEW YORK D. APPLETON AND COMPANY 1897 Coryricut, 1886, By D. APPLETON AND COMPANY. All rights reserved. } OES “To: QOL 101 HAL TO PROFESSOR JOSEPH LEIDY, M.D., LL. D., PRESIDENT OF THE ACADEMY OF NATURAL SCIENCES OF PHILADELPHIA, 4C., , WHOSE PROFOUND RESEARCHES HAVE SO LARGELY TENDED TO DEVELOP THE SCIENCE OF BIOLOGY, THIS VOLUME IS RESPECTFULLY DEDICATED. PREFACE. In the preparation of the following pages the author has had two objects in view: that of presenting to his readers such of the more significant facts connected with the past and present distribution of animal life as might lead to a proper conception of the relations of existing faunas; and, secondly, that of furnishing to the student a work of general refer- ence, wherein the more salient features of the geography and geology of animal forms could be sought after and readily found. The need of such a work has been frequently felt and expressed. As far as he is aware, no work of that kind has as yet appeared, and therefore, to a certain extent, this publication stands alone in the field it is intended to cover. Necessarily, much that it embraces can be found elsewhere, and treated even at considerably greater length; but the mat- ter is not contained under a single cover, and where a special subject is expounded in extenso the treatment is usually too exhaustive to permit of immediate use by the general reader. This applies particularly to zoogeography. With reference to geological distribution there is little connectedly written— indeed, beyond what is found in text-books largely devoted to cognate subjects, practically nothing. Moreover, what little of connected literature on the subject we do possess is almost Vili PREFACE, entirely out of date, and in no way represents the present status of the science. The subject of geographical and geological distribution is so vast that no full treatment of it could be expected in the limited number of pages set apart for it in the present work. The author has, therefore, been obliged to omit, or at least largely ignore, the consideration of some of the less impor- tant animal groups, and, while recognising the deticiencies resulting from such omission, trusts that it will not detract much from the general usefulness of the publication. The plan of treatment followed in the early part of the book (geographical distribution) is largely that so admirably un- folded by Mr. Wallace, to whom, for the constant use of his works, the author is under great obligations. He also wishes to express his special indebtedness to the pioneer workers in this field, Schmarda and Murray, whose writings have laid the foundation of much of our existing knowledge in the premises. No special mention need be made of the numer- ous other authors who have contributed more or less exten- sively to the subject under consideration, and whose works have aided in the preparation of the present volume; to those, collectively, the author likewise desires to acknowledge his indebtedness. A few words need be said in relation to the zoogeographical regions that are recognised in this work, which differ essen- tially from those generally adopted by naturalists. The rea- sons for uniting the “Nearctic” and “ Palearctic” regions of zoogeographers into a single realm, designated, in accord- ance with a suggestion by Professor Alfred Newton, of Cam- bridge, the “ Holarctic,” are fully set forth in my paper “On the Value of the Nearctic as one of the Primary Zoological Regions,” published in the “‘ Proceedings of the Academy of : Natural Sciences of Philadelphia,” for December, 1882. Ob- PREFACE. ix jections by Mr. Wallace and Professor Gill to the views there formulated appear in “Nature” of March 22, and June 7, 1888, respectively, and my rejoinders to the criticisms of these gentlemen in “Nature” of April 26, and the ‘“ Proceed- ings” of the Philadelphia Academy for November, 1883. To these papers I must refer the reader for a purely technical statement of the case. The classification of the “Transition” tracts is largely that which has been proposed by Forsyth Major, in “ Kosmos” for 1884. Acapemy or Natura Sciences, Paiapeirara, October, 1886. CONTENTS. PART I. GEOGRAPHICAL DISTRIBUTION. I Goneral principles of zoogeography.—Faunal variation.—Faunas of isola- tion.— Relations of past and present faunas.—Origination of faunas . Il. Areas of specific distribution.—Generic distribution.—Distribution of fam- ilies aud orders.—Conterminous and discontinuous areas of distribu- tion a . . 7 ‘ : 7 . TI. 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. é ¥;, Distribution of marine life.—Nature of the deep-sea fauna.—Oceanic pelagic fauna.—Littoral fauza.—Pelagic faunas of lakes.—Deep-lake faunas PAGE 1 WW 35 55 . 109 xii CONTENTS. PART II. GEOLOGICAL DISTRIBUTION. L PAGE The succession of lite.—Faunas of the different gcological 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 formations . we O8 5 a ee é ‘ ‘ - 181 PART III. GEOGRAPHICAL AND GEOLOGICAL DISTRIBUTION. I. The present and past distribution of individual animal groups.—Forami- nifera.—Corals. — Brachiopoda. — Mollusca generally.—Crustacea.— Insecta, Arachnida,and Myriapoda . . . 3 . ) . ) . 2284 II. Distribution of the Vertebrata.—Fishes.—Amphibians.—Reptiles.—Birds. —Mammals . a 4 ‘ a x ‘ « ‘ % . » 287 PART I. GEOGRAPHICAL DISTRIBUTION. I. 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 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 of 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 tu 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 difficult 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 fauna; 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 importani 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. q 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 land-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 or 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 (Muride). On the other hand, the implacental mammals—kangaroos, wombats, duck-bill—whose .only non-Aus- tralian representatives are the American family of opossums (Didel- phide), 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 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 Ritimeyer, 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. 11 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-Pliocené 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 Bovidew 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 onc 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 bused 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 deposits of still older age hereafter to be discovered. IL. Areas of specific distribution. —Generic distribution.—Distribution of families and orders.—Conterminous and discontinuous areas of distribution. Ir 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 to a 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- 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 Folsanie 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 « 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 fully 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 foetida 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 species. 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. 23 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 Strepomatidx, 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. 25 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 seen 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 ; Cheropsis, 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 f GENERIC DISTRIBUTION. 27 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 becn introduced by man, are the Chciroptera (bats) and Rodentia, the latter represented by the family of mice (Muride). 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. A similar discontinuity is exhibited in the case of the snow-partridges of the genus Tetraogallus, a bird likewise partial to the elevated mountain-slopes. Numerous other instances of birds occupying discontinuous areas may be cited, and they appear particularly noticeable among families of a more or less tropical habit. Such, for example, are the jaganas (Parra), which inhabit the tropical regions of both the Old and the New World, the simi- larly distributed flamingoes (Pheenicopterus), the wood-ibises of the genus Tantalus, the gerontics (Geronticus), and the marabou storks (Mycteria). Among perching birds a most remarkable in- stance of generic discontinuity has been cited by Wallace in the case of the blue magpies (Cyanopica), which comprise two species, one of which, C. Cookei, inhabits the Spanish Peninsula, and the other, C.. cyanus, Eastern Siberia, Japan, and North China, the habitats of the two being removed from each other by an interval of fully 5,000 miles. Still more marked is the case of the bluebirds constituting the genus Sialia, all of whose members, with one exception, inhabit temperate and tropical America; a solitary form, Sialia (Grandala) ceelicolor, singularly enough, crops up again among the Himalaya Mountains, and eastward throughout the mountainous region sepa- rating China from Thibet.* The most remarkable instance of a mammalian genus occupying two widely -removed areas is fur- nished by Tapirus, the tapir, several species of which are natives of the South American continent, and one, very distinct from the others, of Malacca and Borneo, the group of animals, therefore, DISTRIBUTION OF FAMILIES. 29 appearing at localities separated from each other by nearly half of the earth’s circumference. Distribution of Families.—The restriction of families to cer- tain local areas is of comparatively rare occurrence, an almost neces- sary consequence of the number of species and genera of which they are in most cases composed. Among mammals the Cheiromyde, with one genus and one species, the aye-aye (Cheiromys Madagas- cariensis), are confined exclusively to the Island of Madagascar; the Protelidx, likewise consisting of but a single genus and species, the aard-wolf (Proteles Lalandii), an animal in several respects inter- mediate between the cats and dogs, and considered by some as representing a greatly modified form of hyena, are confined to the extra-tropical regions of South Africa. Occupying pretty nearly the same region, and confined to it, are the Chrysochloride, or golden-moles, with a single genus and about five species. The Ailuride, a group of animals having their nearest allies in the coatis and bears, and consisting of one or two species, appear to be restricted to the forest region of Eastern Thibet and the Eastern Himalaya. Among the class Aves we have likewise families that are restricted both as to the number of species comprised by them and the region which they inhabit. The Paictide, a group of birds, considered by some ornithologists to have affinities with the Ameri- can ant-thrushes (Formicariide), and by others with the Old-World pittas, consist of a single genus and two or more species, both of which are confined to the Island of Madagascar. Here, also, ex- clusively belong the Leptosomide, birds allied to the cuckoos and rollers. The Apterygide, with one genus (A pteryx) and four species, are strictly confined to the two larger islands of New Zealand; the Drepanide, with some four or five genera and ten species, are re- stricted to the Sandwich Island group; and, finally, the paradise- birds, excluding the bower-birds, which are classed together with them in one family by some ornithologists, with about eighteen genera and thirty species,™ are almost entirely confined to New Guinea and the surrounding islands, only four representatives of the group finding their way into the neighbouring continent of Australia. Mr. Wallace has emphasised the very remarkable case of localisation presented among reptiles by the Uropeltide, or rough-bellied, bur- rowing snakes, all of whose members appear to be strictly con- fined to Ceylon and the adjacent parts of the Peninsula of India.° 30 GEOGRAPHICAL DISTRIBUTION. Families with restricted ranges, like genera and species, are of infrequent occurrence, broad distribution being with them the rule rather than the exception. Nevertheless, owing to the peculiarily isolated position of the Australian fauna, there are among the land Mammalia only two families which can lay claim to being strictly cosmopolitan. These are the mice (Muride) among rodents, and the Vespertilionide among bats, the former being universally dis- tributed throughout the globe, if we except some of the island groups of Australasia. The Vespertilionide have representatives almost everywhere, being apparently limited, as stated by Wal- lace, only by the necessities of procuring insect food. Among birds, examples of practically cosmopolitan families are presented by the thrushes, warblers, crows, swallows, king-fishers, goatsuckers, and pigeons. The hawks, owls, ducks, and gulls are cosmopolitan por excellence, being found in almost every habitable locality throughout the globe, whether on the mainland or on the most distantly removed oceanic islands. The extensive family Fringil- lide: (finches, buntings), as now generally constituted by ornitholo- gists, with upwards of seventy genera and five hundred species, appears to have no representative in Australia, all the finch-like birds of that continent belonging to the family of the weavers (Ploceide). As with genera and species, so likewise in the case of families, we have numerous instances of groups occupying discontinuous areas. In the class of Mammalia, for example, the swine (Suide), which are so extensively distributed throughout both the tropical and temperate regions of the Old World, have no representatives in the New World north of about the thirty-fourth parallel of latitude —the Red River, in Arkansas—although they have two species (of peccary) in the region south of that line. The Orycteropodide have a solitary representative in the Cape District, the aard-vark, or Cape ant-eater (Orycteropus Capensis), and another in the interior of Northeast Africa and in Senegal, the form occurring in the latter region being possibly a third species.” The tapirs, constituting the family Tapiride, have, as already stated, their representatives on opposite sides of the globe, one species inhabiting the Malay Peninsula and some of the adjacent islands, and the four or five others the tropical forests of Central and South America. The chevrotains, or deer-like animals of the family Tragulide, abound DIVIDED FAMILIES. 31 in India and some of the islands of the Malay Archipelago, where they constitute the genus Tragulus; a solitary representative of the same family, but belonging to a distinct genus (Hyomoschus), is a native of West Africa. The anthropoid apes (Simiide) are repre- sented in Western (and probably also East Equatorial) Africa by one or more species of gorilla and chimpanzee (Troglodytes), which are almost exclusively confined to the forest region. The form most nearly allied to these man-like apes, and belonging to the same family, is the orang (Simia satyrus), which, as an inhabitant of the islands of Sumatra and Borneo, is encountered after an interval of not less than seventy dégrees of longitude. Inhabiting the same region, but with a northward extension to China, and westward to Assam (south of the Brahmaputra River), we find the members of the genus Hylobates, the gibbons. Probably the most striking example of a divided family is furnished by the Camelide, which - in the Old World are represented by the genus Camelus, with two species—the dromedary and the Bactrian camel—whose habitat extends from the Sahara through the desert regions of Western and Central Asia to Lake Baikal; and in the New World by the genus Auchenia (the Hama, alpaca, vicufia, and guanaco), with about four species, all of them restricted to the mountainous and desert regions of Western and Southern South America. We have here, therefore, a family which is not only divided by a vast ocean and the greater mass of two continents, but the members of which, in one hemi- sphere, inhabit the region north of the Equator, and, in the other, the region south of it. Instances of divided families among birds occur as in mammals, although probably to a less marked extent, owing naturally to their increased facilities for dispersion; such division obtains more espe- cially among the so-called ‘‘ tropicopolitan” forms, or those whose homes are properly the region of the tropics, or that immediately adjoining it. The flamingoes (Phenicopterid), consisting of a solitary genus and about eight speciés, are about equally distrib- uted as to the number of species throughout the warmer regions of America, Africa, and Asia, some of the forms extending their range to a considerable distance within the bounds of the Tem- perate Zone, as in Southern Europe and South America. The trogons (Trogonide), comovising many of the most beautifully- arrayed of birds, and with upwards of forty species, are more 32 GEOGRAPHICAL DISTRIBUTION. strictly confined to the tropical regions of the earth’s surface, but few forms being found beyond the limits of that zone. They are fairly abundant in the forest region of South America, ranging from Paraguay to Mexico, and less so in South and Southeast Asia, and some of the islands of the Malay Archipelago. In Af- rica the family is represented by but two species. The Psitta- cide among parrots furnish us with another good example of a divided family, whose members are to be found only in the two great southern continents, Africa and South America, and in some of the adjacent islands. Still more remarkable is the case of the ostriches, of which there are two species (of the genus Struthio) pertaining to the desert regions of Africa and Western Asia (Arabia and Syria), and likewise two (of the genus Rhea, sometimes placed in a distinct family) belonging to temperate South America, whose range extends from Patagonia to the confines of Brazil. Among reptiles similar instances are presented by the tropi- copolitan groups. Thus, we have the Crocodilidz inhabiting the tropical waters of both the Eastern and Western Hemispheres. The Pythonide, or giant constricting serpents—boas, anacondas, pythons —are, with the exception of the Californian genus Charina, some- times referred to this family, distinctively tropical, but they have representatives in the South American continent, in Africa, Asia, Australia, and in several of the continental and oceanic islands. The family of iguanas (Iguanide), comprising upwards of fifty gen- era and some three hundred species, is almost distinctively Ameri- can, being distributed from about the fiftieth parallel of south latitude, in Patagonia, to the Canadian boundary-line on the north. No member of the family is known from either of the continents of Eurasia or Africa, yet the family crops up again in a solitary genus—Brachylophus—in the Feejee Islands, and two (doubtfully placed) genera have also been described from Madagascar and Aus- tralia. Distribution of Orders.—The principal features of geographical distribution exhibited by species, genera, and families repeat them- selves in a measure in the case of the higher groups of the animal kingdom known as orders. Very narrowly circumscribed areas of habitation, at least among the orders of higher animals, do not exist; broad distribution is the rule. Among mammals the most marked instances of semi-localisation, if so it may be termed, are DISTRIBUTION OF ORDERS. 33 furnished by the Monotremata, comprising the two families of duck-bills and echidnas, both restricted to Australia and the Isl- and of Tasmania, and the Hyracoidea, an order consisting of two genera, Hyrax (the coney) and Dendrohyrax, and about a dozen species, all of which are restricted to the continent of Africa and the immediately adjoining parts of Asia (Syria). The only orders of terrestrial mammals which can lay claim to being cosmopolitan are the Cheiroptera (bats) and Rodentia, none of the other orders, except the Marsupialia—unless the dingo, as a member of the Car- nivora, be considered indigenous to the continent it now inhabits —having any representatives in Australia. Among birds we have no instance of an order being restricted to the limits of a single con- tinent. Among reptiles the Crocodilia are almost entirely confined to the tropical and sub-tropical regions, and occur in both the East- ern and Western Hemispheres. The Ophidia (serpents) have what might be called a world-wide extension, although no member of the order has been met with farther to the north than the Arctic Circle. The order Anura (frogs and toads) among amphibians is very nearly cosmopolitan ; the Urodela, on the other hand, com- prising the tailed forms, such as the newts, salamanders, &c., are almost strictly confined to the Northern Hemisphere, a few only of its representatives passing through Central America as far south as Colombia. The entire class of the Amphibia (as indigenous forms) is absent from the vast majority of oceanic islands—New Zealand, New Caledonia, and the Andaman Islands, and possibly the Solo- mon and Seychelles groups, almost alone, according to Darwin, presenting exceptional instances. The marsupials afford a remarkable example of a comparatively large order of animals occupying widely separated and discon- tinuous areas. With the exception of the opossums, of which there are two genera and about twenty species, confined to the two continents of America, and more particularly to the tropi- cal regions of these continents, all the members of this peculiar and lowly-organized order of animals are strictly limited in their range to the Australian continent and its dependent islands, and some of the islands of the Malay Archipelago. In all the broad intervening region—Europe, Africa, and Asia—no representative of the order is to be met with. The Edentata—ant-eaters, armadillos, &c.—are largely confined to the tropical and sub-tropical regions 4 34 GEOGRAPHICAL DISTRIBUTION. of South America, Asia, and Africa, and are almost completely absent from the vast northern tracts which spread out towards the polar confines, and tend to bring together the terrestrial areas of the Old and the New World. The order is entirely wanting in Europe, and nearly so in North America, the genus Tatusia, an armadillo, alone penetrating within the boundaries of the last into the State of ‘fexas. In Asia no member of the order is found to the north of the Himalaya Mountains. A remarkable example of discon- tinuous habitation among birds is furnished by the Struthiones, or ostrich-like birds, whose members are distributed throughout con- siderable reaches of tropical and sub-tropical South America, Africa, Asia, and Australia, some of the Australian islands, and New Zea- land, and are entirely wanting in Europe and North America. It is a singular circumstance in connection with the distribution of the birds of this very limited order that two genera, so closely allied as are Rhea and Struthio, should occupy areas so distantly removed from each other as Africa and South America. The Psittaci, or parrots, inhabitants of both the New and the Old World, may likewise be considered as being preeminently tropical and sub-tropical, for although a few examples are found whose range in the Southern Hemisphere ascends to the fifty-fourth degree, yet the true home of the order is located in the zone embraced be- tween the thirty-fifth parallels north and south of the Equator. Being absent from Europe and the greater portion of the continent of North America, the distribution of the order is necessarily dis- continuous. III. Conditions affecting distribution.—Climate.—Food-supply.—Barriers to mi- gration.—Migrations of mammals and birds.—Dispersal of insects and mollusks, Of the Conditions which affect or limit Distribution among Animals,—Climate.—It is a common belief that the principal fac- tor limiting or regulating the distribution of animals is constituted by climate; in other words, certain groups of animals are associated with certain grades or conditions of climate, beyond the reach of whose interacting influence they could no longer maintain an exist- ence, Thus, among quadrupeds, the elephant, camel, and tiger are popularly associated with the hottest climates of the earth’s surface ; the reindeer and moose with climates of equal, but opposite, sever- ity. And, similarly, among birds, the ostriches and hummers are considered to be particularly indicative of hot or tropical climates, and the auks, guillemots, puffins, and penguins, as products of the cold northern or southern climes. That climate does regulate dis- tribution, or impose a bar upon the migration of certain forms of life, there can be no manner of doubt; but that it does not exercise the paramount influence that is generally attributed to it there can likewise be no question. Taking, for example, some of the in- stances that have just been mentioned as indicating the supposed association between animal distribution and given conditions of climate, we find that the tiger, while its home, par ercellence, may be considered to be the hot districts of India and the Indian Archi- pelago, is in no way restricted in its range to those regions, or to regions having at all a similar climate. Thus, the animal is found in the elevated regions of the Caucasus and the Altai chain, and in the Himalaya range its footprints are not infrequently found im- pressed in the fields of snow. It is a permanent inhabitant of the 36 GEOGRAPHICAL DISTRIBUTION. cold plains of Manchuria and the Amoor region, as well as of the plains lying north of the Hindu-Kush, in Bokhara, prowling about even in winter along the icy margins of the Aral Sea. As a matter of fact, the range of the tiger extends to about the fifty-third paral- lel of north latitude—or what corresponds to the position of Lake Winnipeg, in British America—in the neighbourhood of Irkutsk and Lake Baikal. Nor can this northern range be taken to represent the range of simply stray individuals, since in the region of South- east Siberia traversed by Radde that traveller affirms that tigers were uncommonly abundant." Although at the present time the lion is confined almost exclu- sively to the tropical and sub-tropical regions of Africa and Asia, there can be but little doubt, as appears from the writings of Ilerod- otus and Aristotle, that as late as the beginning of the historic period that animal still inhabited in Europe a region lying as far north as about the fortieth parallel of latitude —or what corre- sponds in position to the State of Pennsylvania—namely, the region of Thessaly, in Greece. And even at the present day the Tunisian lion is occasionally found in the neighbourhood of the thirty-seventh parallel of north latitude, and until recently the Cape lion was abundant in or about the district of the Cape, extending to the thirty-fifth parallel of south latitude. Although the climate of these latitudes in Africa is of an unusually mild character, yet there are sudden changes of temperature, as between day and night, which may be likened to the changes in the temperature between the summer and winter climates of more temperate regions. We are informed by travellers that in the Kalahari Desert and other dry open districts of South Africa the nights are frequently unpleasant- ly cool, or even cold, the free and rapid radiation of heat from the soil not rarely being accompanied by a freezing of the surface. The formation of ice in the Desert of Sahara is, likewise, not exactly of exceptional occurrence, but in that region of the African continent, except on its immediate borders, lions are only rarely met with. That a restriction to warm climates is likewise not the case with the elephant is almost conclusively proved by the readiness with which, in the Roman period, these animals were made to pass the barrier offered by the lofty Alpine chain. Still more indisputable evidence on this point is, however, afforded by the habits of the Indian elephant, which appears to be equally at home among the CLIMATIC INFLUENCES. 37 cool mountain heights as amidst the hot and jungly lowlands. In Ceylon, according to Sir Emerson Tennent, ‘‘the mountain-tops, and not the sultry valleys, are his favorite resort. In Oovah, where the elevated plains are often crisp with the morning frost, and on Pedro-Tella-Galla, at the height of upwards of eight thousand feet, they are found in herds, whilst the hunter may search for them without success in the jungles of the low country. No altitude, in fact, seems too lofty or too chill for the elephant, provided it affords the luxury of water in abundance; and, contrary to the general opinion that the elephant delights in sunshine, he seems at all times impatient of its glare, and spends the day in the thickest depths of the forest, devoting the night to excursions, and to the luxury of the bath, in which he also indulges occasionally by day.” Mr. Johnston, during his recent explorations of the Kilimanjaro region, encountered elephants, together with buffaloes, and one or more spe- cies of antelope (kudu), at an elevation of thirteen thousand feet.%* The camel is an animal popularly associated with the burning desert regions of Africa and Asia, yet the two-humped or Bactrian species is found throughout the greater portion of Mongolia and Chinese Tartary, in the mountain region as well as in the lowlands, lying between the fortieth and fiftieth parallels of latitude, and it extends its range even considerably beyond the fiftieth parallel into Siberia, as along the borders of Lake Baikal, where it appears to pass the winter season without discomfort. It is a fact worthy of note that the only other existing representatives of the camel family —the llama and lama-like animals of the New World—are strictly adapted to a rigourous winter climate, as is shown by their partiality to the highly-elevated tracts of the South American Andes. The same adaptability to different extremes of climate likewise presents itself in the case of many of the so-called Arctic animals. The reindeer, while it habitually prefers for its home a region that en- joys a more or less rigourous climate, and where the soil is for the greater part of the year covered with snow, does not appear to be impatient of the summer heat of comparatively low latitudes. as is proved by the circumstance that in the various zoological gardens of Central Europe it not only develops in good condition, but also breeds freely. Indeed, its restriction to the high northern latitudes appears to be in no way dependent on considerations connected with either cold or snow, but merely upon the presence there in the 38 GEOGRAPHICAL DISTRIBUTION. greatest abundance of its particular food, the reindeer-moss and various lichens, without which it seems incapable of flourishing. There can be little doubt that were individuals of the reindeer transplanted to an elevated mountain region, such as the European Alps, for example, where their own proper nourishment would be again met with, they would thrive very nearly, if not fully, as well as in their true homes north of the fifty-fifth or sixtieth parallel of latitude. Indeed, even in their northern haunts the animals, at least as is shown by the American species or variety, would seem to be impatient of too great a cold, since in the winter they seek the inner recesses of the forests for protection. Turning now to the class of birds, we find that similar illustra- tions of climatic adaptation present themselves. Thus, the usually considered ‘‘tropical ” or ‘‘ equatorial” humming-birds are in reality not such at all. While it is true that by far the greater number of species belonging to this family are found within the region em- braced within the tropics, yet the range of the family extends all the way from Cape Horn (Eustephanus galeritus) to Sitka (Selas- phorus rufus), or over a territory covered by no less than one hun- dred and fifteen degrees of latitude. And even among the strictly tropical forms many of them extend their range to the limits of perpetual snow, some remaining in the cold region permanently. The Oreotrochilus Chimborazo and O. Pichincha have their abode in the equatorial peaks indicated by their respective specific names at an elevation of no less than sixteen thousand feet—or higher than the summit of the Mont Blanc—in a world of almost perpetual snow, hail, and sleet.“° In fact, the elevated Andean slopes are much more thickly visited by humming-birds than the deep low- lands, no matter how luxuriantly these last may be clothed with vegetation. The ostriches constitute another group of animals whose habitat is popularly associated with the burning deserts of the Torrid zone. While it is unquestionable that these birds do delight in just such districts, it may yet be doubted whether the matter of climate has very much to do with the selection of a region, since ostriches are, or have been until recently, equally abundant in all parts of the African continent, in the high table-lands as well as in the low- lands, from Algeria to the Cape, and from the east to the west coast, where the suitable desert conditions present themselves, and CLIMATIC INFLUENCES, 39 where, consequently, as has already been stated, the differences between the temperature of night and day are excessively marked. In the desert region of Western Asia—Persia and the Valley of the Euphrates—the bird ranges or ranged as far north as about the thirty-fifth parallel of latitude, and, indeed, it is not exactly im- probable, as has been maintained by Vambéry,™ that even at the present day it exists in limited numbers along the shores of the Sea of Aral, in about the forty-fifth parallel, or what would cor- respond to the position of the southern portion of the State of Maine. In the case of this family—Struthionide—we also notice the singular fact, analogous to that which has been observed in relation to the distribution of the Camelide, that the only repre- sentatives of the group other than Struthio (the ostrich proper), constituting the American genus Rhea, are birds belonging almost strictly to the temperate regions, their range extending from Pata- gonia to the southern confines of Brazil. The parrots (Psittaci) may be considered to be preeminently tropical birds, the vast ma- jority of the species being included in a zone bounded by the thirtieth parallel on each side of the Equator, but yet it may be doubted whether this limitation does not depend more upon the nature of the food-supply than upon the character of the climate. In South America a species of Conurus extends its range as far as the Strait of Magellan, and in the Macquarie Islands, in the South Pacific, representatives of the family are met with as high as the fifty-fourth parallel of latitude, corresponding to a position removed by only six degrees from the southern extremity of Greenland. Wallace probably justly refers to the ‘‘almost universal distribu- tion of parrots wherever the climate is sufficiently mild or uniform to furnish them with a perennial supply of food.” * But while in numerous, and perhaps the majority of, instances the limitation of animal groups to certain geographical regions is de- pendent more upon the physical character of the immediate environ- ment and the nature of the food-supply than upon particular con- ditions of climate, yet it cannot be denied that in very many cases climate appears to exercise a paramount influence upon distribution. This influence is frequently considered to be nowhere more forcibly illustrated than in the migration of birds, both as regards the northern species and those inhabiting the southern climes. That the climatic explanation of the phefiomenon of bird migration is a 40 GEOGRAPHICAL DISTRIBUTION. fallacy most ornithologists are now agreed. It is a well-ascer- tained fact that the vast majority of birds are migrants to a greater or less degree, and that non-migration with this class of animals is much more of an exception than the rule. Yet, by reason of their peculiar covering, birds generally, as compared with other vertebrates, are but slightly affected by extremes of either heat or cold, and indeed, as far as we are capable of judging, by most climatic influences, provided only that their food-supply is not affected thereby. The condor in its aerial flight within a few minutes of time accommodates itself to the most varying climatic conditions, the change from the freezing cold of the mountain heights to the scorching heat of the tropical lowland plains seem- ingly having no effect upon the vigour of the bird. There can be but little doubt, as has been insisted upon by Professor Newton, that a deficiency in the food-supply—the necessity for searching for new food—is the most obvious cause or impulse promoting bird migration. Migrations of a somewhat similar character, in- disputably governed, at least in part, by considerations connected with the food-supply, but also in greater part by conditions of climate, manifest themselves among several other classes of ani- mals. Thus, in India, the monkeys habitually ascend the Himalaya Mountains in summer to elevations of ten or twelve thousand feet, and again descend in winter. Semnopithecus schistaceus has been observed at a height of eleven thousand feet, leaping in fir-trees laden with snow wreaths! Wolves in severely cold weather descend from the mountain-slopes to the lowlands, and bears not infrequently migrate in great numbers to escape the rigours of an extreme winter. The migratory instincts of the northern hares and squirrels, and more particularly of the Norway rat and lemming, which in severe winters move in amazing numbers in direct lines over lake, river, and mountain, overcoming all obstacles that might be placed in their path, are well known. The Kamtchatka rats, under the pressure of numbers, are stated by Pennant to travel westward for a distance of eight hundred miles or more. Similar instances of the force of migration are presented by the hoofed animals. The vast herds of moving buffalo were until recently familiar sights to the traveller on the American plains; in South Africa countless numbers of antelope, impelled by the necessities of food-supply, pour down upon the more favoured districts lying without the ANIMAL MIGRATIONS. 41 region of parched soils; and similar excursions, although in this case governed by reversed thermometric conditions, are practised by the onager or wild ass of Tartary. Even the reindeer is to an extent a migrant, since in both Russia and Chinese Tartary it de- scends far southward in advance of a rigourous winter, and, indeed, frequently reaches a lower latitude than any p.irt of England, al- though in Scandinavia the animal is rarely seen south of the sixty- fifth parallel. Ti is not alone among the higher animals that the migratory in- stinct is developed. Turtles, during the ovipositing season, move in considerable numbers from one part of the sea to another, and they are stated to find their way annually to the Island of Ascen- sion. which is distant upwards of eight hundred miles from the nearest continental land-mass."* Fishes migrate in immense num- bers. but the periodical shifting of the abodes of these animals is directly connected with the processes of reproduction. Certain fishes. as the salmon, shad, and smelt, ascend the waters of fresh- water streams for the purpose of depositing their eggs: others, again, as the herring and mackerel. frequent in immense shoals, during the breeding season. the neighbourhood of the coast-line. The young eel follows the line of the river-courses in myriads, ascending all the tributary streams, and frequently overcoming apparently impassable water - falls by squirming over the moss- covered ledges on either side. Among insects, the devastating migrations of the locust are proverbial, and similar illustrations of the wandering instinct could be cited from other members of the same class of animals. A remarkable example of migration has re- cently been observed in the case of a species of grapsoid crab (Se- sarma ?) off Cape San Antonio, the western extremity of the Island of Cuba. Barriers to Migration, and Facilities for Dispersion —It has already been remarked that the interposition of extensive and elevated mountain-chains and of large bodies of water, and also sudden changes in the physical character of a country, are insur- mountable obstacles in the way of the migration or dispersion of certain classes of animals. The most serious of these obstacles. as affecting the dispersion of the Mammalia, is of course that of large bodies of water. We are well aware that the most experienced swimmer among this class of animals can accomplish by the nata- 42 GEOGRAPHICAL DISTRIBUTION. torial process but an insignificant journey, and, therefore, it would necessitate the interposition of but a very moderate expanse of water to effectually bar its progress in any given direction. Several members of the cat family are expert swimmers, the jaguar being known to cross the broadest of the South American rivers, the La Plata, as observed by Lieutenant Page. The tiger and elephant are both good swimmers. Deer are likewise prone to take to water, but it may be questioned whether animals of this kind would be apt to trust themselves beyond the sight of land. The domestic pig, even at a very young age, has been known to swim five or six miles, and it is not exactly impossible that the wild-hog, in cases of absolute necessity, might successfully attempt a passage of three or four times this distance. Probably the most remarkable exhibition of the natatorial powers of a land animal is that shown in the case of a polar bear, which was observed by Captain Parry vigourously paddling away in Barrow’s Strait at a nearest distance of twenty miles from the shore, with no ice in sight on which it could have secured needed repose. It may safely be conceded, from our present knowl- edge on the subject, that while many of the land Mammalia can effect with safety, and even readiness, such water passages as are most generally to be met with on continental areas, none, probably, would be prompted to undertake a journey across an arm of the sea whose width measured fifty or more miles, or even one much ex- ceeding half that extent.* To these difficulties or impossibilities in the way of dispersion must be attributed the circumstance that the vast number of oceanic islands are deficient, except where man has effected an introduction, in representatives of this particular class of animals. The fact that certain allied, or even identical, forms of mammals are found in regions widely removed from each other, and which at the present time are separated by impassable bodies of water of greater or less extent, is practically conclusive evi- * In the case of the polar bear above cited, the absence from view of any ice need not necessarily, or even probably, indicate that there was no ice pres- ent nearer to the swimming subject than the ice of the land-border. From the mast of a vessel, elevated one hundred and fifty feet above the surface of the water, an iceberg rising to the same height could not, owing to the curvature of the earth, be distinguished at a greater distance than thirty-four miles; flat masses of pack-ice, rising but a few feet above the water, at only about half that distance. ’ DISPERSAL OF MAMMALS. 43 dence that in the former periods of the earth’s history the surface of the globe must have undergone such vicissitudes as to have at vari- ous times disturbed the general relations existing between land and water. In other words, much of the surface that at one time was occupied by water must have been replaced by land, and, per contra, what was at one time land must at another have been water. And evidences of such variations in terrestrial equilibrium are abundantly afforded by geological landmarks. Had the greater portion of the surface of the globe at one time since the introduction of the Mam- malia consisted principally of dry land, or had there been since that period a general alternation in the relative positions of the land and water areas, the geographical distribution of the Mammalia would have been very different from what we actually find it to be. Hence, it must be assumed that a land and water alternation, such as could have brought about the present result, must have taken place in certain parts of the earth’s surface only, and without affect- ing others. There would seem to be very strong grounds for con- cluding that the most recent connection uniting the principal land- areas of the globe was formed in the Northern Hemisphere, asa belt closing off the Arctic Sea (if it then existed) from the Pacific and Atlantic oceans. The only class of terrestrial mammals’ to which a broad arm of water offers no impediment in the way of migration or disper- sion is that of the bats; and, singularly enough, just in the case of these animals, as has already been remarked, are we furnished with an example of universal distribution, there being but very few of the habitable oceanic islands which are not tenanted by one or more representatives of the order. But even among the habitually ter- restrial Mammalia there are certain exceptional methods by which dispersion to very considerable distances from the mainland can be effected. In the northern regions the frozen sea constitutes a con- necting bridge between distantly-removed land-masses which is constantly taken advantage of by various forms of Arctic animals. By the breaking up and drifting away of fragments of the northern ice-masses animals that might be temporarily wandering over them could readily be transported to very considerable distances from their true homes; and, indeed, it is through such means that polar bears are periodically stranded upon the coast of Iceland. In one year alone twelve of such wandering animals made their appearance 44 GEOGRAPHICAL DISTRIBUTION. upon the island." The reindeer is stated to cross the Behring Straits by way of the Aleutian Islands and the frozen sea, and ina somewhat similar manner the musk-ox finds its way to Melville Island; it is, however, singular that the last named, despite its long ice-journeys, never manages to reach either the continent of Asia or Greenland. In regions like the tropics, which support a luxuriant vegetable growth, and which are subject to periodical fluminal overflows, and, consequently, to the uprooting or outwashing action of the inundating waters, it not infrequently happens that islands or ‘‘rafts” of considerable magnitude, consisting mainly of inter- laced or matted vegetation—tree-trunks held together by various creepers and climbers, and containing a sufficient quantity of vege- table mould and soil bound together in the roots—are floated down stream into the open sea, where they are at once placed at the mercy of the prevailing oceanic and atmospheric currents. These rafts have been frequently noticed at the mouths of some of the larger streams, as the Mississippi, Amazon, and Ganges, and, in the case of the iast named, at a distance of a hundred miles from its mouth. Floating masses of wood, with upright trees growing over them, were mistaken by Admiral Smyth in the Philippine seas for true islands, until their motion made their real nature apparent. Such floating masses not rarely harbour various forms of animal life in their midst, and among these the Mammalia with arboreal hab- its are not inadequately represented. The South American trav- ellers Spix and Martius assert that on different occasions they ob- served monkeys, tiger-cats, squirrels, crocodiles, and a variety of birds, carried down stream (the Amazon) in this manner, and simi- lar observations have been made by other travellers in the case of the Rio Parané. It is asserted that no less than four pumas were landed in one night from such rafts in the town of Montevideo.* Some of the animals thus conveyed may travel unconcernedly, and without any special disadvantage arising from a change of abode; others, as the larger quadrupeds, will have been caught up and transported through accident. To what distance such a floating raft with its living cargo may ultimately be carried in safety, and without detriment to its inhabitants, over the oceanic surface there are as yet no data for determining. But there would appear to be no reason for assuming that they could not be transported to a distance of several hundreds of miles, seeing that the upright vege- DISPERSAL OF REPTILES. 45 tation found on many of them would serve with powerful effect in the face of a wind. And while the majority of the animal inhab- itants might be exterminated before the end of the voyage the safe arrival on an island or distant shore of a very limited number of individuals, embracing both males and females, would serve in a short period, under favourable conditions, to stock the new land with the species. That an absolute limit is set, however, to migra- tion as effected in this manner is proved conclusively by the uttcr absence in most of the oceanic islands of indigenous mammals, ex- cepting bats. The same obstacle that is interposed by the ocean to the disper- sion of the Mammalia presents itself in the case of the vast majority of other terrestrial animals in which the power of flight is not at all, or at best but feebly, developed. Thus, the serpents, although many of them are fairly good swimmers, are, if we except the marine forms, as incapable of passing oceanic barriers as are the quadrupeds, and their transportation from continental areas to regions far remote can only be effected by such or similar accidental means as that just described. As might have been expected, therefore, they are absent from nearly all oceanic islands. The Amphibia (frogs and toads) are no more fortunate in passing broad arms of the sea than are the serpents, despite the circumstance that in their young or larval condition they are strictly aquatic in their habits. Salt water proves fatal both to them and their eggs. Since moisture is a necessary condition for the early existence of this class of animals, it is evident that an extensive desert region will be an effectual barrier to their distribution—in fact, about as much so as an ocean. Lizards, in their adult condition, are as incapable of traversing an oceanic region as are the snakes and amphibians; but it would ap- pear that in some special way—whether as effected by the oceanic currents themselves or through the agency of birds—their eggs may be transported to very considerable distances out to sea, since this order of animals is sufficiently represented in remote islands where neither snakes nor amphibians have as yet been encountered. That the ocean offers no insuperable obstacle to the broad disper- sion of a very large body of birds is known from almost daily observation. Birds are known to pass several hundreds of miles on the wing without halting, and, indeed, it is not exactly im- . possible, or even improbable, that such unassisted flight may ex- 46 GEOGRAPHICAL DISTRIBUTION. tend over one or more thousands of miles. The flights of the wild-goose and the swallow have been estimated to be performed at the almost incredible velocity of from sixty to ninety miles per hour, and the flights of many of the smaller birds at not very much less. A sustained flight of ten or more hours in duration, especially when assisted by a favourable wind, involving an amount of muscular exertion probably within easy command of many birds, would carry them over an enormous stretch of territory, during a period of time which, by its brevity, would render the question of food-supply comparatively unimportant. Land-birds have been en- countered in the North Atlantic at almost all points of the oceanic expanse; but to what extent these stragglers have received assist- ance in their flight, by taking temporary shelter on board the nu- merous vessels plying between Europe and America, can hardly be determined. There is no question as to such assistance in numerous instances, but whether it is afforded in all or most cases is a matter of pure conjecture. By whatever means or methods the oceanic travel of birds may be effected, it is a matter placed beyond all ques- tion that numerous American birds make their appearance at inter- vals along the European coast. Upwards of sixty species of such foreigners, embracing examples from nearly all the orders of birds, have at different times been noted on the eastern coast of the At- lantic, principally in the British Isles and the Island of Heligoland.” Singularly enough, no distinctively European birds make their ap- pearance on the American coast, except a few whose journey over is made by way of Greenland and Iceland.* Despite the long- sustained flight of which birds are capable, it may be considered exceedingly doubtful whether many or any of them undertake these protracted journeys as a matter of their own pure choice or volition. It seems hardly possible that an animal would subject itself to such an amount of exertion and privation as would appear to be involved in journeys of this length, when no material ad- vantage could in the end be derived therefrom. It therefore ap- pears more than probable, as has been urged by Baird, Wallace, * No account is here taken of the purely pelagic forms, which are found on the opposite borders of the oceanic expanse, and which find suitable rest- ing-places on the surface of the waters. The greenshanks (Totanus glottis) has been obtained once in Florida, and apparently nowhere else in the United States. MIGRATION OF BIRDS. 4” and Newton, that the oceanic wandering of land-birds must be attributed in most, or nearly all, cases to accidental circumstances— namely, storms, or the prevalence of certain winds—which may have wafted the birds beyond their control off to sea. Winds from the west, as has been shown by Professor Baird, are preva- lent between latitudes 32° and 58° N., and, hence, would be liable to catch such birds as may be passing southward during their au- tumnal migration, especially there where their flight would be at some distance off from the shore, or across broad arms or in- lets of the sea. The dispersal would naturally be facilitated by the interaction of a heavy storm, and it is a most noteworthy confirmatory fact that the appearance of American birds on the European coast is either presaged or accompanied by heavy westerly winds blowing in that quarter. North of the fifty-eighth parallel of latitude the polar winds trend westward, and with them we have the accompanying transferrence of European birds, by way of Iceland and Greenland, to the American continent. That storms or heavy winds do influence the flight of birds in the manner here described, is indisputably proved by the facts that present them- selves in connection with the occurrence of marine birds over con- tinental areas at some distance from the shore-line. The stormy petrel, during and after the prevalence of a northeast storm, has been seen in considerable numbers in the Eastern United States beyond the Alleghany Mountains; the Thalassidroma Leachii has been abundantly killed at or about the city of Washington; and Professor Baird instances the case of a Pomarine jiger (Cataractes Pomarinus), which was killed on the Susquehanna, at Harrisburg, in 1842.” The golden plovers, in their southerly flight, start di- rect from Nova Scotia or Newfoundland for the West Indies, whence they continue their journey along the South American coast to Patagonia. In this journey but comparatively few in- dividuals touch or rest along the Atlantic States, yet it is known that during heavy northeastern winds, in the month of August, great numbers of the birds may be confidently expected along the New England coast. And it not infrequently happens that un- der similar conditions immense numbers of these and allied birds are driven to very considerable distances in the interior of the continents. In a like manner, during the prevalence of heavy storms, European birds are cast upon the Azores, situated about 48 GEOGRAPHICAL DISTRIBUTION. one thousand miles from the nearest continental coast. Among these are the kestrel, hoopoe, oriole, and snow-bunting, and not improbably also swallows, larks, and grebes.* If, then, birds may be drifted by accidental storms to a distance of one thou- sand miles in a direction contrary to that of the prevalent winds, it may be asked, Why may they not be thus drifted, at least after their first landing-place, another one thousand or two thou- sand miles further? In other words, if European birds are carried to the Azores, why are they not at intervals also transported from there to the American coast? This question can, with our present knowledge, not yet be answered. Three or four species of European birds have been noticed in the Bermuda Islands—the wheat-ear (Saxi- cola cenanthe), the sky-lark (Alauda arvensis), the snipe (Gallinago media), and the land-rail (Crex pratensis); but three of these are also found in Greenland or on the North American mainland, while the fourth, the sky-lark, appears to have been brought over in, or to have escaped from, a ship.t In an ocean studded with islands, * Most of the resident land-birds of the Azores are identical with forms found in Europe and North Africa, and it, therefore, becomes impossible to ascertain how many of the individuals actually peopling the islands may not have been recently transported from the mainland. It is only under excep- tional circumstances— barring the case of recognised stragylers—that such wanderers can be determined. + The total number of European birds known to have found their way across the Atlantic to the American shores (including Greenland) is, accord- ing to Freke (‘' Zoologist,”’ 1881), thirty-seven, of which Greenland counts about thirty, and the Eastern United States only twelve. This determination naturally excludes all birds that have been artificially introduced. Of the twelve species occurring in the Eastern United States, six are swimmers and five waders, and only one (and that somewhat doubtful, Buteo vulgaris, re- ported to have been obtained in Michigan, in October, 1878) is a true land- bird. The wheat-ear, referred to as occurring in the Bermudas, is considered a member of the North American fauna. The number of species of Amcrican birds crossing the Atlantic in the contrary direction is, according to the same authority (‘ Proc, Royal Dublin Soc.,”’ 1881), sixty-nine, of which twenty-two are swimmers, sixteen waders, and no less than thirty-one land-birds. The last include, among other forms, representatives of the genera Turdus (four species), Galeoscoptes, Regulus, Dendroeca, Hirundo, Loxia, Zonotrichia, Ceryle, Coccyzus, Picus, and several species of birds of prey. The bald- headed eagle has been recorded from Sweden. It is significant that, of the forty-seven species of waders and land-birds, only two are known from Ice- land (Falco candicans and Numenius Hudsonicus) and none from the Faroe BIRDS OF THE GALAPAGOS. 49 which afford numerous resting-places, it would not seem difficult to account for the occurrence of land-birds at the remotest dis- tances from the mainland, even without having recourse to the accessory transporting agency of prevalent winds and storms. But even with this favourable condition added. it would appear that most land-birds are not disposed to undertake of their own free will extended oceanic journeys, as is proved by the avi-fauna of many of the oceanic islands. Thus, while, as we have already seen, nearly all the representatives of the bird-fauna of the Azores, situated more than one thousand miles from the mainland, are identical with forms inhabiting either Europe or Northern Africa, indicating that the islands were peopled in comparatively recent times from those continents, in the Galapagos, situated only six hundred miles off the west coast of the continent of South Amer- ica, we meet with an entirely different state of things as regards the bird-fauna. Of about thirty species of indigenous land-birds. apparently only one, the common rice-bird (Dolichonyx oryzivorus), which ranges from Canada to Paraguay, is absolutely identical with a form found outside the limits of the island group. In addition to this a species of owl (Asio Galapagoensis) is considered by some authors to be but a mere variety of the cosmopolitan Asio brachy- otus, or short-eared owl, which is distributed from China to Ire- land, and from Greenland to Patagonia.*! We have here, there- fore, positive evidence that migrant stragglers from the South American continent are at the best of but very rare occurrence, and. on the other hand, visitors from the islands to the mainland appear to be equally rare. But since, from the resemblance which the fauna as a whole presents to that of the mainland, it is practi- cally proved that the same was at one time derived by migration from the continental areas—the islands being of volcanic origin— it is manifest that this migration must have taken place at a period sufficiently remote to have permitted the differences separating the two faunas to have been brought about. On the other hand, the absolute identity of the rice-bird with the similar form from the continent, proves. as has been pointed out by Wallace, that the island breed has been kept unaltered only through repeated or fre- Isles. The easterly dispersion is attributed to causes identical with those which have been assigned in explanation of the phenomenon by Professor 3 50 GEOGRAPHICAL DISTRIBUTION. quent visits from the specific congeners on the mainland. Not only are, with the one or two exceptions above noted, all the Galapagos land-birds specifically distinct from those found any- where else,* but they also belong largely to distinct genera. Of the fourteen genera represented, four are peculiar to the islands. The rarity of continental visitors to the Galapagos, as compared with the Azores, is to be attributed to the circumstance that these islands are situated in a zone characterised by an absence of storm winds. In the island of Juan Fernandez, situated in latitude 34° §., and only four hundred miles from the Chilian coast, there are but five species of land-birds, and of this number two are peculiar. In the Keeling or Cocos Archipelago, situated in the Indian Ocean at about the same distance from the Sumatran coast as are the Galapagos from the coast of South America, there is not a single species of true (indigenous) land-bird, although snipes and rails of the common Malayan species are sufficiently abundant; and the same is true in the case of the island of St. Helena, situated eleven hundred miles from the nearest point of the continent of Africa.t Of the twenty species of Passeres, or perching-birds, inhabiting the Sandwich Islands—about the most strictly oceanic of any group of oceanic islands so-called, being situated fully two thousand miles from the nearest continental coast-line, and the same distance from the nearest island groups (Marquesas and Aleutian), if we except the small and almost tenantless shell and coral reefs—all the forms are peculiar; and, furthermore, in all cases but one or two they belong to genera which are likewise confined to the islands. And even of the twenty-four or more species of aquatic and wading birds that have been observed on or about the islands, five—a coot (Fulica alai), a moor-hen (Gallinula Sandvichensis), a rail (Pennula Millei), and two ducks (Anas Wyvilliana and Bernicla Sandvichensis)—are peculiar.7? All in all there are some fifty species of birds known from the island group, of which about one-half are peculiar. It is evident that migrants (true land-birds) from distantly re- moved countries but rarely arrive here. In the case of the Ber- * The Dendreeca aureola, a species of wood-warbler closely allied to the “ golden’? or summer warbler of the United States (D. zstiva), is only doubt- fully separable from the D. petechia of the Island of Jamaica. + A small wading-bird of the genus Agialitis (4. Sanctee Helene), allied to a species of plover common in South Africa, is found in the island. DISPERSAL OF BIRDS AND INSECTS. 51 muda Islands, which are distant from seven hundred to eight hundred miles from the nearest coast, we meet with a different order of things. The bird-fauna of these islands consists in all of about one hundred and eighty species, including both the land and aquatic forms, of which number, however, about thirty have been noticed only on one occasion. Of the eighty-five species of land- birds less than ten are permanent residents, the rest making their way principally from the North American continent and the West India islands.** It is a singular circumstance that most of the foreign invaders are strictly migrating birds, whose course of mi- gration lies along the Atlantic coast, and which in their periodical wanderings frequently pass at some considerable distance out to sea. Entering the region of violent winds and hurricanes, they are liable to be snatched from their track, and to be forcibly trans- ported to some remote shore, where, of necessity, they will be compelled to secure for themselves a new home, and where, through frequent visitations of a like character, the original breeds estab- lished will remain pure and unaltered. Such is the condition of the bird-fauna of the Bermudas at the present time. None of the strictly non-migratory birds are represented in those islands. Two or more species of bat, also North American forms, are, with the exception of rats and mice, the only indigenous mammals. Dispersal of Insects,—It is a well-known fact that insects have been found in nearly all parts of the world that have thus far been trod by man, from the extreme limits of the Arctic and Antarctic regions to the Equator, and from the level of the sea to—and con- siderably above—the line of perpetual snow. Butterflies were ob- served by the naturalists of the ‘ Alert” and ‘‘ Discovery” nearly as far north as the eighty-third parallel of latitude; and Hum- boldt met with insects on Chimborazo, at an elevation of upwards of 18,000 feet. They are found in fresh and salt waters, freely swimming on the surface—and at very considerable distances from the mainland—as well as below it; in hot springs, where the water has attained to a moderately high temperature, and in subterranean caves. But, while the members of this class of animals, taken col- lectively, appear to be specially adapted to all the various condi- tions of existence that might be imposed upon them by accidental circumstances, the same does not hold for the individual members composing the class. Thus, certain insects are entirely dependent 52 GEOGRAPHICAL DISTRIBUTION. upon some special vegetable product for their existence, whether it be, as it may happen, the leaf, the flower, or the juice of the plant in question. Again, while in some cases the adult insect may be entirely independent of such a circumscribed food-supply, the larva may still be governed in its diet by a particular kind, without which, consequently, the prolonged reproduction of the species would be impossible. Such instances of limitation are exhibited by numerous forms of caterpillars. Hence, it is not difficult to com- prehend why, in regions which are affected by similar conditions of climate, and which collectively show a general correspondence in the character of the vegetation, certain species of insects should be found at one locality and: not at another, even where no physical barrier separating the two should be interposed. In fact, the bar- rier interposed by conditions of vegetable growth is fully as effective in restraining a broad specific distribution as are the barriers re- sulting from the physical conditions of the earth’s surface, most of which they are able to overcome, either voluntarily or involun- tarily. The mature insect, from its lightness, is frequently carried away in aerial currents from its native or favourite haunts to regions widely remote, in a manner precisely similar to what obtains in the case of birds. Hawk-moths have been caught on board ship at a distance of two hundred and fifty miles from shore, and a large Indian beetle (Chrysochroa ocellata) was captured some years ago, in the Bay of Bengal, at a distance of two hundred and seventy miles from the nearest land. During Captain King’s expedition to the Straits of Magellan dragon-flies flew on board his vessel when still fifty miles out at sea (south of the Rio de la Plata); and Admi- ral Smyth reports that, in the Mediterranean, myriads of flies were brought to his ship by a southerly wind from a region fully one hundred miles distant. A beetle is recorded by Darwin as having been caught aboard the ‘‘ Beagle” when the vessel was upwards of forty miles distant from the nearest shore; from what actual dis- tance the insect may have come could, necessarily, not be deter- mined. A locust was observed by the same naturalist three hundred and seventy miles from land; and in 1844 swarms of these insects, ‘*several miles in extent, and as thick as the flakes in a heavy snow-storm, visited Madeira. These must have come with perfect safety more than three hundred miles, and, as they continued flying over the island for a long time, they could evidently have travelled DISPERSAL OF MOLLUSKS. 53 to a much greater distance.”*4 In addition to this means of aerial dispersion, the distribution of insects may be to a great extent ef- fected in the condition of eggs, which retain a considerable amount of vitality, and which are not infrequently laid in decaying timber and in the living tissues of various plants. When, therefore, float- ing rafts or mats are apt to be formed, and to be floated out to sea, it is almost certain that with them will be carried out a host of in- sects—whether in the perfect form, as grubs, or as eggs—of different species, a fair proportion of which will, doubtless, have retained their vitality even after a protracted sea-voyage of several thousand miles. It is in this manner that many or most of the tropical forms which periodically make their appearance on the British coast have been transported thither, the current of the Gulf Stream, which trends in a general northeasterly direction, being instrumental in drifting tropical log-wood to the trans-Atlantic temperate shores. Dispersal of Mollusks.—The world-wide distribution of the fresh-water and terrestrial Mollusca, and the occurrence of identical or very nearly allied generic forms at opposite quarters of the globe, prove conclusively that the animals of this class are favoured with special instrumentalities by which a broad distribution is effected. Land-snails of the genus Helix are found in all the continental areas, from the polar regions to the Equator, and from the limit of perpetual snow on mountain summits to the level of the sea; they are also found in all the oceanic islands, even the most remote, that have thus far been visited. The exact nature of this distribution has not yet been positively determined, and, in fact, there are sev- eral difficulties in the way of accounting for it. It is well known that these animals cannot survive for any length of time the effects of salt water, and this water is almost immediately fatal to the vitality of the eggs. Hence, only under exceptional conditions is it possible to account for a transferrence over a broad expanse of oceanic surface. But it has been ascertained that such forms as are capable of secreting an epiphragm, and therewith closing up the entrance to the shell, are able to resist the injurious effects of salt water for a very considerable period, in some instances as much as two weeks, or more, as has actually been determined experimentally by the immersion of Jand-shells in the briny medium. In regard to these, therefore, there will be no difficulty in accounting for a broad distribution, since they, and especially the genus Helix of all others, 54 GEOGRAPHICAL DISTRIBUTION. would be liable to be concealed in and transported away by floating timbers, In this manner they could be drifted away for several hun- dreds of miles, and, under exceptionally favourable circumstances, to possibly one or two thousand, the more readily since some of these animals possess an enormous amount of vital tenacity, even under the most adverse conditions of existence. Thus, a Helix from North Africa (H. desertorum), contained in the British Museum collection, and glued on to a tablet, was found by the conservators to be alive after a period of more than four years. A similar in- stance of resuscitation, although after a less protracted period, has been noted in the case of one of the tabulated snails of the Acade- my of Natural Sciences of Philadelphia. Again, it has been con- clusively shown by Darwin and others that the eggs of pond and other fresh-water bivalve-mollusks are occasionally found attached to the feet of wading-birds—ducks, and the like—visiting such waters, and are by them liable to be carried to very considerable distances from their true homes, and thereby to have their range almost illimitably widened. Such a method of transport, although exer- cised to a much more limited extent, has been observed to be effect- ed even by species of water-beetle, whose legs may have become entrapped between the valves of the shell, as well as by newts and other amphibians. The broad distribution of allied or identical generic and specific forms of fluviatile mollusks over the most ex- tended or widely remote geographical areas reccives a partial ex- planation in the circumstance that the physical forces operating upon the earth’s crust, causing movements in it of a differential character—i. ¢., elevation at one point and subsidence at another— tend to destroy the permanency of river courses, turning them now to one side, then to another, and ultimately, possibly, uniting the basins of streams whose waters were at one time quite remote from each other. With this union or coalescence of the waters there will necessarily also be a union of the contained molluscan faunas, and, by a repetition of the process, a general transferrence may in course of time be effected of the same or but barely modified forms over the most distant portions of the earth’s surface. Ex- istence, under the new conditions of habitation, will be rendered possible or materially facilitated by the comparatively slight al- teration in its physical properties to which the watery medium will in many or most cases be subjected. IV. Zoological regions.—Holarctic realm.—Neotropical.—Ethiopian.—Oriental.— Australian.— Polynesian.— Tyrrhenian, Sonoran, and Austro - Malaysian transition regions. ZOOLOGICAL REGIONS. As an outcome of the laws governing distribution, and the varying adaptabilities of animal organisms to overcoming the many conditions of existence which present themselves on the surface of the earth, it has resulted that different assemblages or groups of animals have been thrown into different quarters of the habitable globe, which may, accordingly, be said to be divided into a num- ber of regions, of greater or less extent, each of which is character- ised by its own particular fauna. To the more comprehensive of such zoological divisions the term ‘‘region” or ‘‘realm” has been applied by scientists. But just as the earth’s surface taken collec- tively may be divided into zoological regions, so may these be again further subdivided into minor regions, these still further, and so on, until we have, as generally recognised, ‘‘regions,” ‘‘sub- regions,” “ provinces,” and ‘‘sub-provinces.” By most naturalists the terrestrial portion of the earth’s sur- face is recognised as consisting of six primary zoological regions, which correspond in considerable part with the continental masses of geographers. These six regions are: 1. The Palearctic, which comprises Europe, temperate Asia (with Japan), and Africa north of the Atlas Mountains; also, the numerous oceanic islands, with Iceland, of the North Atlantic. 2. The Ethiopian, embracing all of Africa south of the Atlas Mountains, the southern portion of the Arabian Peninsula, Madagascar, and the Mascarene Islands, and which, consequently, nearly coincides in its entirety with the Africa of geographers. 3. The Indian or Oriental, which embraces 56 GEOGRAPHICAL DISTRIBUTION. India south of the Himalaya, Farther India, Southern China, Suma- tra, Java, Bali, Borneo, and the Philippines. 4. Australian, com- prising the continent of Australia, with Papua or New Guinea, Celebes, Lombok, and the numerous oceanic islands of the Pacific. 5. The Nearctic, which embraces Greenland, and the greater por- tion of the continent of North America (excluding Mexico); and, 6. The Neotropical, corresponding to the continent of South Amer- ica, with Central America, the West Indies, and the greater por- tion of Mexico. A seventh region has been established by some authors to receive New Zealand; but there would seem not to be sufficient reasons for isolating this island, or group of islands, from the Australian region. While the regions here designated are to a great extent clearly defined by their zoological characters, it would, nevertheless, ap- pear more in consonance with actual facts to depart somewhat from their generally recognised limitations. Thus, the Palearctic and Nearctic tracts, in the absence of both positive and negative faunal characters of sufficient importance to separate them from each other, are indisputably linked together, and should constitute but a single region (the Holarctic). On the other hand, the scat- tered island groups of the Pacific, which have been united with the Australian realm, may with sufficient reason be constituted into an independent region of their own; at any rate, they appear to bear no special relationship with the Australian region, any more than with the Oriental. Again, it seems advisable to separate from what has hitherto been known as the Palearctic region the tract that is comprised within the ‘‘ Mediterranean sub-region ”—i. ¢., the pen- insular portion of Southern Europe, North Africa, and, in Asia, Asia Minor, Persia, Afghanistan, Beloochistan, and the northern half of Arabia—and to consider it by reason of its faunal association as a ‘“connecting ” or intermediate region between the Holarctic, Ethio- pian, and Oriental. A similar, although not yet clearly defined, intermediate region, comprising in a general way Lower California, the province of Sonora in. Mexico, Arizona, New Mexico, and parts of Texas, Nevada, and California, with probably also the extremity of the peninsula of Florida, connects the western division of the Holarctic realm with the Neotropical; and in the Eastern Hemi- sphere, the Austro-Malaysian islands lying to the east of Bali and Borneo, as far as, and inclusive of, the Solomon Islands, form a ZOOLOGICAL REGIONS.—HOLARCTIC REALM. 57 transitionary tract between the Oriental, the Australian, and Poly- nesian realms. The major faunal divisions of the globe are, therefore: 1. The Holarctic realm. . Neotropical realm. . Ethiopian realm. . Oriental realm. . Australian realm. . Polynesian realm. a. Tyrrhenian, or Mediterranean transition region. b. Sonoran, or American transition region. e. Papuan, or Austro-Malaysian transition region. o> OF Rm oO 0 THE HOLARCTIC REALM. This division comprises the greater portion of the continent of North America, the whole of Europe north of the Alpine chain of mountains, and by far the larger half of the continent of Asia. It is preeminently the region of the Temperate and Frigid zones, and is, in fact, the only one into the consideration of whose organic products a well-marked Arctic element enters. As here defined, it comprises both the Palearctic and Nearctic regions of zoogeogra- phers, which do not differ very essentially from each other in the general characters of their faunas, or, at any rate, not nearly to the extent that the other regions differ from each other, or these in- dividually from any third. The southern limits of this Holarctic tract, owing to the intermingling along the several border-lines of its fauna with the faunas of the various other regions, is difficult of precise determination; and there can be no doubt that what at many points is considered to belong properly to one region belongs just as properly to another. But such ‘‘debatable grounds” be- tween two regions will occur in the case of any other two regions, and likewise in the case of the minor divisions—sub-regions, prov- inces, etc. In the Western Hemisphere the debatable lands between the Holarctic and the Neotropical realms cover a considerable por- tion of the Southwestern United States—namely, Arizona, New Mexico, and parts of Texas, Nevada, and California, a tract of ter- ritory generally included in the Nearctic region of most zooge- ographers. But there can be no question that the preponderating faunal element in this tract is that of the region farther to the 58 GEOGRAPHICAL DISTRIBUTION. south, the Neotropical; and the same can probably be said of the extremity of the peninsula of Florida. With these limitations the Holarctic in the Western Hemisphere embraces the whole of the United States, and all the region stretching thence northward towards and into the Arctic Sea. In the Eastern Hemisphere the southern boundary may in a general way be said to be the moun- tain complex which, as the Pyrenees, Alps, Balkans, and Caucasus, traverses the south of Europe from the Bay of Biscay to the Cas- pian, the northern line of Persia and Afghanistan, the Hima- laya Mountains, and the Nanling range in China, which forms the southern water-shed to the Yangtse-Kiang. These various boun- daries are principally of a physical nature, and of such a char- acter as to be insurmountable to most animals. No other region can compare with the Holarctic in the mani- fold variety of its physical characteristics. Every form of terres- trial configuration, or condition of soil or climate, that may be rep- resented in any other region, is also represented here, and on an imposing scale. From the ice-bound fields of the far north to the burning desert wastes of Turkestan on the south, and from the deep forest-grown lowlands to mountain summits soaring thou- sands of feet above the level of perpetual snow, we pass through all those various gradations of climate which respectively charac- terise the Frigid, Temperate, and Torrid zones. Densely covered forest tracts, supporting, as in the north, a sombre growth of pine and other coniferous trees, or, as in the south, a vegetation of almost tropical luxuriance, alternate with broadly open grass or pasture lands (tundras of Siberia, American prairies and plains), which in some cases support over enormous areas only a very scanty vegetation, and in others display a profuse variety of vegetable productions. It is in this region that, in addition to a most boun- tiful development of desert tracts, we meet with the most elevated table-land (the Central-Asian), and, at the same time, with the greatest expanse of lowland on the surface of the globe, the great plain of Siberia and Northeastern Europe. For convenience of treatment, and to facilitate comparison with other zoogeographical publications, the Old and New World divi- sions of the Holarctic region will be considered separately. The Old World or Eurasiatic Division (Palxarctic region [in part] of most authors).—The southern boundaries of this region MAMMALS OF EURASIA. 59 have already been indicated. In the northwest and west it em- braces Spitzbergen and Iceland, and the numerous larger and smaller islands which lie between these and the mainland. Although this division has an east and west extent not far short of half the circumference of the globe, yet so great is its zoological unity ‘‘that the majority of the genera of animals in countries so far removed as Great Britain and Northern Japan are identical. Throughout its northern half the animal productions of the Palex- arctic region are very uniform, except that the vast elevated desert regions of Central Asia possess some characteristic forms; but in its southern portion we find a warm district at each extremity with somewhat contrasted features.” *° Zoology of the Eurasiatic Region.—Although the Eurasiatic fauna comprises representatives of thirty distinct families of Mam- malia, not a single one of these is absolutely confined, or is pecu- liar, to that region. Perhaps on the whole its most distinctive group of quadrupeds is that of the sheep and goats, forming the sub-family Caprine of the Bovide (oxen). There are represented in this group some twenty-two or twenty-three species (belonging to the genera Capra and Ovibos), which, with four or five excep- tions, are either absolutely confined within the limits of the re- gion, or just pass beyond it. The genus Capra, comprising the goats and ibexes on one side, and the sheep on the other, have an outlying Old World representative—a goat—in the ‘‘ Warrya- to” (Capra hylocrius) of the Neilgherries (Oriental realm), and an- other—a sheep, the moufflon (C. [Ovis] musimon)—in the larger islands (Corsica, Sardinia, Crete) of the Mediterranean, and the mountains of Greece and Persia. A species of ibex (C. beden) inhabits the elevated districts of Egypt, Syria, and Sinai, and an- other (C. Valie), possibly only a variety of the preceding, the high- lands of Abyssinia, just within the boundaries of the Ethiopian realm. The two American representatives of the family, the Rocky Mountain big-horn (C. [Ovis] montana) and the musk-ox (Ovibos moschatus), are both absolutely confined to the Holarctic tract. One, at least, of the two generally recognised species of camel, the Bactrian or two-humped species (Camelus Bactrianus), is at the present time entirely, or almost entirely, restricted to the Eur- asiatic region, and not unlikely the dromedary (C. dromedarius) was also at one time indigenous to it, although from the long- 60 GEOGRAPHICAL DISTRIBUTION. continued subjection under which it has been held by man, whose wanderings the animal has been forced to follow, it has become almost impossible to determine the precise region constituting its true home. The extensive group of the antelopes, so highly indicative of the Ethiopian region, are but very sparingly represented, the most char- acteristic forms being the chamois (Rupicapra tragus), confined to the elevated mountain summits of Southern Europe, from the Pyr- enees to the Caucasus, and the saiga (Antelope saiga), an inhabitant of the plains of Southeastern Russia and the adjoining country of Asia. These are the only forms of antelope found in Europe; two or three species inhabit the Thibetan plateau, and several goat-like forms, of the genus Nemorhedas, range from the Eastern Himalayas into China and Japan. The deer (Cervide) are sufficiently abun- dant, and comprise among the more distinctive genera of the region the roe-deer (Capreolus) and the eastern musk (Moschus), the latter considered by many authors to constitute the type of a distinct family (Moschide), The stag (Cervus elaphus) ranges over nearly the whole of Europe, and eastward in Asia to Lake Baikal and the Lena River. The only members of the Quadru- mana, or monkeys, known to exist within the limits of the region under consideration, belong to the genera Semnopithecus and Ma- cacus, one species of the former (S. Roxellana) occurring in the elevated mountain region of Eastern Thibet, in about latitude 82°, and several of the latter likewise in Eastern Thibet, and also in China and Japan. The Barbary monkey (Macacus inuus), a North African species, which inhabits the Rock of Gibraltar, is the only European representative of the order; but its habitat is located within what has been designated the Tyrrhenian transition region. The Carnivora constitute an important feature in the Eurasiatic fauna, both by the number and variety of the individual forms represented and by their broad geographical range. But the actual number of carnivore genera specially distinctive of this fauna is very limited. The badger (Meles), is found throughout Central and Northern Europe and Asia, in Japan and China, in the latter country extending its range as far south as Hong-Kong, or within the boun- daries of the Oriental region. In brief, the most distinctive Eur- asiatic mammalian genera may be said to be the following : Talpa, the Mole.—Distributed throughout the entire region, and MAMMALS OF EURASIA. 61 passing in Northern India beyond its limits into the Oriental re- gion. Meles, the Badger.—Temperate Eurasia, Palestine, Japan, and China. Caumelus, the Camel.—At present distributed from the Sahara northeastward throughout Western and Central Asia to the shores of Lake Baikal, and the region of the Amoor. Capreolus, the Roe-deer.—An inhabitant of temperate and Southern Europe, and Western Asia, with a distinct species in North China. Moschus, the Musk-deer.—Central Asia, from the Amoor and the district of Peking to the Himalayas and the elevated peaks of Siam. Poephaga, the Yak.—The elevated plains of Western Thibet. Rupicapra, the Chamois.—Elevated mountain slopes of the Pyr- enees, Alps, Carpathians, Balkans, Caucasus. Saiga.—The Steppes of Southeastern Russia, and Western Asia. Capra, the Sheep and Gtoats.—The former are found in a natural state only in the mountain wilds of Corsica, Sardinia, and Crete, and in Greece, Asia Minor, Persia, and Central and Northeast Asia. The single American form, the big-horn, as above mentioned, is a native of the Rocky Mountains. The goats are found throughout nearly the whole of the South European Alpine region, from Spain to the Caucasus, whence they extend their range through Armenia and Persia to the Himalayas and China. Myoxus, the Dormouse.—Found throughout the greater part of the region. Lagomys, the Pika, or Tailless Hare.—A group of small rodents, whose distribution extends from the elevated slopes (11,000 to 14,000 feet) of the Central-Asian mountain system, and Southeastern Rus- sia, north and northeastward to the Polar Sea, and the farthest extremity of Siberia. The genus has a solitary representative in North America. Myogale, the Water-mole, or Desman.—A singular insectivorous animal, resembling the water-rat, of which there are but two spe- cies, one of them inhabiting the valleys along the northern face of. the Pyrenees, and the other the river banks of Southern Russia. Of other well-known types which may be said to be character- istic of, but which are not absolutely confined to, the Eurasiatic region, are the reindeer (Rangifer), the elk (Alces), aurochs or European bison (Bison)—now in a wild state confined to Lithuania 62 GEOGRAPHICAL DISTRIBUTION. and the Caucasus—the polar bear (Thalassarctos), and the beaver (Castor), all of which, comprising in each case but a single species, appear to be, with the possible exception of the bison, specifically” identical with North American forms. North American, or Nearctic Division.—The dominant feat- ures of the North American mammalian fauna are preeminently those which also stamp the character of the Eurasiatic fauna. Thus, among the commoner animals we have the deer, moose or elk, reindeer, bison (possibly identical with, or at least very closely allied to, the European aurochs), cats, lynxes, weasels, bears, wolves, foxes, the beaver, hares, squirrels, and marmots. Many of the forms embraced in these types, moreover, are, as has already been stated, specifically identical with their Eurasiatic congeners. But, while there are such striking resemblances between the two faunas—re- semblances that penetrate to almost all parts of the regions that are under consideration—it cannot be denied that there are also a num- ber of almost equally well-marked differences; but these are neither sufficiently numerous, nor sufficiently important, to invalidate the claims carried by the positive characters for uniting the two trans- Atlantic divisions into one region, the Holarctic. The prepon- derating element in the North American mammalian fauna (as, indeed, also in the Eurasiatic) is furnished by the group of the rodents, which here comprise nearly, or fully, one-half of all the recognised mammalian forms. Of about twenty-six genera repre- sented, nearly one-half are restricted, or are peculiar, to this re- gion; but the actual number of specific forms embraced in these peculiar genera scarcely numbers one-fourth of the total number of species. The most distinctively North American families are the Haploodontide, a very limited group (two species) of beaver- like animals inhabiting the west coast, and the Saccomyide, or pouched-rats and gophers (Saccomys, Geomys, Thomomys, &c.), animals characteristic of the fauna of the Western plains and ele- vated mountain regions. Among the rats and mice (Muride) we meet with, in addition to certain peculiar North American forms, the genus Arvicola, the field-mouse, or vole, which has an extensive representation throughout the temperate portions of the Eastern Hemisphere as well; along with this animal we find the lemming (Myodes), another Eurasiatic form. It is a singular fact, to be noted in this connection, that the typical genus Mus, which in- MAMMALS OF NORTH AMERICA. 63 cludes the common or domestic rats and mice, and which is rep- resented on all the grand divisions of the Eastern Hemisphere, is completely wanting, not only in North America, but in the entire New World, where its place is taken by the closely-allied vesper- mice, constituting the genus Hesperomys. The musk-rat (Fiber), belonging to the same family, is not found outside the limits of the North American continent, although its range extends into the Neotropical realm (Mexico). The squirrels (Sciuride) are princi- pally Old World forms; they comprise the true squirrels (Sciurus), flat-tailed flying squirrels (Sciuropterus), ground-shrews (Tamias), marmots (Arctomys), and pouched-marmots, or spermophiles (Sper- mophilus). In addition to these forms we are presented with the curious animal known as prairie-dog (Cynomys), whose range is confined to the central continental region. Among other rodents may be mentioned the jumping-rat (Jaculus, or Zapus), allied to the eastern jerboas, and the Canadian porcupine (Erethizon), be- longing to a group of animals (Cercolabide) distinguished from the true or Old World porcupines both structurally and in their arboreal habits. The ungulates, or hoofed animals, have but a very feeble development in the Nearctic division of the Holarctic realm. The goats and sheep are, with two exceptions, the big-horn (Ovis montana), an inhabitant of the Rocky Mountains, and the musk-ox (Ovibos moschatus), from the Arctic district, completely wanting, a faunal characteristic which eminently serves to distinguish the western division of the Holarctic tract from the eastern, to which almost the whole of this group of animals is confined. The ante- lopes are limited to two species, representing two distinct types, both of them confined to the more temperate regions of the conti- nent. The one is the ‘‘prong-horn” of the Western plains (Anti- locapra), and the other the Rocky Mountain goat (Aplocerus lani- ger), which, as the name indicates, is partial to the mountain fastnesses. Two varieties of the bison, or American buffalo, are recognised—the buffalo of the plains, and the buffalo of the for- ests and mountains; but the variation observable between these is one pertaining to habit and not to structure, and therefore not of specific importance. The Carnivora present several distinctively American types, and notably so the raccoons (Procyonide), a small group of interesting quedrupeds, whose home is primarily the region of the tropics, and which appear to hold a somewhat inter- 64 GEOGRAPHICAL DISTRIBUTION. mediate position between the weasels and bears. To the same family belong the South American coatis (Nasua) and the prehen- sile tailed kinkajou (Cercoleptes). The Mustelide, or weasels, com- prise the weasels proper, marten, ermine, mink, glutton, American padger (Taxidea), skunk, American otter (Latax), and the singular sea-otter (Enhydris), from the California coast. The most formi- dable carnivores are the grizzly bear (Ursus horribilis), not im- probably identical with the European brown-bear (U. arctos), and the couguar, or American panther (Felis concolor), whose range extends from the sixtieth parallel of north latitude to the southern extremity of Patagonia. One species of implacental mammal—the Virginian opossum (Didelphis Virginianus)—penetrates as far north as the Canadian frontier. Taking the Nearctic and Palearctic divisions of the Holarctic region collectively—. e., the region as a whole—we find it to be characterised by the exclusive, or almost exclusive, possession of the following families: Talpide (moles), Trichechide (walruses), Castoride (beavers), and Lagomyde (pikas); and if the reindeer, moose, and sheep and goats, be considered as distinct families, as is maintained by many naturalists, then also by the Rangiferide, Alcidz, and Capride. In addition to these seven families, we have also the hares (Leporide) and bears (Urside), which, though not exclusively restricted to these regions, are by their numbers and vast distribution, eminently characteristic of them. Of about . one hundred and twenty genera represented, upwards of seventy (or sixty per cent.) are found in no other region. Among the most characteristic forms are— In the Old World : Talpa, the mole. Rupicapra, the chamois. Meles, the badger. Saiga, the saiga antelope. Camelus, the camel. Capra, the goat. Capreolus, the roe-deer. Myoxus, the dormouse. Moschus, the musk-deer. Myogale, the water-mole. Poephaga, the yak. In the New World: Saccomys, [ea or Ovibos, the musk-ox. Geomys, gophers. Antilocapra, the prong-horn. FAUNA OF THE HOLARCTIC REALM. 65 pouched-rats or Aplocerus, the Rocky Mountain Thomomys, \ gophers. Dipodomys, goat. Perognathus, } Procyon, the raccoon. Jaculus, the jumping-mouse. Mephitis, the skunk. Fiber, the musk-rat. Latax, the American otter. Cynomys, the prairie-dog. Erethizon, the Canadian porcu- pine. Common to both divisions: Lagomys, the pika. Bison, the bison. Arctomys, the marmot. Rangifer, the reindeer. Spermophilus, the pouched-mar- Alces, the elk. mot. Thalassarctos, the polar bear. Castor, the beaver. Gulo, the glutton. Myodes, the lemming. Lyncus, the lynx, and most of the Arvicola, the field-mouse. seals and the walruses. Ovis, the sheep. The bird-faunas of the Old and New World divisions of the Holarctic tract differ very materially from each other, a condi- tion in great measure explained by the circumstance that in both a large representation is obtained through migration from extra- limital regions. Thus, the Eurasiatic or Palearctic avifauna is largely made up of types which are equally Ethiopian or Oriental; and in like manner a very large proportion of the similar North American fauna is made up of forms which might with equal justice be considered Neotropical or Nearctic. But even in the case of the resident birds, or such as may be considered to be more properly belonging to the region, marked differences, sufficient to characterise the two divisions, present themselves. The prepon- derating Eurasiatic forms belong, among the perchers, to the families of thrushes (Turdide)—with the cosmopolitan genus Tur- dus; warblers (Sylviade), with the true warblers (Sylvia), red- start, robin, and nightingale (Luscinia); nuthatches (Sittide), tits (Paride), Muscicapide (Old World fly-catchers), shrikes (Laniide), crows (Corvide), with the pies, crows proper, and jays; swallows (Hirundinide), finches (Fringillide)—gold-finch, haw-finch, cross- bill, bull-finch, linnet, sparrow, grosbeak, lark-bunting, true finch 6 66 GEOGRAPHICAL DISTRIBUTION. (Fringilla), and bunting (Emberiza), the last two almost exclusively confined to this region (and the adjoining debatable tracts)—starlings (Sturnide), larks (Alaudide), wag-tails (Motacillide), wood-peckers (Picide), king-fishers (Alcedinide), swifts (Cypselide), and pigeons (Columbidz). All of these families, not a single one of which is restricted to the Holarctic region, are, with the exception of the starlings (Sturnide) and the fly-catchers (Muscicapide), likewise distributed throughout the Nearctic division, of whose avifauna they constitute a very important factor. In the New World the true starlings are replaced by the family of hang-nests (Icteride), to which the Baltimore bird (Icterus), bobolink (Dolichonyx), cow- bird (Molothrus), and red-wing (Agelaius) belong. The Old World fly-catchers have their representatives in the tyrant shrikes (Tyran- nid), familiarly also known as fly-catchers. The true warblers (Sylviadz) are but very feebly developed in the Nearctic division, where, of about ten species, three are kinglets (Regulus), and three blue-birds (Sialia); but their place is taken by a multitude of forms belonging to the preeminently South American family of wood- warblers (Mniotiltide). Of the Holarctic gallinaceous birds the most distinctive forms in the eastern division are the true partridge (Perdix), snow-partridge (Tetraogallus), capercaillie (Tetrao), true pheasant (Phasianus), golden-pheasant (Thaumalia), tragopan (Ce- riornis), and impeyan (Lophophorus), forms either exclusively re- stricted to the region, or just passing beyond the boundaries; of the western division, the California quail (Oreortyx), cupido (Cu- pidonia), tree-grouse (Canace), sage-grouse (Centrocercus), and tur- key (Meleagris). The ruffled-grouse (Bonasa) and ptarmigan (Lago- pus) are common to the northern regions of both hemispheres. The birds of prey comprise, throughout both divisions of the region, a variety of eagles, falcons, hawks, buzzards, kites, and owls, and of forms nearly all of which are also found in other portions of the earth’s surface. America has no representative of the Old World group of (true) vultures, forming the sub-family Vulturine, their place being filled by the carrion vultures, or so-called turkey-buz- zards (Cathartine). Of the wading-birds the Eurasiatic region alone possesses the true bustard (Otis), the typical representative of a family whose members are spread throughout Africa, Asia, and Australia. The Holarctic region is deficient in reptilian forms as compared EUROPEAN REPTILE-FAUNA. 67 with the warmer regions of the earth’s surface, which appear to be more suitable to the habits of this class of animals. In the whole of Europe north of the Alps, or in what has been recognised as the ‘‘ European province,” naturalists recognise only about fifteen species of snakes, and a nearly equal number of lizards ; in the Nearctic division, while the number of lizards is not very much greater—about twenty species—that of serpents is very materially increased—to about eighty to ninety species—most of them belong- ing to the family of colubers, which includes the black constrictors. The headquarters of the rattlesnakes are situated in the debatable land bordering the Neotropical realm. The entire reptile-fauna of Europe is, according to Schreiber (‘‘ Herpetologia Europa,” 1875), comprised in sixty-two species, of which twenty-five are serpents, thirty-two saurians, and five che- lonians. Northern Europe, or the region lying to the north of the fifty-fifth parallel of latitude, is represented by but six species: Viperus (Pelias) berus, Tropidonotus natrix, Coronella Austriaca, Anguis fragilis, Lacerta vivipara, and L. agilis; the chelonians are completely wanting in this tract. Central Europe, including the Alpine system of mountains, has twenty-nine species, while the en- tire number is represented in the Mediterranean fauna. A number of additional species has been added to the list enumerated by Schreiber; but these do not materially affect the ratio for the dif- ferent zones. The most northerly of all serpents appears to be the common European viper, Viperus (Pelias) berus, whose range in Scandinavia extends to about the sixty-seventh parallel of latitude. The species is distributed throughout nearly the whole of Europe, and eastward through Central Asia to the Japanese islands; it is also found in England and Scotland, and in some of the Scotch islands (Arran, Hebrides). Tropidonotus natrix (Natrix vulgaris), a species of equally broad distribution, which is stated to ascend mountains to a height of six thousand feet, is found in Norway as far north as the sixty-fifth parallel. The most northerly, and at the same time most broadly distrib- uted, species of European lizard is the Lacerta vivipara, whose range in Norway is extended by Collett to the seventieth parallel of lati- tude. It is found throughout most of Europe (wanting in the Ibe- rian Peninsula, Southern Italy, and Greece), and is an inhabitant of the Alpine region, up to an elevation of nine thousand feet. 68 GEOGRAPHICAL DISTRIBUTION. While the Holarctic region ‘is relatively meagre in its reptilian fauna, it is preeminently the home of the tailed amphibians, newts, salamanders, &c., of which we have the blind proteus (Proteus anguinus), in the cavern-waters of Carinthia, Carniola, and Istria; the giant salamander, known as Sieboldia (Cryptobranchus), in Japan, and its allied American form, the menopoma, the eel-like sirens, mud-puppies (Necturus), and almost limbless amphiumes of the Eastern and Southern United States; the true salamander and triton in Europe and Asia, and their American representatives, the amblystomes, to which the singular form known as the axolotl be- longs. The European tail-less amphibians (frogs and toads) number some dozen or more species of the genera Bombinator, Pelobates, Alytes, Hyla, Discoglossus, Rana, and Bufo, the most broadly dis- tributed of which appears to be Rana temporaria and R. esculenta, the former extending its range eastward to Japan and America, and northward in Norway to beyond the seventieth parallel of latitude. The fish-fauna of the Holarctic tract is characterised by the spe- cial development, among fresh-water forms, of the carps (Cypri- nid), salmon (Salmonide), pikes (Esocide), perches (Percide), sculpins or bull-heads (Cottide), sticklebacks (Gasterosteide), stur- geons (Accipenseride), and lampreys (Petromyzon), which are dis- tributed over both the eastern and western divisions of the region. The Cyprinoids are especially abundant, constituting, in the number of species, according to Ginther (Ency. Brit., XII., p. 675), nearly two-thirds (two hundred and fifteen species) of the entire fish-fauna of temperate Europe (including the Mediterranean transition region) and Asia, and more than one-third (one hundred and thirty-five species) of the equivalent fauna of North America. The cat-fishes (Siluride), so eminently characteristic of the more southerly equa- torial zone, are largely deficient in the number of species. Silurus occurs in some of the Eurasiatic waters as an immigrant from India; most of the North American forms belong to the genus Amiurus. Among the more distinctive ichthyic features separating the faunas of the eastern and western divisions of the Holarctic realm are the possession, by the former, of the barbels (Barbus) and cobitoids, and, by the latter, of the suckers (Catostomide), sun-fishes (Cen- trarchide, most abundant in the Mississippi Valley), and two genera of ganoid fishes, Amia and Lepidosteus, both of which occur as fossils in the Tertiary deposits of North America, and the latter HOLARCTIC SUB-REGIONS. 69 also in Europe. On the other hand, the two regions éxhibit a marked inter-relationship by the possession of a number of identical specific forms, as Accipenser sturio (sturgeon), Perca fluviatilis (perch), Salmo salar (salmon), Esox lucius (pike), Lota vulgaris (ing), &e. The correspondence existing between the vertebrate faunas of the Old and the New World divisions of the Holarctic tract extends also to the Invertebrata, and is especially marked in the case of the beetles (Staphylinide, Carabide), butterflies, and the land and fresh-water mollusks (Limneea, Planorbis, Physa, Paludina, Val- vata). The land-snails (Helicide) and naiades (Unionide) are very largely developed, the latter more particularly in the American Streams, where distinctive types appear to be relegated to the dif- ferent water-courses. The eastern melanians are wholly wanting in America, where they are replaced (principally to the east of the Mississippi River) by the members of the allied family of the Stre- pomatide (Io, Goniobasis, &c.). The Holarctic realm may be conveniently divided into the fol- lowing sub-regions: 1. The Boreal Sub-Region, which extends northward into the Polar Sea, and whose southern confines are fixed approximately by the northern limits of the cultivation of the cereals, and the southern limits of the migration of the reindeer. In the Western Hemisphere it comprises most of the region lying to the north of the United States and Canada boundary-line, and in Eurasia the tract lying north of a line starting from about the sixty-sixth parallel of latitude, on the Norwegian coast, and passing southeastward to the East Asiat- ic coast, in about latitude fifty degrees north. The fauna of this region is a very homogeneous one, and, generally speaking, also a limited one. Among the more distinctive mammalian forms, which comprise almost exclusively only ruminants, carnivores, and rodents, are the Arctic fox (Canis lagopus), polar-bear, glutton, ermine, mink, sable, walrus, variable hare, lemming, and reindeer. The musk-ox, which occurs fossil in the Quaternary deposits of Europe, is at the present time found only in America. Among the more character- istic birds are the snow-partridges (Lagopus), snowy-owl (Surnia nivea), Iceland falcon (Falco candicans), eider-duck (Somateria mol- lissima), and various alks (Alca), divers (Colymbus), and guillemots (Uria, Lomvia). Captain Markham observed the footprints of the 70 GEOGRAPHICAL DISTRIBUTION. polar-hare in the snow-bound ice in latitude 83° 10’, and the antlers of a reindeer were picked up by the officers under Sir George Nares, in latitude 82° 45’ (Grinnell Land). A skeleton of the latter ani- mal, recently picked by wolves, was also obtained in latitude 80° 27’. Traces of the rock-ptarmigan (Lagopus rupestris) have been met with as far north as latitude 83° 6’, and the snow-bunting (Plec- trophanes nivalis) in latitude 82° 33’. .The reptile-fauna is very limited, no serpent, apparently, passing beyond the sixty-seventh ‘parallel of latitude, and no lizard above the seventieth. The fishes, which include the common perch and pike, are mainly Salmonoids. Insects are fairly numerous, and even in the far north the number of species is considerable. Sir George Nares obtained no less than forty-five species, representing nearly all the orders Qncluding Lepi- doptera) in Grinnell Land; Greenland has thus far yielded eighty species, and Iceland three hundred. Among the most northerly genera of non-marine mollusks are Helix, Pupa, Succinea, Limnea, and Planorbis. 2. The Huropean Sub-Region, which includes practically the whole of Europe lying between the Arctic tract and the Alpine system of mountains, extending southeastward and eastward to the Caucasus and the Caspian steppes. The fauna of this region is typically that of temperate Eurasia, taken as a whole, and therefore requires no elaborate analysis. Among its more or less characteristic Mam- malia are the moose or elk (in the north), stag, roe, aurochs (Bison Europzus, in the Caucasus and the forests of Lithuania), the Alpine chamois and ibex (with the accompanying marmot, Arctomys mar- motta), brown bear (Ursus arctos), badger, glutton, dormouse, hamster (Cricetus frumentarius), mole (Talpa Europea), and hedge- hog (Erinaceus Europeus), many of which also form integral parts of the Arctic and Central Asian faunas. The birds comprise sev- eral hundred species, of which Germany alone possesses nearly three hundred; distinctive types are, however, not numerous—indeed, they may be said to be almost wholly wanting—and even the num- ber of restricted forms is very limited. Among these may be men- tioned a number of song-birds of the finch tribe, as the chaffinch (Fringilla ccelebs), siskin (F. spinus), goldfinch (F. carduelis), bull- finch (Pyrrhula rubricilla), yellow-hammer (Emberiza citrinella), and linnet (Linoia linaria), and the nightingale (Luscinia). ~The most distinctive bird of prey is the bearded vulture of the Alps, or FAUNA OF CENTRAL ASIA. val lammergeier (Gypaétus barbatus). The reptilian-fauna, as has already been remarked, when treating of the Eurasiatic region’ generally, is very limited. Among the poisonous serpents are the Pelias berus and the sand-viper (Vipera ammodytes), the range of the latter extending from the Mediterranean into Sweden. 8. The Central Asian Sub-Region, comprises that portion of the Holarctic tract which lies south of the Arctic sub-region, and is included between the European sub-region on the west and China proper and Manchuria on the east. A steppe character prevails in the western portion of this region, to which desert features are also added, and hence we find a distinct individuality imparted to its fauna. The rodents, whose most distinctive forms are the spermophiles and jumping-mice (Dipus, Scirtetes), are more ex- tensively developed than in the European tract; on the other hand, the larger Carnivora are almost completely wanting, although the tiger seems to occasionally reach the region about the Caspian and Aral seas. The deer are replaced by one or more forms of ante- lope (Saiga), which, with the exception of the camel and some wild equine representatives, are almost the sole hoofed animals of the region. A distinctive faunal feature is constituted by the seals of the Caspian (Phoca Caspica), which appear to be very closely related to the common Phoca vitulina of the North Atlantic. Among the birds may be mentioned the steppe partridges (Pterocles, Syr- rhaptes), and, as an occasional visitor, not improbably also the ostrich. Reptiles are fairly abundant, and include among the lizards the agamid genus Stellio, and among serpents the sand- snake (Psammophis) and the poisonous Trigonocephalus. In the eastern half of the Central Asian sub-region, plateau and desert features largely predominate, and the fauna acquires some- what distinctive characters. The ungulate and carnivore types of Mammalia are more abundantly represented, the former comprising, in addition to the camel (Camelus Bactrianus), whose range ex- tends to the shores of Lake Baikal, and two or more species of antelope, the dziggetai or kiang (Equus hemionus) of the plains of Thibet, the recently-discovered species of wild horse described by M. Poliakoff as Equus Przevalskii, the Thibetan yak, several wild goats, and the argali (Ovis argali), the last recalling the big-horn of the Rocky Mountains. The tiger and ounce (Felis uncia) both range across the region into Siberia, sharing the habitat of the 72 GEOGRAPHICAL DISTRIBUTION. snow-leopard (Felis irbis). The grouse, partridges, steppe part- Tidges, and bustards constitute important elements in the bird- fauna, which exhibits the general features of the north temperate region. 4. The Manchurian Sub-Region embraces Manchuria, Northern China (with a westerly extension along the northern face of the Himalayas), and the Japanese islands. The fauna, especially in the more southern districts, exhibits characters drawn from both the Tropical and Temperate zones. A distinguishing feature of this sub-region is the presence of monkeys, which are represented by the genera Macacus and Semnopithecus, the former penetrating even into Japan. The Cervide, whose range extends into Japan (where the antelope is also met with), are represented by both horned (Elaphodus) and hornless species (Hydropotes, Lophotra- gus), and by the diminutive musk-deer (Moschus moschiferus), which inhabits the mountain-valleys from the Amur to the Hima- layas. The edentates have their most northerly representative in the scaly Manis (Japan). Among the more distinctive carnivore forms are the genera Lutronectes, Ailuropus, and Nyctereutes. The facies of the Japanese bird-fauna is distinctly European, but in China, which is properly the home of the pheasants, there is a considerable intermixture of tropical (Oriental, &c.) forms, such as the babbling-thrushes, caterpillar-eaters, honey-suckers, and weaver- finches. 5. The Alleghanian Sub- Region may be approximately defined as comprising that portion of the Holarctic realm in the Western Hemisphere which lies south of the Arctic tract and east of the one hundredth meridian of west longitude (Greenwich). Its faunal features are those of the North American or Nearctic division gen- erally, although among the Mammalia a deficiency is brought about by the absence of some of the pouched-rats or gophers, the big- horn (Ovis montana), the Rocky Mountain goat (Aplocerus lani- ger), and the musk-ox, which, with the exception of the last, belong to, or are most abundant cn the central or Rocky Mountain sub- region. The majority of the Arctic Carnivora penetrate to within, or far beyond, the northern boundary-line, and the same is true, to « certain extent, of the moose and caribou (reindeer). The more strictly southern forms are the opossum, raccoon, and pec- tary, the last, however, not penetrating farther north than the NEOTROPICAL REALM. 3 Red River, in Arkansas. The bison, which was at one time very abundant on the western prairies, has now almost wholly disap- peared, and impending destruction likewise threatens the prong- horn (Antilocapra Americana), which in the furcation and shedding of its horns may be considered to be the most divergent type of all antelopes. Characteristic rodent forms of the prairies are the prairie- dog (Cynomys Ludovicianus) and the gopher (Geomys bursarius). More properly belonging to the eastern wooded sections are the beaver (in the north), identical with the European species, the skunk, and Canada porcupine. 6. The Rocky Mountain Sub-Region comprises the mountainous tracts of the West-Central United States, and a similar region in Canada extending to about the fifty-fifth parallel of latitude. Its southern boundary is determined by the as yet not very exactly defined Sonoran transition region. Its general and distinctive faunal features have already been indicated. %. The Californian Sub-Region is comprised within the border- land which stretches along the Pacific west of the main mountain axis, and extends northward to about the fiftieth parallel of latitude. Many of its faunal features are borrowed from the Neotropical realm, but in its entirety the fauna is distinctively North American. Among its characteristic mammalian forms are the sewellel (Ha- ploodon) and the grizzly bear (Ursus horribilis). Other distinctive types are the California condor (Sarcorhamphus Californianus), the ground cuckoos (Geococcyx), and the singular bird known as Chamea. The number of humming-birds is greater than in the Eastern United States. THE NEOTROPICAL REALM. This region, as usually recognised, comprises the continent of South America, the West India Islands, Central America, and the lowlands—tierras calientes—on either side of the Mexican plateau. While, therefore, it is in the main clearly circumscribed by its water-boundary, the northern portion, or that which borders on the Holarctic, is much less sharply defined, as must invariably be the case where two faunal regions overlap. The principal features of the greater portion of this vast tract are singularly uniform. An enormous expanse of forest, unequalled for its continuity and luxu- riance of growth, occupies fully one-half of the surface area, cover- 4. GEOGRAPHICAL DISTRIBUTION. ing not only the deep lowlands, but also the mountain-slopes to a very considerable elevation. Commencing on the Atlantic border, it stretches, through a north and south extent of thirty degrees of latitude, almost unbroken for nearly three thousand miles to the base of the Andes, harbouring in its dense recesses a host of the most varied animal forms. Beyond, and partially enclosed within, the limits of this vast forest region are the various forms of pasture- land, or grassy plains, the llanos or savannas of Venezuela, the campos of the highlands of Brazil, and the pampas of the Argen- tine Republic and Patagonia. In the great Andean chain, which traverses in one continuous sweep the entire north and south ex- panse of the region, we have all the more characteristic features of a mountain-system developed on a most gigantic scale—high pla- teaus, deep valleys, wooded and barren slopes—conditions affecting in a most marked degree the diversity of its animal and vegetable creations. Desert areas, or such as are rendered almost unfit for habitation by reason of extremes of climate, like the north of both the North American and Eurasiatic continents, are, if we except the most elevated mountain-summits, limited to a few scattered patches of small area in the Argentine Republic, and to a narrow tract of littoral lying in Peru and Chili, on the Pacific side of the mountain-axis. Zoological Characters of the Neotropical Realm.—In com- paring the fauna of the Neotropical with that of the other zoogeo- graphical regions we are struck with two things: 1, its extraordi- nary richness; and 2, the very great preponderance of forms that are peculiar to the region and not met with anywhere else. According to Wallace, the region comprises no less than forty-five families and nine hundred genera of vertebrate animals which are strictly pe- culiar to it, while it has representatives of one hundred and sixty- eight out of the total of about three hundred and thirty families recognised by naturalists ; in other words, more than one-half of all the families scattered over the globe are here represented. Of about thirty-one mammalian families eight are almost completely confined to the region, as follows: The Cebide, or true South American monkeys; the Hapalide, or marmosets; the Phyllosto- mide, or simple leaf-nosed bats, which include the vampires (with one extra-limital species in California); the Chinchillide, compris- ing the chinchilla and vizcacha, a small group of animals confined NEOTROPICAL MAMMALIA. 5 principally to the Alpine slopes of the Andean chain, in Peru, Bo- livia, and Chili, but also (Lagostomus) inhabiting the lowland plains of the Argentine Republic and Uruguay; the Caviide, the cavies (Cavia) and agouties (Dasyprocta), a family of rodents to which the guinea-pig belongs, and whose members range from Mexico to be- yond the forty-eighth parallel of south latitude; the Bradypodide, or sloths, confined exclusively to the forest region; the Dasypodide, or armadillos,-which are found throughout almost the entire region, with one species (Dasypus peba) penetrating as far north as Texas; and the Myrmecophagide, or ant-eaters. The Cebidw, or South American monkeys proper, constitute a very distinct group of quad- rumanous animals (Platyrhina), distinguished, from the monkeys of the Old World (Catarhina) by several very prominent characters, such as the broad nasal septum (whence the designation of flat- nosed monkeys, Platyrhina), the absence of ischial callosities and cheek-pouches, and the presence of an additional premolar tooth on 18 each side of each jaw, making the total dental formula a 36, in- 16 stead of _ 32, as we find it in the Old World apes and man. In the smaller group of the marmosets and lion-monkeys (Jacchus, Mi- das) we find the same number of teeth as in the catarhines, but the re- lation of the premolars to molars is reversed, i. ¢., they are arranged 3—3 2—2 2—2 according to the formula 3g P™ gg i instead of pm. at m. = . In none of the American monkeys is the thumb com- pletely opposable to the other fingers, an important distinguishing character; and scarcely less important is the presence, in most cases, of a prehensile tail, which, as such, is developed only in this group of the Quadrumana. The range of the American monkeys, in marked contrast to that of the African, is limited virtually to the forest region, in which alone they find their proper sustenance. Their most southern extension appears to be about the thirtieth parallel of south latitude, and their most northern, the southern portions of Mexico. No representatives of the order are met with in any of the West India Islands, which are also wanting in all Car- nivora and Edentata. The Platyrhina comprise, among other groups, the well-known howling-monkeys (Mycetes), spider-monkeys (Ate- %6 GEOGRAPHICAL DISTRIBUTION. les), and capuchins. The Neotropical Carnivora embrace a number of larger and minor cats, the most formidable of which are the jaguar and couguar (puma), the former ranging from the pampas of the Argentine Republic to Texas, and the latter, as has already been observed, from Patagonia to about the sixtieth parallel of north latitude in Canada. Among the lesser animals of this family are the jaguarundi, ocelot, and other so-called tiger-cats. Of the weasels, there are no representatives of the genera Mustela or Putorius over the greater part of the region. The Canide are represented by various forms of wild-dogs (Icticyon, Lycalopex, Pseudalopex), which are principally confined to the open grass-country; the wolf and fox are both absent, except from certain portions of Mexico, which ought, perhaps, more properly to be relegated to the inter- mediate tract which separates this from the Holarctic region. The only member of the Urside found in the entire continent of South America (with Central America) is the ‘‘spectacled” bear (Ursus ornatus), from the Chilian and Peruvian Andes, which, through certain peculiarities of structure, has been separated by some au- thors from the true bears (Ursus), and placed in a distinct group, Tremarctos. Among the distinctive rodents, other than the cavies and agouties, are the subungulate capybara and paca, and the beaver-like coypu (Myopotamus). A negative feature is the almost total absence of Insectivora. The hoofed animals (Ungulata) are but very sparingly represented in the Neotropical realm, a circum- stance in marked contrast to what is presented by the similarly- situated Ethiopian or African region. The antelopes, so char- acteristic of the warmer parts of both the African and Asiatic continents, are completely wanting, and there are likewise neither indigenous horses, oxen, sheep, nor goats. A comparatively lim- ited number of species of deer are scattered throughout the region, from Mexico to the Rio Negro in Patagonia. Of other even-toed ungulates (Artiodactyla) we have the peccaries (Dicotyles), the American representatives of the Old World family of swine (Suide), whose range extends to the Red River, in Arkansas, and conse- quently considerably beyond the limits of the region; and the llama, alpaca, guanaco, and vicufia, together constituting the genus Auchenia, which ace the New World representatives of the camel family (Camelide). It is a most striking fact in the distribution of this family of ruminants, that the only two genera of which it FAUNA OF THE NEOTROPICAL REALM. 4 is composed should, in their habitats, be separated by one-half of the circumference of the globe; and that, further, while the one genus, Camelus, belongs strictly to the Northern Hemisphere, the other, Auchenia, is restricted to the Southern. But these are not the only peculiarities distinguishing this singularly discontinuous family, for, while the Eastern representatives are specially adapted to an existence in the hot and parched surfaces characteristic of desert lands, those of the Western Hemisphere, on the contrary, are habituated to the rugged and snow-covered slopes of the South American Cordilleras.* The tapir, which, with the exception of the peccary, is the only pachydermatous South American mammal, presents us with an example of a discontinuous family no less marked than that of the Camelide. Its four to six members are, with one exception, all confined to South and Central America, in- habiting the lofty mountain regions of from eight to twelve thou- sand feet elevation, as well as the lowland equatorial forests. The only extra-limital representative of the family is the Tapirus Malay- anus, or white-banded Malay tapir, whose home, the Malay Penin- sula, Sumatra, and Borneo, is separated from that of its American congener by an interval of nearly one-half the earth’s equatorial circumference. The bird-fauna of the Neotropical realm is no less striking by its diversity than the mammalian. It comprises representatives of upwards of six hundred and eighty genera of land-birds, of which some five hundred and seventy, or just five-sixths of the entire num- ber, are peculiar to it.** The vernal migration naturally tends to spread many of the South American avian types northward, and thus a large number of even the more strictly Neotropical forms have what might in a measure be considered North American or Holarctic representatives. Of the humming-birds (Trochilide), a distinctively South American family, comprising about one hundred and twenty genera, and upwards of four hundred species, no less * The vicufia is rare!y found at a lower level than thirteen thousand feet ; the Ilama descends to three thousand. It has already been remarked, when treating of the influence of climate upon distribution, that, while the camel is more properly an animal of the warm country, it yet winters, with apparent comfort, as far north as the region of Lake Baikal, in latitude 52° to 58°, Again, while most suitably adapted to a desert region, the animal, it appears, can conveniently accommodate itself also to rugged mountain-slopes. %8 GEOGRAPHICAL DISTRIBUTION. than fifteen species are found within the limits of the Holarctic realm and the Sonoran transition tract, one species, the ruby-throat (Trochilus colubris),‘on the east coast of the continent of North America extending its range northward beyond the Canadian bor- der, and one (Selasphorus rufus) on the west as far north as Sitka. So, again, the Conurine, or macaws, an equally distinctive Neo- tropical group, with about eighty species, have a solitary Holarctic representative in the Carolina parakeet (Conurus Carolinensis), whose range, at the present time, seems not to extend much farther than the State of South Carolina, but which, until a comparatively recent time, penetrated as far north as Nebraska. The Cerebide, or sugar-birds, whose brilliancy of plumage rivals that of the hum- mers, have an outlying member in Certhiola Bahamensis, of which a colony has been established on one of the Florida Keys, or just beyond the limits of the Neotropical realm.?”_ Other characteristic families of South American birds are the toucans and aracaries (Rhamphastide), a strictly frugivorous group, recalling by the structure of the bill the distant Old World horn-bills; the jaca- mars (Galbulide); the saw-bills, or motmots (Prionitide); the Pipride, or manakins; the Cotingide, or chatterers, which in- clude, besides the cotingas and pompadours, the famous cock-of- the-rock (Rupicola), umbrella-bird (Cephalopterus), and bell-bird (Chasmorhynchus); the Dendrocolaptide, or tree-creepers, with upwards of two hundred species; the wonderfully variegated tana- gers (Tanagridz), with upwards of three hundred species, which may in a measure be considered to occupy the place of the Tem- perate Zone finches and sparrows, and of which the common scarlet tanager (Pyranga rubra) and summer-redbird (Pyranga sstiva) are familiar North American examples; to the same group belong the South American spice-birds of the genus Calliste, and the or- ganist (Euphonia); the Cracide, curassows and guans, which are the largest game-birds of the region, and which take the place of the Old World grouse and pheasants; and the Tinamidsa, or tina- mous, a group of birds recalling in their genéral appearance the partridges, and possessing certain affinities with the ostriches. The exquisitely decorated trogons (Trogonide) present us with one of the most remarkable instances of a discontinuous family, whose representatives are found at opposite points of the earth’s equatorial circumference—the Neotropical and Oriental regions. The inter- FAUNA OF THE NEOTROPICAL REALM. 9 vening continent of Africa appears to be almost entirely deficient in the members of this family. The Struthionide, or ostriches, are similarly divided, the South American continent possessing three (of the genus Rhea) out of the five or six species of which the family is composed. The noble and ignoble birds of prey are both well represented in the Neotropical realm, and it is here that the most powerful and largest bird of flight, the Condor (Sarcorham- phus gryphus), is to be found. ‘True eagles of the sub-family Aquilins are absent from the greater part of the region, and there are no representatives of the common genera distinctive of the Temperate Zone—Aquila, Haliaétus (the bald eagle), or Chrysaétos (the golden eagle). The harpy eagle (Thrasaétus harpya), more properly a buzzard, penetrates as far north as the Texan frontier. Among the characteristic families of birds which the Neotropical region shares with the western division of the Holarctic are the Tyrannide, or tyrant-shrikes, the New World representatives of the Old World fiy-catchers (Muscicapide), and the Icteride, or hang-nests, the New World representatives of the Old World starlings (Sturnide), of which the common Baltimore oriole and the cassique (Cassicus cristatus) are familiar examples. It is a singular fact that the crows and ravens (Corvus), which are otherwise nearly cosmopolitan, and which comprise upwards of fifty species, are completely wanting in the greater part of the Neotropical realm, no species being found south of Guate- mala, The Neotropical reptile-fauna is scarcely less well-marked than the mammalian or the avian. It includes the giant boas and ana- condas of the genera Boa, Epicrates, and Eunectes, the coral-snake (Elaps), which has one or two extra-limital representatives in the United States, the venomous crotaloids, with the true rattlesnakes, Lachesis, and Craspedocephalus (jararaca), both alligators (cayman) and crocodiles, and no less than about one hundred and fifty species of the singular lizards constituting the family Iguanide. The ano- lids and amphisbeenians are represented by numerous species. The tailed amphibians, such as the newts and salamanders, are almost absent, but in their place there is an unusual development of the tailless forms, the toads and frogs (horned-frog, Ceratophrys; Hemi- phractus), especially of the tree-frogs (Hylide).—The fresh-water fishes of the Neotrop:cal realm arc specifically more numerous than 80 GEOGRAPHICAL DISTRIBUTION. those of any other region, with perhaps the exception of the Hol- arctic. According to Gimther they comprise nearly seven hundred distinct forms, although representing only nine families. About one-third of the species belong to the family Characinide, and a somewhat larger number to the cat-fishes (Siluride). The toothed-carps (cyprinodonts) are represented by sixty or more species. Among the distinctive fishes of the region are the electric eel (Gymnotus electricus), from the equatorial regions, and the remarkable lung-fish (Lepidosiren paradoxa) of the Ama- zon. The Neotropical tract may be conveniently divided into the following sub-regions: 1, the Brazilian, comprising Brazil, Guiana, Venezuela, Colombia, Ecuador, Paraguay, and the cis-Andean por- tions of Peru and Bolivia, inclusive of the eastern slope of the mountain-axis, essentially a region of dense and luxuriant forests; 2, the Chilian, principally a region of open plains and pampas, comprising Chili, Patagonia, the Argentine Republic, Uruguay, and the remaining parts of Peru and Bolivia, extending to about the fourth parallel of south latitude; 3, the Mevican, including the Isthmus of Panama, Central America, and Southern Mexico ; and, 4, the Antillean, or the sub-region of the West India Isl- ands. In the first of these sub-regions, the. Brazilian, the faunal facies is essentially that of the Neotropical realm taken as a whole, inasmuch as there is scarcely a single group of important or typical South American animals which has not its representatives here. Furthermore, the majority of these forms have their greatest de- velopment in this tract. Among its most distinctive negative elements may be cited the chinchillas, the spectacled bear, the llamas (with the alpaca, vicufia, and guanaco), the rheas (South American ostriches), and the condor—members of the fauna of the Chilian sub-region—which are either wholly wanting, or but barely pass beyond the regional confines. Positive distinguishing characters among the Mammalia may be found in the special de- velopment of the quadrumanous and edentate types—among the former, in addition to the more widely distributed forms, such as Cebus, Ateles (spider-monkey), and Mycetes (howler), the woolly- monkeys (Lagothrix), the sakis (Pithecia), the douroucoulis or night-monkeys (Nyctipithecus), squirrel-monkeys (Chrysothrix), and some thirty or more species of marmosets, which appear to be con- FAUNA OF THE NEOTROPICAL REALM. 81 fined to the tropical forests; and among the latter, several species of armadillo, the great ant-eater (Myrmecophaga jubata), and the various forms of two-toed (Cholepus) and three-toed (Bradypus) sloths—the spiny-rats (Echimyide), most of whose representatives are confined to this region, and the manatee or vacca marina (Ma- natus), which ascends the river Amazon. Among the more re- stricted birds are the capitos, the trumpeter (Psophia), screamer (Palamedea), hoazin (Opisthocomus), pauxi, and boat-bill (Can- croma). The fauna of the Mexican or Central American sub-region corre- sponds closely with that of the sub-region just described, from which it differs mainly by the comparative paucity of its developed types, and by the more pronounced infusion of the Holarctic or northern element. As representatives of the latter we have the shrews, the hare (one species also in Brazil), ground-squirrel, fox, and Basgaris. The very limited number of distinctive types include the Central American tapir (Elasmognathus Bairdii), Myxomys among the mice, and Heteromys among the pouched-rats.—The Chilian fauna, some of whose more prominent features have already been indi- cated, is broadly distinguished from the faunas of the north by its negative characters, as well as by the few distinctive types which more ot less belong to it—llama, alpaca, vicufia, guanaco, spectacled bear (Tremarctos ornatus), Patagonian cavy (Dolichotis), coypu (Myopotamus coypu), chinchilla, viscacha (Lagostomus), Chlamy- dophorus (among the armadillos), and several peculiar genera of mice and the rat-like octodonts. The puma, deer, and skunk ex- tend their range to the Strait of Magellan, and the wolf-like dogs of the genus Pseudalopex, the guanaco, and several mice (Reithro- don, Hesperomys) into Tierra del Fuego. The monkeys, tapirs, peccaries, and sloths are wanting.—With respect to its mamma- lian-fauna the Antillean sub-region, as might be expected, pre- sents the most negative features. There are neither carnivores, monkeys, nor edentates, the only orders represented being the bats, rodents (Capromys, Hesperomys), and insectivores. -The last are represented by two species of the genus Solenodon, whose nearest allies are the Centetide of Madagascar. An agouti inhabits some of the islands of the Lesser Antilles (St. Vincent, Sta. Lucia). The resident land-birds are comprised in about one hundred genera and upwards of two hundred species, about one-third of the former and 82 GEOGRAPHICAL DISTRIBUTION. nearly nine tenths of the latter being peculiar. The remaining species are South American or Central American forms. In addi- tion to this number there are some ninety or more migrants from North America. THE ETHIOPIAN REALM. Next in importance to the Neotropical realm in the number, variety, and peculiarity of its animal productions, is the Ethio- pian, or African. This region comprises the entire continent of’ Africa south of the Tropic of Cancer, and likewise that portion of Arabia which lies to the south of the same line; the Island of Mada- gascar, with some neighbouring groups of smaller islands, is also included. By some naturalists the northern boundary is extended as far north as the Atlas Mountains, thus including the entire Desert of Sahara. With the limitation first assigned almost. the entire region lies within the tropics, and is thus the most strictly tropical of the faunal regions. In its physical features it presents several well-marked peculiarities. In the ‘first place, we have the vast expanse of desert, which in the north occupies a transverse band varying in width from about four to nearly ten degrees of latitude. This is succeeded by what may not improperly be termed the open pasture-lands, which, as a narrow belt bounds the Sahara on the south, curves southwards at about the position of Kordofan, and occupies the greater portion of the continent lying east of the thir- ticth parallel of east longitude and south of the fifth parallel of south latitude. A very considerable portion of this pasture tract forms a plateau of from four thousand to five thousand feet elevation. Included within it, and bounded on the west by the Atlantic Ocean, is the region of the great equatorial forests, to the present day a terra incognita in great part to both geographers and naturalists. That portion of the African continent lying south of the Tropic of Capricorn differs in many respects, both as to its physical con- figuration and its vegetable products, from the region to the north- ward, and is characterised by a vegetation which is at the same time one of the richest and most remarkable on the globe. With this marked peculiarity in its vegetable development there is of necessity a certain amount of faunal peculiarity superadded as well, but this is not sufficiently pronounced topermit of a separation of this tract from the tract lying immediately to the north. We have ETHIOPIAN MAMMALIA. 83 ‘thus on the continent three strictly-defined faunal sub-regions : 1, ‘the pasture-lands already described, constituting the Eust-Central «lfrican sub-region, through whose vast expanse there is manifest a strong identity in the character of the animal products, the same or very closely related animal forms being in many instances found at the extreme points of the region; 2, the forest tract, constitut- ing the West African sub-region, whose animal products naturally differ very essentially from those of the last; and, 3, the desert or Saharan sub-region, containing a comparatively limited fauna, which, with almost insensible gradations, merges into the fauna of the Mediterranean transition tract. To the same division belong in great measure the desert tracts of Arabia, or that portion of the peninsula lying to the south of the Tropic of Cancer. The Island of Madagascar, with Mauritius, the Seychelles, &c., forms an in- -dependent sub-region of its own. Zoological Characters of the Ethiopian Realm.—The mam- malian-fauna of the Ethiopian region is characterised no less by the remarkable development of its carnivore and hoofed animals (Ungulata) than by the peculiarities presented in its quadrumanous types. Of the hoofed animals there are two families which are absolutely restricted to the region: the Hippopotamide, or hip- popotami, and the Camelopardide, the giraffes. The former com- prise two species, the common hippopotamus (H. amphibius), which is found in nearly all the larger African rivers from the Cape to the Sahara, and from the Zambesi to the Senegal, and the smaller Liberian hippopotamus (Cheeropsis Liberiensis), from the river St. Paul on the west coast, characterised by the possession of only one pair of incisors instead of the normal two pairs.* The latter in- cludes but a single species, the well-known giraffe (Camelopardalis giraffa), which ranges throughout the greater portion of the African open country, and to a certain extent also invades the forest region. As to the pigs (Suid), a family very closely related to the Hippo- potami, the Ethiopian region is deficient in the genus Sus, which * In antiquity the hippopotamus appears to haye been very abundant in the waters of the Nile as far down as Lower Egypt. Even as late as 1600 hippopotami were trapped at Damietta. situated at the mouth of one of the arms of the Nile, and in the early part of this century they were still ob- served by Rappell in Nubia. At present they are found in the Nile only in its upper course. 84 GEOGRAPHICAL DISTRIBUTION. comprises the common hog or wild-boar of Eurasia, but its place is taken by the so-called ‘‘ water-hogs” and ‘‘ wart-hogs,” of the genera Potamocherus and Phacocherus. Of the Rhinocerotide, a family which this region shares with the Oriental or Indian, there are four or five species or varieties, all of them two-horned. By far the most important of all the African ungulates are the ruminants. We have here an extraordinary development of the antelopes, which in the number of their species far surpass those of all the other regions put together. No less than from eighty to ninety distinct species have already been described, and doubtless many more re- main in the districts that have not yet been explored. Among the numerous genera of these animals, which comprise forms ranging in size from the dimensions of a large ox (eland) to those of a rabbit (m’doqua, guevi), there are none that are found in any other faunal region, excepting Gazella, the gazelle, and Oryx, to which the gems- bok belongs, the former represented by a limited number of species in the desert regions of Western and Southwestern Asia (Arabia, Persia), and the latter, by a single species, also from the Arabian desert. The antelopes may be conveniently divided by their habits into four groups: 1. The desert antelopes, or such as frequent the desert regions, like the gazelle; 2. The bush antelopes, or those which habitually frequent the forest recesses, like the koodoos, water-bucks, and bushboks; 3. The rock antelopes, which, like the klipspringer, recalling in aspect and habits the European chamois, frequent the mountain-fastnesses ; and, 4. The antelopes of the open plains—gemsbok, blessbok, hartebeest, gnu, springbok — which comprise the greater number of species, and which, as the springbok, not unfrequently congregate in herds of several hundreds or even thousands. The more familiar forms of ruminants, such as the deer, sheep, and goats, are, with the exception of an ibex found in the Abyssinian highlands, completely absent. The only deer-like animal found on the African continent south of the Sahara is the chevrotain (Hyeemoschus aquaticus), from the region lying between the Senegal and the Gaboon, a small animal closely allied to the Oriental musk- deer, whose nearest representatives, the Traguli, inhabit the south- eastern extremity of the continent of Asia, and the adjacent islands of the East Indian Archipelago. The wild-ox (Bos) is also absent, but its place is occupied by the Cape buffalo (Bubalus Caffer), whose domain extends throughout the greater portion of South, Central, ETHIOPIAN MAMMALIA. 85 and Western Africa. Characteristic non-ruminating ungulates are the zebras and quaggas (Equus zebra, Burchellii, Grevyi, and quagga), and the Abyssinian wild-ass (Equus teniopus), by many naturalists supposed to be the progenitor of the domestic animal. Among the beasts of prey (Carnivora) there are the lion (possibly two species), leopard, panther, the spotted, striped, and brown hyenas, jackal, and the aard-wolf (Proteles), an animal in many respects intermediate between the dog and hyena, and constitut- ing the type of a distinct family (Protelide), which is peculiar to the region. The tiger is absent, as it is, in fact, from the entire continent of Africa. The wolf and fox are also both wanting; but the latter is replaced in the Saharan and adjoining districts by the closely-related fennec (Fennecus). There is a remarkable development of the civets (Viverride), with a host of genera that are peculiar to the continent; the best known among these are the civets proper (Viverra), genets (Genetta), and the ichneumon (Herpestes), all of which, however, are found also beyond the limits of the region. Bears are entirely wanting, the only Afri- can representative of the Urside (Ursus Crowtheri) being extra- limital, a native of the Atlas Mountains. The Ethiopian Quadru- mana, or apes, constitute a part of the Old World group of the Catarhina, distinguished from the monkeys of the New World, as has already been stated in treating of the Neotropical realm, by the comparative narrowness of the nasal septum, the presence, in most cases, of ischial callosities and cheek-pouches, the universal absence of a prehensile tail, and the number of teeth, which never exceed the normal number (thirty-two) characteristic of the human species. This group comprises the most perfectly organised, or most hominine of the quadrumanous species, and, at the same time, those in which the fiercest and most savage disposition is combined with a less advanced structural development. As representatives of the former we have the anthropoid or man-like apes, constituting the family Simiade, which, in the African continent, comprises the chimpanzees and gorillas, and, in Asia and Malaysia, the gibbons and orang-outangs. The two species of chimpanzee (Troglodytes niger and T. calvus), as well as the gorilla (T. gorilla), are both re- stricted to the forest region of Equatorial Africa, especially the west coast; but it is still a matter of considerable uncertainty how far inland their range may extend. The researches of von Heuglin, 86 GEOGRAPHICAL DISTRIBUTION. Schweinfurth, and more recent travellers, seem ‘to show, almost beyond doubt, that the gorilla, which until recently was consid- ered to be limited in its haunts to the west-coast region—the forest tracts lying between about ten degrees of north latitude and the Gaboon River, including the Crystal Mountains—is in reality also an inhabitant of the deep interior of the continent, frequenting the forest recesses which bound the western tributaries of the Nile. Lower in the scale of organisation, but scarcely inferior in size in many cases to the anthropoid apes, are the dog-faced monkeys, constituting the family Cynopithecide. These, which embrace many of the most savage forms of all the monkey tribe, inhabit the greater portion of the Ethiopian region, the forests as well as the open plains and rocky fastnesses of mountain solitudes. Among the better known and more formidable members of this extensive family, which is also well represented in the Oriental region (macaques), and less numerously in the Austro-Malaysian (the islands of Batchian and Timor) and Tyrrhenian (the Barbary ape of the Rock of Gibraltar) transition regions, are the baboons, mandrills, chacmas, Diana monkeys, and mangabeys, the first three being characterised by a* prolonged snout, similar to that of the dog, at the extremity of which are situated the nostrils; the tail is rudimentary, or almost completely wanting. The Colobi constitute another extensive group of African apes. True monkeys, as well as the more distinctive of the African Mammalia—such as the lion, leopard, hyena, zebra, antelopes, giraffe, hippopotamus, and rhi- noceros—are wholly wanting in the Island of Madagascar, whose principal mammalian feature is constituted by the lemurs (Lemur- ide), or half-monkeys, a group of animals usually considered to form a sub-order of the Quadrumana, in certain peculiarities of structure closely approximating the most ancient progenitors of the ungulates. The presence of lemurs on the Island of Madagascar, the continent of Africa, and Southern India (with Ceylon), has led some naturalists to the conclusion that at one time direct land connection existed between the several regions, an assumption that is by some naturalists considered to be further borne out by other equally well-marked faunal characteristics. To this supposed formerly-existing land-mass of the Indian Ocean, which, if it ever existed, may or may not be represented in part by the sunken “Chagos Banks,” and the outlying islands, such as the Seychelles, FAUNA OF THE ETHIOPIAN REALM. 87 Laccadives, and Maldives, the name of ‘ Lemuria” has been given.* A very remarkable quadrumanous animal of the Island of Mada- gascar, and the only representative of its family, is the aye-aye (Cheiromys Madagascariensis), formerly described as a squirrel, which has many points of relationship with the rodents. The only other orders of Ethiopian Mammalia that need be specially referred to are the Proboscidea and the Edentata, the former represented by the African elephant (Loxodon Africanus), and the latter by the scaly ant-eaters (Manis, Pangolin), and the curious animals known as aard-varks (Orycteropus). The members of the genus Hyrax, which includes the shaphan or coney of the Bible, animals in several characters allied to the rodent on the one side, and the rhinoceroses, among pachyderms, on the other, constitute, in the opinion of many naturalists, a distinct order, Hyracoidea, apart by itself. Several species (Hyrax, Dendrohyrax) are recogrrised, all of about the size of the rabbit, and, with one exception, the coney, which is also found in Syria and Palestine, restricted to the African continent. The bird-fauna of the Ethiopian realm is by no means as rich, either in the actual number of its forms or in those that are pecu- liar, as the Neotropical. Neither do we find, as a rule, that brill- iancy and variety in the plumage which distinguish the birds of the South American continent, although gaudily-coloured birds are not exactly rare. Among these are the Irrisoride, a group of birds allied to the hoopoes, and remarkable for their metallic hues; the Meropide, or bee eaters, of which the common bee-eater of South- ern Europe (Merops. apiaster) is a well-known representative; and the curious forest-loving birds, known as the turacos and plantain- eaters (Corythaix, Musophaga), in a measure related to the South American toucans, constituting the family Musophagide. The Ethiopian region is the home, par excellence, of the insectivorous honey-suckers (Nectarinide +t), a family of birds bearing a super- ficial resemblance to the American hummers, which they also, in many cases, rival in the brilliancy of their plumage. The honey- guides (Indicatoride), formerly classed as cuckoos, and to an extent * It is here that, by some anthropologists, has been located the most an- cient abode of man. : + Also abundantly represented in the Australian and Oriental regions. 88 GEOGRAPHICAL DISTRIBUTION. partaking of their habits, but probably more closely related to the woodpeckers, are found in almost all parts of the region. The fly-catchers, warblers (Sylviade), true finches (Fringillidx), and weaver-birds (Ploceide) are numerically well represented, more especially the last, of whose two hundred and fifty, or more, species about two hundred are found within the limits of this region. This family comprises, among other birds, the small speckled and red- billed finches, known as the estrilds and amadines, the tailor-bird (Textor), the true weavers (Ploceus and Symplectes), and the long- tailed whydahs (Vidua), from the west coast. The parrots are but feebly represented in the Ethiopian region, the macaws and cocka- toos (Conurine and Cacatuide) being wholly wanting. With very few exceptions—Paleornis—all the African parrots belong to the group of the Psittacini, of which the common grey parrot (Psittacus erithacus) is a familiar example. No species is found to the north of the fifteenth parallel of north latitude. Of the gallinaceous birds there is a marked representation of the grouse tribe, especially of the genus Francolinus, and among the pheasants we have all the species of guinea-fowls (Numidinz), whose nearest allies appear to be the American turkeys. Birds of prey are very abundant, comprising, in addition to the common forms of vultures, eagles, &c., the hawk- like bird known as the “secretary” (Serpentarius), a near ally of the South American cariama. Finally, the Ethiopian region pos- sesses, although not exclusively, the ostriches (Struthio camelus, the common form, and 8. molybdophanes, from the Somali ter- ritory), of the family Struthionide. The reptile-fauna is very rich and varied, and comprises a con- siderable number of peculiar forms. Of Ophidia we have a large development of the vipers (Viperide), and among these one of the deadliest of venomous serpents, the puff-adder (Clotho). Of the larger constrictors, the rock-snake (Hortulia) and Seba’s python represent the Pythonide. The lizards comprise, among other sin- gular forms, the Agama, the typical Old World representative of the American iguanas, and the chameleon, with its distinctive changing hues. Crocodiles are met with in nearly all the larger streams. The fresh-water fishes of the African realm are limited, accord- ing to Ginther, to somewhat more than two hundred and fifty species, representing fiftcen distinct families or groups. About FAUNA OF THE ETHIOPIAN REALM. 89 sixty of these are siluroids (cat-fishes), fifty cyprinoids (carps), and about an equal number members of the family Mormyride. Owing to the broad distribution of the different types, which are spread throughout the greater extent of the continent, a division of the region into ichthyic sub-regions is rendered impossible. Of some fifty-six species found in the waters of the Upper Nile, no less than twenty-five are absolutely identical with forms belonging to the West African rivers, and doubtless most of these also occur in the waters of the unexplored tracts of the interior. Greater dissimi- larity exists between the northern and western faunas and those of the south, where the relationship has been rendered generic instead of specific. Thus, the fishes of Lake Nyassa and the Zambesi River are specifically distinct from those of the great equatorial lakes, and their outilowing northern and western waters. Africa has rep- resentatives of two genera of ganoid proper, Polypterus and Cala- moichthys, and one genus of lung-fishes, Protopterus (P. annectens), the last closely related to the Lepidosiren of South America. With the fish-fauna of this region the Ethiopian agrees in the partial possession of the characinids (about thirty-five species) and the chromids, and the genus Pimelodus among the cat-fishes. How the transference of similar or identical types was effected to such widely remote areas, whether through the intermedium of the waters of a continental tract now submerged beneath the Atlantic, or by way of the northern streams, it is impossible to say. The Ethiopian faunas, taken collectively, exhibit a remarkable homogeneousness throughout, so that the delimitation of even the three greater faunal sub-regions becomes difficult. The East Central African sub-region is, strictly speaking, representative of the entire tract, where the vast majority of all the distinctive types are found. The West African sub-region is more properly the home of the anthropoid apes, the chimpanzee and gorilla, and of the numerous species of Cercopithecus and Colobus. The antelopes are much less abundantly represented than in the plateau districts, although they comprise a number of peculiar types, especially of the bush- boks (Cephalophus). Other characteristic ungulates are the za- moose, a species of buffalo (Bubalus brachyceros—possibly also found in Abyssinia), the Hysmoschus aquaticus, and the Cheeropsis Li- beriensis (hippopotamus). The insectivores present as a distinctive type the otter-like Potamogale velox; the rodents the singular 90 GEOGRAPHICAL DISTRIBUTION. Anomalurus, recalling the fiying-squirrels ; and the edentates a distinct species or variety of aard-vark (Orycteropus Senegalensis). In the Saharan Desert tracts, where the necessary conditions for existence are largely wanting, there is a marked impoverishment of the fauna. The more formidable carnivores, such as the lion and leopard, are.absent from most districts, leaving their places to be filled by some minor cats, the hyena, jackal, fox, and fennec. The hoofed animals are represented (in some parts) by the buffalo, and a limited number of antelopes (Gazella, Oryx, Addax). Among rodents the families of rats and jumping-mice (Dipus, Scirtetes) are fairly represented, in addition to which we have the porcupine and hare (Lepus Mediterraneus). The ostrich is sufficiently abun- dant throughout most of the region. Among the desert reptilian forms may be mentioned the monitors (Varanids), scinks, sand- lizards (Sepide), and agamas. The deficiencies in the Madagascar mammalian-fauna have al- ready been indicated. As representative types we have, in addition to the lemurs and aye-aye, several civets (Galidia, Galictis), the singular cat-like carnivore known as Cryptoprocta (C. ferox), a water-hog (Potamocheerus), a sub-fossil species of hippopotamus, and the native hedgehogs (Centetide). The bird-fauna is made up largely of Asiatic and African types, although peculiar forms are abundant. Many of the reptilian forms, as the ophidian genera Heterodon, Herpetodryas, Philodryas, have American representa- tives. ORIENTAL REALM. This region comprises all that portion of the Asiatic continent which is not included in the Holarctic and Tyrrhenian tracts (ex- cepting the southern portion of the Peninsula of Arabia, which is Ethiopian), the Island of Ceylon, Formosa, the Philippines, Suma- tra, Java, and Borneo, besides some minor island groups. Within its limits are, therefore, included the whole of extra-Himalayan- Hindostan, Farther India, the Malay Peninsula, and that portion of China lying south of the Nanling range. A very considerable part of this region is covered with the most luxuriant forest growth, which extends even to an elevation of from eight to ten thousand feet along the slopes of the Himalaya. This forest character more particularly distinguishes the Indo-Chinese and Indo-Malayan sub- INDIAN MAMMALIA. 91 regions, the former of which includes Burmah, Siam, Anam, South- ern China, the southern Himalaya slopes, and the luxuriant tracts lying along the base of these mountains, known as the “ Terai”; and the latter, the Malay Peninsula, with the Indo-Malaysian islands already mentioned. A third sub-region, the Indian, is constituted by the Indian Peninsula, exclusive of the Carnatic. The surface here consists largely of open pasture or grass lands, the funda- ment being in great part the alluvium of the existing rivers. In the northwestern part, bounded by and partly lying within the valley of the Indus, is the Indian Desert, where we encounter a considerable intermixture of strictly Indian, Holarctic, and Ethio- pian animal types. An essentially forest character again distin- guishes the southern extremity of the Indian Peninsula—the Car- natic—and the Island of Ceylon, which together form the fourth sub-region, the Cingalese. Zoological Characters of the Oriental Region. — A cursory examination of the Oriental mammalian fauna shows it to be largely made up of characteristic African forms, for which reason, indeed, some naturalists have been induced to unite this region, either in whole or in great part, with the Ethiopian. We have here the same extraordinary development of the quadrumanous, carnivore, and ungulate types, although in respect of these last very material differ- ences present themselves which are sufficiently distinctive of the two regions. Thus, in the Oriental region there are no representatives of either the Camelopardelide or Hippopotamide, families peculiar to the African continent; and the only member of the Equide—the horses, asses, and zebras—the onager (Equus onager), is found in the debatable land along the Indus, which unites the Oriental and Holarctic tracts. There is also a great falling off in the number of antelopes, of which there are scarcely more than a half-dozen species—comprising among others the gazelle, the true antelope, and nylghau ; but their place is in great measure taken by the solid-horned ruminants, the deer, which, as has been seen, are completely wanting in the Ethiopian region, but have here no less than about twenty species, ranging in size from the diminutive muntjac (Cervulus) to the giant rusa. This is also the home of the beautiful axis. The chevrotains or mouse-deer (Tragulidex), a small group of diminutive deer-like animals characterised by the presence of tusks in the upper jaw, have but one extra-limital 92 GEOGRAPHICAL DISTRIBUTION. representative, the Hyemoschus, from Western Africa, already re- ferred to. Of the oxen we have the Indian buffalo (Bubalus Indicus or buffelus), whose range at the present day (as a domestic animal) comprises, in addition to its native haunts, a considerable part of Northern Africa and Southern Europe (Hungary, Greece, Italy), and three or four species of wild cattle—the gaour, gayal (Bibos)— distributed over the greater portion of the region, from Java to the Indian Peninsula. The sacred cow or Brahmin bull, commonly known as the zebu, is now found only in a domesticated state. The goats have but a single representative in the entire region—in the Neilgherry hills; the sheep are completely wanting. The thick- skinned ungulates are represented by four or five species of rhi- noceros, both one- and two-horned, whose most eastward abode appears to be the Island of Java; a solitary species of the South American family of tapirs (Tapirus Malayanus), and about six species of swine (Suide). Of the Carnivora there is, as in the Lthiopian region, a large development of the civet-cats (Viverride), most of the genera representing the family in this region being pe- culiar to it (Viverricula, Paradoxurus, Arctogale, Cynogale). The Mustelide comprise several well-known Holarctic forms, such as the true weasel (Mustela), martin (Martes), otter (Lutra), and badger (Meles), the last found only in Southern China. The cats (Felide) are represented by many of the more prominent types of the Ethiopian region—such as the lion, leopard, and panther—in addition to which we have the ounce and tiger, the latter extend- ing its range as far north as the fifty-third parallel of latitude (Lake Baikal), and westward to the borders of the Caspian Sea. It is found in the islands of Java, Sumatra, Bali, and Saghalien, but is absent from both Ceylon and Borneo. The dogs (Canidae) differ in several respects from the representatives of the same group of animals entering into the Ethiopian fauna, and are more nearly allied to the Holarctic forms. The true wolf is absent; but its place is filled by several races of closely-allied wild-dogs, which hunt wolf-like in packs over certain portions of the region, and the jackal. The fox is represented by several species. Only one of the three recognised species of hyena, the striped hyena (Hyena striata), whose range embraces the entire northern part of the con- tinent of Africa and a considerable portion of Western: Asia, en- ters into the region. One primary distinguishing feature separating INDIAN MAMMALIA. 93 the carnivore-fauna of the Oriental region from that of the Ethio- pian is the presence in the former of bears, which comprise here not only the singular forms known as the sun-bears (Helarctos), confined to the Indo-Malayan sub-region, and the honey-bears (Me- lursus), whose range extends from the Ganges to Ceylon, but also the true bears of the genus Ursus. The Indian elephant inhabits nearly all the wooded tracts from the Himalaya slopes to Ceylon, and east- ward to Borneo and Sumatra.* The Oriental region is, par excel- lence, the headquarters of the true mice and squirrels, there being no less than about fifty specific representatives to each of the genera Mus and Sciurus, or about one-half the number of all the forms that have been ascribed to these genera. Both the round- and flat- tailed flying squirrels (Pteromys, Sciuropterus) are distributed throughout the region, the former, with the exception of three or four extra-limital species found in Japan, being restricted to it, and the latter distributed throughout a considerable portion of the Holarctic region, and on both sides of the Atlantic. The marmot is found in the debatable lands of the Western Himalayas, at heights exceeding eight thousand feet. The bats have a much more extended development in this region than in any other, except the Neotropical, there being upwards of one hundred distinct spe- cific representatives. These include members of all the generally recognised families except the Phyllostomide, or simple leaf-nosed bats (to which the South American vampyres belong), and conse- quently embrace the short- and long-eared bats, the horse-shoe bats, and the fruit-eating bats (Pteropide), commonly known as flying- foxes. The most important of the Oriental Quadrumana are the macaques (Macacus), to which the Barbary ape of the Rock of Gib- raltar belongs, and which inhabit the entire region, and the long- tailed Semnopithecus, which has nearly the same range, and several of whose representatives inhabit the more elevated forests, even during the winter, at heights exceeding eleven thousand feet. To this genus belongs the peculiar Bornean ‘‘nose-monkey” (S. nasa- lis). The anthropoid apes are confined to the southeastern portion _ of the region, and principally to the larger islands of the Malay * The Javanese elephants do not appear to be indigenous to the Island of Java. The Sumatra elephant, which was considered by Professor Schlegel to represent a distinct species apart from the Indian (Elephas Sumatrensis), is now usually referred to the latter species. 94. GEOGRAPHICAL DISTRIBUTION. Archipelago. They comprise one or two species of Orang (Borneo and Sumatra), the long-armed gibbons (Hylobates), whose range extends from Java to Assam and China, and the siamang, a native of Sumatra and the Malay Peninsula, The half-monkeys, or lemurs (Nycticebus, Stenops), which were found to be so charac- teristic of the Madagascar fauna, show a very great diminution in numbers in the Oriental region. Their most distinctive or anom- alous type is the tarsicr or spectrum lemur (Tarsius spectrum), an inhabitant of Sumatra, Borneo, and Celebes (Austro-Malaysian), which of itself constitutes a distinct family (Tarsiidm). In the structure of its feet—the extraordinary and unequal development of the toes—and in several other peculiarities it is closely related to the aye-aye, from which to the true lemurs it appears to form a passage. Until recently classed with the lemurs, but now con- sidered as representing the type of a distinct family of insectivorous animals, are the cat-monkeys or flying-lemurs (Galeopithecus), which inhabit the larger islands of the Malay Archipelago and the Philippines. The bird-fauna of the Oriental region is exceedingly rich and varied, and, as might have been expected from its position, com- prises in its assemblage a very large proportion of Holarctic, Ethio- pian, and Australian forms, But the number of distinctive forms are sufficiently numerous, and eminently serve to characterise the region. Among these are the laughing or babbling thrushcs (Timal- idm), a family which, though not absolutely restricted to the region, has its headquarters there. Nearly two hundred of the two hundred and fifty described species occur here, and are found in nearly all parts of the region. Less numerous in species, but scarcely less distinctive, are the Leiotrichidw, or hill-tits, found in all parts of the Himalaya Mountains; the Pycnodontide, or bul- buls,; Phyllornithidw, or green bulbuls; and the minivets of the genus Pericrocotus, one of the group of caterpillar-caters. Of the - warblers (Sylviads), the peculiar tailor-bird (Orthotomus) has about thirteen to fifteen species. The starlings are represented, among other forms, by the sacred mynah (Eulabes) and the roseate pastor (Pastor roseus); the bee-eaters by Merops and the resplendent Nyctiornis; the sun-birds (Nectarinid) by the Nectarophila and Arechnothera. The flower-peckers (Dicside), a group of small, gaily-coloured birds representing the South American sugar-birds, BIRDS OF THE ORIENTAL REALM. 95 are tolerably abundant throughout the greater portion of the re- gion. The South American cotingas likewise appear to have their representatives in the large and gaudy broad-bills (Eurylem- idz). Trogons, scarcely inferior in the beauty of their plumage to their American congeners. are sufficiently abundant in the for- est districts, where, also, we mect with a multitude of the remark- able horn-bills. Contrary to what might have been expected, seeing their abundance in the Australian region (and partially so also in the Ethiopian), and the apparently favourable conditions for their existence here, the parrots are but feebly represented, and belong, with one exception—a cockatoo from the Philippine Islands, the only one found within the limits of the region—to the family of the ringed-parakeets (Paleornithide). Of the gallinaceous birds the pheasants (Phasianide) are largely represented. This is the home of the jungle-fowl (Gallus), from one of whose species, the G. Bankiva, inhabiting the region from the Himalayas through Central India eastward to the islands of Java and Timor, is in all probability descended the greater portion of our domestic poultry. Distinct species of the jungle-fowl are found in Southern Hindo- stan, Ceylon, and Java, and, possibly, some of the domestic varieties may have been produced as the result of interbreeding between these various forms and the G. Bankiva. The peacock is found throughout a considerable portion of the region, to which it is indigenous, from Ceylon to the Himalayas, and eastward to China; belonging to the same family, and scarcely less resplendent in their plumage, are the argus, impeyan, tragopan, and fire-backed pheas- ants. The remarkable group of Australian birds known as ‘‘mound- builders,” megapods, or brush-turkeys, constituting the family Megapodide, which would seem to be closely related to the South American curassows, have two representatives (of the genus Mega- podius), one, possibly introduced, in the Nicobar Islands, and the other in the Philippines and Borneo. The reptilian-fauna comprises, among’other serpents, the giant python (of the family Pythonide), the cobra-di-capello (of the family Elapide, or coral-snakes), and one-half of all the pit-vipers, or members of the family of rattlesnakes (Crotalide), although the rattlesnake proper is absent; among lizards, the Varanide, or water-lizards, to which the monitor belongs, the geckoes, the agamas, or eastern iguanas, the last embracing no less than eighteen 96 GEOGRAPHICAL DISTRIBUTION. species of so-called fiying-lizards (Draco), animals provided with a lateral expanded tegumentary membrane ; and of crocodilians, the true crocodile (Crocodilus) and the gavial (Gavialis), the latter restricted to the rivers of the Indian Peninsula. The several faunal sub-regions, especially those of the conti- nentai tract, are most intimately related to one another, and do not admit of sharp delimitation. Yet a number of forms, whether negatively or positively, may be said to define each. Thus, among the Mammalia, the lion, hyena, fox, lynx, mellivore, buffalo, nyl- ghau, gazelle, and true antelope, may be said to represent distinct- ive types of the first, or Indian sub-region, being absolutely restrict- ed to it, or just passing beyond its confines. The Cingalese sub- region is characterised, among other forms, by the loris, which it alone possesses; by a peculiar genus of civet-cats (Onychogale), and Platacamthomys among the mice. The fauna, especially of the island of Ceylon itself, is related on the one side to that of the Himalayas, and on the other to that of the Indo-Malayan sub-region, differing broadly from the fauna of the central and northern por- tions of the Indian Peninsula. The relationship with the Malayan fauna is especially marked in the case of the Lepidoptera and Cole- optera among insects, many of the more distinctive or abundantly represented types belonging exclusively to the two faunas under consideration. The individuality of the Cingalese reptilian and amphibian faunas is well marked through the number and variety of peculiar genera, which, perhaps, more than any other animals, serve to characterise the sub-region. All the members of the Uropeltidx, or rough-tailed burrowing-snakes, appear to be con- fined to this tract. The poisonous snakes of the entire peninsula of India are, according to Fayrer, comprised in eleven genera, rep- resenting three families, Elapide, Viperidew, and Crotalide (pit- vipers), and some twenty-five species. Among the more venomous forms are Naja (the cobra, which ascends the Himalayas to a height of eight thousand feet), Ophiophagus, and Bungarus, of the Ela- pide; Daboia and Echis representing the vipers; and Trimeresurus belonging to the pit-vipers. In addition to the terrestrial Thanato- phidia the marine-snakes (Hydrophide), which inhabit brackish estuaries and tide-water streams, furnish an additional contingent of thirty-five or more species. The two remaining sub-regions, the Indo-Chinese and the Indo- AUSTRALIAN REALM. 9% Malayan, are most intimately related to each other in the general characters of their faunas, as they are also to the Indian; the former, however, incorporates a more decidedly Holarctic element, while the latter is almost strictly tropical. Among the more distinctive mammalian types of the Indo-Chinese tract, or such as do not enter into the composition of the Malayan fauna, are the true bears (Ur- sus), panda (Ailurus), fox, badger, Arctonyx (Melide), and a pecu- liar genus of civet-cats, Urva. On the other hand, this tract is wanting in the anthropoid apes of the genera Simia (orang—Borneo and Sumatra) and Siamanga (Malacca, Sumatra), the spectre-lemurs (Tarsius— Sumatra, Borneo), flying-lemur (Galeopithecus), tapir (Tapirus Malayanus—Malay Peninsula, Sumatra, Borneo), and sun- bear (Helarctos), which belong to the Malayan fauna. The Hima- layan districts (with parts of China) are preeminently the home of the pheasants, which, in addition to several genera peculiar to the Oriental region (Pavo, Argusianus, Polyplectron, Euplocamus), comprise a number of forms, the impeyan, tragopan, &c., held in common with the Holarctic; the peacock ranges from Ceylon and the Himalayas to Java, and the argus from Siam to Borneo. THE AUSTRALIAN REALM. This region, as usually defined, embraces, in addition to the continent of Australia and the Island of Tasmania, all the Austro- Malaysian islands lying to the east of Borneo and Bali—i. ¢., begin- ning with Celebes and Lombok—the vast Polynesian Archipelago, and New Zealand, with its accompanying islets. This last has by some naturalists, and more especially by Professor Huxley, been rec- ognised as a distinct region, although by the majority of zoogeogra- phers it is usually regarded as a sub-region of the Australian. In this place only Australia proper (with Tasmania), Papua (New Guinea, and the minor Papuan islands), and New Zealand are con- sidered to enter into the formation of the Australian region. The greater portion of the Australian mainland consists of a table-land of moderate elevation, characterised by a harsh and dry climate, and a general absence of water. Hence the surface of the country bears a more or less barren aspect, supporting but a scant vegetable growth, which is parched throughout the greater part of the year, and consequently rendered unfit for promoting a vigorous development of animal life. A considerable part of the tract passes 8 98 GEOGRAPHICAL DISTRIBUTION. off into an almost uninhabitable desert. Along the coast-line, and more especially on the eastern border, where vapour-condensing sur- faces present themselves in the form of elevated mountain-crests, there is an abundance of aqueous precipitation, to which a luxuri- ous forest-growth responds. Less than one-half of the continent lies within the tropics. Papua, which constitutes the second sub- region, exhibits in great part a mountainous character, and, from the abundance of aqueous precipitation distinctive of the equatorial portions of the earth’s surface, a vegetation of truly tropical luxuri- ance. A dense forest growth likewise covers the greater portion of New Zealand (third sub-region), where also we have the most elevated mountain-summits in the region. Zoological Characters of the Australian Realm.—The Aus- tralian region is, by both positive and negative characters, the most marked of any on the earth, and, indeed, so remarkable are its faunal peculiarities that it has been thought by some to constitute properly in itself a main zoogeographical division, as opposed to the rest of the world. The most striking feature of this fauna is the general absence, among the Mammalia, of such forms as, under favourable conditions, are to be met with in all other portions of the earth’s surface. In the whole of this region all the terrestrial Mammalia that are to be found in the Old World are absent, except a solitary (possibly two) species of hog (Sus), found in New Guinea, the bats, and rodents, the former being represented by about ten genera, and the latter by the single family of the mice (Muride), of which the true mice (Mus) comprise more than one-third of all the vari- ous forms. The edentates, insectivores, carnivores, and monkeys, except such as have been introduced through the. agency of man, and possibly the “ dingo,” or Australian wild-dog, which may prove to be indigenous, are wholly wanting, their place being filled by a wonderful variety of the implacental mammals—the marsupials and monotremes—the lowest of the entire mammalian series. No im- placental mammals occur at the present time in any portion of the Old World outside of the limits of the Australian and the connect- ing Austro-Malaysian regions, and their only representatives in the Western Hemisphere are the opossums (Didelphyid), upwards of twenty species of which range throughout the forest districts of the Neotropical realm (with two species in North America). The Aus- tralian marsupials fall into six distinct families: The Macropodide, AUSTRALIAN MAMMALIA, 99 kangaroos and kangaroo-rats, are numerically the most important and the most broadly distributed of the several types, and com- prise a diversity of forms, which are variously adapted to living in the scrub, in the desert, along rocky and precipitous mountain summits (Petrogale), or on trees. The arboreal genus Dendrolagus is thus far known only from New Guinea and Queensland. The great kangaroo (Macropus giganteus), inhabiting the southern half of the continent of Australia and Tasmania, attains in the male a length, from the tip of the nose to the root of the tail, of upwards of five feet. The kangaroo-rats, rat-kangaroos, or potoroos (Hypsi- prymnus), are diminutive forms, of about the size of a hare, with rounded instead of elongated ears, and a general rat-like appearance. The second family is that of the Dasyuride, or native cats, a group of carnivorous and insectivorous marsupials, which range in size from the dimensions of a mouse to those of a wolf. The most dis- tinctive forms belong to the genus Antechinus, a group of insect- ivorous animals, which, in outward appearance, are but barely dis- tinguishable from the ordinary mice. The most formidable member of the family is the Tasmanian “tiger,” or “ hyena” (Thylacinus cynocephalus), a striped carnivorous marsupial, having the general aspect of a wolf or dog, which it also fully equals in size, measuring as much as five feet in length. The third family is that of the Myrmecobiidz, which includes but a single species, the native ant- eater, or striped myrmecobius (M. fasciatus), a small squirrel-like animal, of about the size of the common squirrel, inhabiting South- ern and Western Australia. The Paramelide comprise the bandi- coots (Perameles), small kangaroo-like animals of about the size of the rabbit, and the singular pig-footed marsupial known as the Cheropus, a graceful animal somewhat recalling in appearance the mouse-deer of the Oriental region. The fifth family, the Pha- langistide, exhibits in its individual components a greater diversity of form, and greater specialisation of structure, than is to be found in any other mammalian family. As described by Wallace, we find represented in this family the tailless koala, or native sloth (Phas- colarctos); the prehensile-tailed opossum-like phalangers (Phalan- gista); the beautiful flying-opossums (Petaurista, Belideus, Acro- bata), so closely resembling in form the flying-squirrels of North America and India, but often no larger than a mouse, the dormouse- like Dromicia, one species of which does not equal in size the ordi- 100 GEOGRAPHICAL DISTRIBUTION. nary harvest-mouse; and, finally, the little Tarsipes, a true honey- sucker, provided with an extensile tongue, and of the size of a mouse. All of these-various forms are more or less adapted to an arboreal existence. The remaining family of the marsupials is that of the wombats (Phascolomyide), nocturnal burrowing animals of about the size of the badger, and somewhat of the appearance of a bear, subsisting chiefly on roots and grasses. The most anomalous and remarkable of all the Australian mammals, indeed of all Mam- malia, are the oviparous monotremes—the duck-bill (Ornitho- rhynchus) and native hedge-hog (Echidna)—strictly speaking, bur- rowing edentate animals, having certain points of affinity with both birds and reptiles. With few exceptions (Cuscus, Belideus), all the marsupial genera of the Australian region are confined to the continent of Australia, Tasmania, and New Guinea (and the Aru Islands), but a very insignificant fraction of the entire number of marsupial species being represented in any of the Austro-Malaysian islands (Mysol, Celebes). Even in New Guinea, as compared with Australia, the number of such representatives is rather limited; but we here meet with at least one type of placental mammal, the hog, which is not met with on the continent of Australia. On the other hand, the (in Australia) fairly well represented family of rats and mice exhibits in the Papuan sub-region (Aru Islands) but a solitary example, the Uromys. In respect of its bird-fauna, the Australian region presents us with peculiarities that are scarcely less marked than those which distinguish the Mammalia. In the number and beauty of its forms this region is only second to the Neotropical, while in such as show the most marked peculiarities of structure it is unsurpassed. Many of the most familiar types of Old World birds are repre- sented, and in sufficient number—such as the warblers, thrushes, fly-catchers, shrikes, and crows; but, on the other hand, some of the most broadly diffused families are wholly wanting. Thus, the true finches (Fringillide), which have otherwise a universal dis- tribution, appear to be wanting in all parts of the region, being replaced by the weaver-finches (Ploceidw). The vultures are also completely absent, as are likewise the woodpeckers (Picidew) and pheasants (Phasianidx). The true paradise-birds (Paradiseine), whose special development in New Guinea and the other Papuan Islands forms such a marked feature in the avian-fauna of that sub- BIRDS OF THE AUSTRALIAN REALM. 101 region, have but two representatives (Manucodia) on the Australian mainland; the bower-birds (Tectonarching), on the other hand— members of the same family—have here their greatest development (seven species), and are associated with two species of rifle-birds (Ptiloris). The Australian region is distinguished by being the sole possessor of the families of lyre-birds (Menuride) and apteryxes (Apterygide), the latter one of the most remarkable groups of ex- isting birds (natives of New Zealand), whose exact relationships have not yet been satisfactorily determined. The struthious birds of the genus Dromezus, the emu (two species), are confined to the continent of Australia, as is also one of the genera of brush-turkeys (Leipoa). Talegallus, the true brush-turkey, and Megapodius, the megapod or mound-builder, have both representatives in the Papuan Islands and Australia, the former being restricted to the region under consideration. The greater number of the species of Mega- podide, some twenty or more, are distributed throughout the Austro-Malaysian islands and Polynesia, with two outlying species in the Philippines, Borneo, and the Nicobar Islands. The parrots have an extensive development, and represent in the main forms that are not known beyond the limits of this and the transition region. ‘No group of birds gives to Australia so tropical and foreign an air as the numerous species of this great family, by which it is tenanted, each and all of which are individually very abundant. Immense flocks of white cockatoos are sometimes seen perched among the green foliage of the lofticst trees; the brilliant scarlet breasts of the rose-hills blaze forth from the yellow flowering Acacie; the Trichoglossi or honey-eating parakeets enliven the flowering branches of the larger Eucalypti with their beauty and their lively actions; the little grass parakeets rise from the plains of the interior and render these solitary spots a world of anima- tion; nay, the very towns, particularly Hobart Town and Adelaide, are constantly visited by flights of this beautiful tribe of birds, which traverse the streets with arrow-like swiftness, and chase each other precisely after the manner the Cypseli are seen to do in our own islands. In Tasmania I have seen flocks of from fifty to a hundred of the Platycercus flaviventris, like tame pigeons, at the barn-doors in the farm-yards of the settlers, to which they descend for the refuse grain thrown out with the straw by the threshers.** ” About sixty species of the order are known from the mainland of 102 GEOGRAPHICAL DISTRIBUTION. Australia alone. The Cacatuide, which are found only in this and the adjoining transition region, with a solitary species, Caca- tua hematuropygia, in the Philippines, comprise, among other forms, the commoner species of the genus Cacatua, as the sulphur-crested and rose-breasted cockatoos, and the black cockatoos of the genus Calyptorhynchus, which last are restricted to the continent of Aus- tralia and Tasmania. An aberrant group of the parrots are the New Zealand nestors (Nestoride), some of whose members appear to be addicted to carnivorous habits,*® and which would seem to have certain points of relationship with the South American ma- caws. In New Zealand, likewise, are found the owl-like nocturnal parrots of the family Strigopide. One of the most distinctive groups of birds of the Australian region are the honey-suckers (Meliphagide), whose representatives are scattered all over the Austro-Malaysian and Polynesian groups of islands, from Celebes to the Marquesas Islands, and from Tasmania to Hawaii. Of some two hundred or more species of this family but a single one, Ptilotis limbata, enters the Oriental region (the Island of Bali). The nearly related honey-suckers (Nectarinide) are represented by several forms more or less distinctive of the region (Arachnecthra, Arachnothera). Australia with New Guinea, and the adjacent isl- ands, may be considered to be par excellence the natural home of the pigeons (Columbs), nearly one-half of the total number of genera (forty or more) being represented here, and by types many of which are found nowhere else. They include the most gaudily ornamental representatives of the order (Ptilopus), which in the brilliancy of their plumage yield but little to the parrots ; various forms of ground-pigeons (Geophaps, &c.); and the beautiful crested- pigeon known as the goura, from New Guinea and some of the adjacent islands. The turtle-dove (Turtur) is found in New Guinea, but the nearly universally distributed Columba, to which the or- dinary rock- or wild-pigeon (C. livia) belongs, and which represents the ancestral form of most of our domestic breeds, is wanting. The reptile-fauna of this region is much less distinctive than either the mammalian or avian. Snakes, amphibians (but only the tailless forms), and lizards are abundant, the great bulk of the last being constituted by the scinks and geckoes. Of the amphibians the true toads (Bufonide) are represented by a limited number of species in Australia, although the genus Bufo itself is wanting; POLYNESIAN REALM. 103 Rana, the frog, has a single species on the peninsula of York (R. Papua), but is more abundant in New Guinea. Tree-frogs (Hyla) are numerous. A peculiarity distinguishing the continental ophidian fauna is the great preponderance of venomous over non-venomous serpents. The proportion of the former to the latter is in some sections, as in South Australia, as six to one. Two-thirds of all the species belong to the family Elapide, to which the American coral-snakes and the Indian cobra also belong. One species of crocodile is found in some of the Australian waters. The fish-fauna is very limited, less than forty species being known from the entire realm. Two species of lung-fishes, the ‘‘barramundas” (Ceratodus Forsteri and C. miolepis), inhabit the waters of Queensland. The paucity of forms is, doubtless, in part attributable to the limited number of fresh-water streams. THE POLYNESIAN REALM. The scattered island groups of the Pacific Ocean are so deficient in the faunal elements that distinguish the main zoogeographical divisions of the earth that they may be said to constitute a region framed more by negative than by positive characters. For this reason they have by many naturalists been relegated to the rank of a mere sub-region. Yet, when we compare the Polynesian fauna with the faunas of the other recognised regions, it becomes not a little difficult to determine just where it should be placed, although there would seem to be hardly a question as to the preponderating relationship being with the Australian fauna, with which it has generally been united. The addition, however, of so enormous an annex to a region which combines in its faunal elements such a remarkable individuality, and with which, after all, there is not very much in common, does not appear natural; and the less so, when we recognise the full importance of the characters derived by the Polynesian tract from regions other than the Australian, and its own special peculiarities. For these reasons it seems advisable to consider the region as one apart by itself. Zoological Characters of the Polynesian Realm.—This tract is at once distinguished from the Australian, as well as from all others, by the abscence of all Mammalia excepting bats. Of these last there are representatives of two families, the Oriental fruit- 104 GEOGRAPHICAL DISTRIBUTION. eating bats, or flying-foxes (Pteropide), and the cosmopolitan Ves- pertilionide, distributed almost everywhere throughout the region. The flying-foxes are, however, absent from both New Zealand and the Sandwich Islands. The more important families of birds are mainly such as have an extensive representation in the Australian realm, or are held in common by this and the Oriental or Ethio- pian realm. Among these are the caterpillar-eaters (Campephagi- da), flower-peckers (Dicewidx), weavers (Ploceide), and swallow- shrikes (Artamide). With insignificant exceptions all the families of birds that are wanting in the Australian region are likewise wanting here; in addition to which, several of the more representa- tive families of Australian birds, as the birds-of-paradise, bower- birds, lyre-birds, cassowaries, cockatoos, and apteryxes, are also wanting. On the other hand, the region contains three families which are absolutely confined to it; these are the dodo-pigeons (Didunculidz), from the Samoan Islands, the Drepanidew, from the Sandwich Islands, and the heron-like Rhinochetidw, from New Caledonia. The mound-builders (Megapodidw) and honey-suck- ers (Meliphagids) have a very extensive distribution. The more nearly cosmopolitan families include among others the thrushes, warblers, crows, cuckoos, king-fishers, swallows, goat-suckers, swifts, pigeons, falcons, owls, and herons. Most of the genera of Sand- wich Island birds are peculiar; hence it might be considered doubtful whether the tract inhabited by them should properly be considered to constitute a part of the region under considera- tion. The reptile-fauna is feebly developed. Lizards, principally geckoes and scinks, range throughout the greater part of the region, as do likewise a very limited number of serpents, which are, however, absent from the more distant islands. The appear- ance of a member of the American family of Iguanid# (Brachylo- phus) in the Feejee Islands is not a little surprising. Three species of Cornufer (Ranide) inhabit the Feejee Islands, and Bufo dialo- phus apparently the Sandwich Islands, but otherwise the Amphibia are almost wholly wanting. The fresh-water fishes are very limited in number, and exhibit a remarkable sameness throughout, com- prising principally such forms—eels, atherines, mullets, gobies— as can readily accommodate themselves to brackish-water condi- tions. A siluroid (Arius) is found in the Sandwich Islands. TYRRHENIAN TRANSITION REGION. 105 THE TYRRHENIAN TRANSITION REGION. The fauna of this region is an association of elements derived from the faunas of the Holarctic, Ethiopian, and Oriental realms, with a preponderance on the north side of the Mediterranean of the Holarctic element, and on the south side probably of the Ethio- pian. The number of absolutely peculiar forms, or of forms which barely pass beyond the confines of this.tract, is not great. Among the Mammalia we have three such genera: Dama, the fallow-deer, found on both sides of the Mediterranean; Addax, an antelope, confined to North Africa and Syria; and Psammomys, a mouse, restricted to Egypt and Palestine. By far the greater number of the mammalian types occurring on the north side of the Medi- terranean are such as might be considered to belong to the Euro- pean division of the Holarctic tract; but yet there are a con- siderable number of both genera and species which are entirely or nearly unknown there, and which either represent peculiarities, or forms belonging to the more tropical regions to the south. Such are the genet, ichneumon (found in Spain), porcupine, jackal (Dalmatia), Corsican deer (Cervus Corsicanus), and moufflon (Cor- sica, Sardinia, Crete, mountains of Greece). Until quite recently, too, the indigenous animals included also the lion and hyena. The ape of the Rock of Gibraltar (Macacus Inuus), although found on the Barbary coast, is more strictly an Oriental type. The Ethio- pian affinities are further established on the African and Asiatic sides by the elephant-shrews (Macroscelididz), coney (Syria), the antelopes of the genera Oryx, Alcephalus, and Gazella, and several additional members of the larger Carnivora—leopard, serval, and hunting-leopard. In the early part of this century the hippopota- mus still inhabited Lower Egypt. The wild-asses which inhabit the desert plains included between the Red Sea and the Indus River may be considered as a link between the Holarctic and Ethiopian faunas. The bird-fauna is on the whole very much more nearly Hol- arctic than anything else, a very large proportion of the species being such as inhabit Europe north of the Alps. But this is due in considerable part to the interchanges which are effected through the northerly and southerly migrations. According to Canon Tristram,® no less than two hundred and sixty out of three 106 GEOGRAPHICAL DISTRIBUTION. hundred and twenty-two species of birds inhabiting Palestine are European forms, one hundred and thirty-four species (land and water birds) being common to Britain and Palestine. Of the Per- sian avi-fauna one hundred and twenty-seven species are also found in Europe." Of the Oriental and Ethiopian birds which are not known north of, or barely transgress, the Tyrrhenian tract, may be mentioned the francolin, the quail-like Turnix, pastor, honey- sucker (Nectarinea), hoopoe (Upupa), oriole, Ceryle and Halcyon among the kingfishers, the bee-eater (Merops), flamingo, and the genera Gyps, Vultur, and Neophron among the vultures. The ostrich enters the desert regions of Syria. The reptilian and amphibian faunas contain a very considerable number of forms peculiar to the region. Of some fifty-three species found in Italy, only twenty-six penetrate into the region north of the Alps, and of this number from five to eight also enter the Ethiopian region.” According to Béttger, of the forty species inhabiting Morocco, twenty-two also belong to Spain, and but seven of these pass into the northerly Holarctic tract. On'the other hand, only eight of the Moroccan species are known to inhabit the Ethiopian region. Algeria, according to the researches of Strauch, is repre- sented by seventy-six species, of which twenty-seven are also Italian, and but ten Holarctic. On the other hand, eleven species are positively known to inhabit the Ethiopian region, and, according to Forsyth Major, not unlikely eighteen others will also be found to do so.* THE SONORAN TRANSITION REGION. This tract, which, as already stated, comprises the peninsula of Lower California, the State of Sonora in Mexico, New Mexico, Ari- zona, and parts, not yet absolutely defined, of Nevada, California, Texas, and Florida, is, as far as the Mammalia and birds are con- cerned, not very clearly differentiated ; the intermingling of northern and southern elements, with a decided preponderance in favor of the former, is very great, and the peculiarities insignificant. Two species of Bassaris, a member of the raccoon family, appear to be confined to California, Texas, and the highlands of Mexico. Among the more peculiarly Neotropical forms that enter the tract are the jaguar, the peccary, a solitary species of armadillo, and a bat of the genus Nyctinomus. The reptilian and amphibian faunas are much AUSTRO-MALAYSIAN TRANSITION REGION. 107 more distinctly of a southern than of a northern facies. Of some filty-five or more species of lacertilians, very nearly three-fourths of the number are iguanas (Iguanide), and four are geckoes. Fully one-half of the total number of genera represented are not found in other portions of the North American continent. The serpent- fauna comprises about twenty-two genera, one-half of which are peculiar. Eleven of the thirteen species of North American rattle- snake are found here ; the otherwise common coluber is wanting. Among the tailless amphibians, the Bufonide (Bufo) have their headquarters here, more than one-half of all the North American species being represented. The tree-frogs (Hylidw), and frogs proper (Ranidee), are, on the other hand, both very deficient. The tailed amphibians, of which there are upwards of fifty species in the region to the north, are almost completely wanting. ** THE AUSTRO-MALAYSIAN TRANSITION REGION. This region, which is situated intermediately between the Ori- ental and Australian realms, naturally partakes of an intermediate position also in respect of its fauna. While the animal types bor- rowed from the adjoining regions preponderate to a very marked extent, the number of specific forms that are absolutely peculiar, especially among birds, is very remarkable. According to Mr. Wallace nearly three-fourths of some two hundred species of land- birds inhabiting the Moluccas are peculiar to those islands, and very nearly one-half of a hundred and fifty or more species found on the island of Celebes are absolutely confined to it. Yet, of the one hundred and twenty genera here represented (Celebes), only nine are peculiar. With few exceptions, all the families of birds that are represented in either the Australian or the Oriental region are also represented here. As belonging to the former, the birds-of- paradise have but a single species, the standard-wing (Semioptera Wallacei), found in the islands of Gilolo and Batchian; the honey- suckers appear to be almost entirely absent from ‘Celebes, although they are to be found in several of the other islands. The Oriental babbling-thrushes (Timalidz) and bulbuls (Pycnonotide) barely en- ter, while the hill-tits (Leiotrichide) are completely wanting. It is not a little remarkable that the creepers (Certhiade), stone-hatches (Sittide), and tits (Paride), which have their representatives in “4 108 GEOGRAPHICAL DISTRIBUTION. the regions on either side of this one, should be entirely wanting here. The placental Mammalia are represented by about twenty species, exclusive of the Cheiroptera, mainly of Asiatic types. ‘Six- teen of these are found on the island of Celebes, and comprise sev- eral rodents (mice and squirrels), a wild-hog, a deer (Cervus hip- pelaphus), very closely related to, if not identical with, a Javan species; a civet-cat, a spectre-lemur (Tarsius spectrum), and three peculiar forms, unlike anything found either on the continent of Asia or the Malayan islands. These are a black and almost tailless baboon-like ape (Cynopithecus nigrescens), an antelopean buffalo (Anoa depressicornis), and the babyroussa (Babirusa alfurus). Several of these, or closely allied forms, are also found in the Moluccas, and in the group of islands and islets which stretch eastward from Lombok to Timor. We have here, in addition, one of the commonest species of Malay monkey, the Macacus cynomol- gus, a Paradoxurus, and a possible second species of deer, Cervus Timoriensis. The implacental mammals of the connecting region comprise only Cuscus and Belideus. , V. = Distribution of marine life.—Nature of the deep-sea fauna.—Oceanic pelagic tauna.— Littoral fauna.—Pelagic faunas of lakes.—Deep-lake faunas. DISTRIBUTION OF MARINE LIFE. One of the most important results of deep-sea explorations is the establishment of the fact that the distribution of oceanic life has no depth-limit. Contrary to the opinion so long entertained by naturalists that this life was confined to a shallow zone, extend- ing but a few hundred feet beneath the water's surface, it is now known that representatives of all the marine invertebrate classes, and probably also fishes, exist at the greatest depths that have been reached by the dredge, and that in all likelihood a fair proportion of these penetrate even to the profounder abysses of four or five miles. The most extensive organic deposits accumulating in the trough of the sea are made by the Radiolaria and Foraminifera, whose world- wide distribution and prodigious development give the determining character to the oceanic floor. The well-known “ Globigerina,” or “ Atlantic” ooze, 4 composition in principal part of the calcareous tests of four or five genera of Foraminifera (Globigerina, Orbulina, Spheroidina), constitutes the bed of the sea at nearly all points be- tween the depths of four hundred and two thousand, or two thou- sand five hundred fathoms, except where, as in the immediate neighbourhood of coast-lines, the bottom is formed by the conti- nental debris. Over this vast calcareous area animal life is far more abundant than over the comparatively sterile region where, for any reason, the ooze is wanting, and where, consequently, there is a marked deficiency in the material necessary for the proper develop- ment of many of the lower forms of life. Thus, it has been noticed that in such localities chiefly the shell-less orders of animals, as the Holothuroidea and the Annelida, are represented. Beyond a depth 110 GEOGRAPHICAL DISTRIBUTION. of some two thousand five hundred fathoms shell accumulations almost completely cease, their place being taken by a “ red-clay” deposit, whose exact nature is, perhaps, not yet clearly understood. The absence of foraminiferal tests from the areas of greatest depth is doubtless due to the dissolution of the calcareous matter of the shell during its descent from the surface to the bottom, most of the pelagic forms, there is good reason to believe, being restricted in their range to a superficial zone of a few hundred fathoms depth. The sponges, although they attain a maximum development in a zone of five hundred to one thousand fathoms, extend to the greatest measured depths, and are represented in the deepest parts by all the recognised orders, with the exception of the Calcarea (calcareous sponges), which appear to be confined to shallow water. The Hexactinellide, among siliceous sponges, to which the ‘“ glass- rope sponge” (Hyalonema) and Venus’ flower-basket (Euplectella) belong, and whose earliest representatives appear already in the fauna of the Cambrian period, preponderate in the abyssal regions. The ordinary horny sponges (Keratosa), while they possess a very considerable vertical range, have their special development in the coralline zone. In the deepest parts of the sea corals are but spar- ingly distributed, and by far the greater number of species belong to the type of simple corals, and to the family Turbinolida, a large proportion of the genera passing back to the Tertiary period, and a few to the Cretaceous. No true Paleozoic forms have as yet been discovered. But five genera of Madreporaria are known whose range extends to, or exceeds, fifteen hundred fathoms (nine thou- sand feet), and only a single one, Bathyactis, which transgresses the twenty-five hundred fathom line. The vertical range of some of the species is very extraordinary, most notably so in the case of Bathyactis symmetrica, which is found in all depths between thirty (Bermuda) and twenty-nine hundred fathoms (east of Japan).°° Several species of Meduse have been obtained from depths re- ported to exceed two thousand fathoms; but it is, perhaps, open to question whether some, or even most, of these apparently deep- sea forms are not in reality inhabitants of a comparatively shallow superficial zone, and have not been simply caught in the hauling of the net. There appears to be strong evidence, however, for con- cluding that at least a few of the forms are actually inhabitants of deep water. DEEP-SEA FAUNA. 111 Among the deep-sea Echinodermata there are representatives of all the modern orders—crinoids, brittle-stars, star-fishes, urchins, and holothurians—but none of the ancient palechinoids, cystids, or blastoids are known. The pear-encrinites (Apiocrinida), for a long time supposed to have become extinct with the Mesozoic era, con- tinue their succession in the genera Rhizocrinus, Bathycrinus, and Hyocrinus, forms more strictly abyssal in character than the Penta- crinus, whose greatest development seems to be confined to a zone of a few hundred fathoms. Bathycrinus gracilis has been dredged in water of a depth of two thousand four hundred and thirty - five fathoms. ** The Asteroidea (star-fishes) and Ophiuroide (brittle-stars) are diffused throughout all the oceanic zones that have thus far been dredged, the former abounding more particularly at moderate depths. The singularly aberrant, and universally distributed, genus of star-fishes, Brisinga, is one of the commonest and most distinct- ive forms of the abyssal fauna, being found in all depths from four hundred to three thousand fathoms. Of the brittle-stars, of which there are about five hundred species described, more than two hun- dred are restricted in their range to a zone of thirty fathoms. De- spite this apparent localisation of the species to a shallow belt, there are no less than sixty-nine species which descend below one thou- sand fathoms, and about eighteen below two thousand. None of the genera have been positively identified with fossil forms, although not unlikely the Jurassic Ophioderma may in part belong to Ophiura or Pectinura, The affinities of the Triassic Aspidura are still doubt- ful.*7 The relationship existing between the modern echinoid fauna and the faunas of past geological periods is much more marked; indeed, this relationship may be considered as one of the most dis- tinctive features of the deep-sea fauna. Not only do a considerable number of the living genera date back to the Cretaceous period, but a fair proportion of those of the families Cidaride, Echinida, Salenide, &c., are already found in the deposits of the Jura, the Lias, and even in the Trias. The Tertiary genera are very largely developed, and the utmost similarity prevails, even among the spe- cies. So close is the identity existing between the West Indian urchins and those occurring fossil in many of the European Tertiary beds (older and median Tertiary), that it becomes practically im- possible, or nearly so, to distinguish between the species. This 112 GEOGRAPHICAL DISTRIBUTION. correspondence manifests itself among both the regular and irregu- lar forms. In their bathymetrical distribution the echinoids appear to be governed by much the same conditions as have been observed in the case of the brittle-stars. By far the greater number of spe- cies—about two hundred—are of a littoral habit, occupying the belt of one hundred to one hundred and fifty fathoms, although not a few of them, like Echinocardium Australe, which descends to two thousand six hundred and seventy-five fathoms, penetrate deep into the abyssal zone. The number of continental species, or such whose normal habitat is included approximately between the one hundred to one hundred and fifty and the five hundred fathom line is forty-six, and a slightly larger number, fifty, may be considered to be strictly abyssal. The species passing below two thousand fathoms are rather limited, and only one is known—Pourtalesia laguncula—whose range embraces the twenty-nine hundred fathom line. This form is also found in the continental belt.* The sea-cucumbers, or holothurians, which are very generally distributed throughout the oceanic abyss, constitute one of the most distinctive elements of the deep-sea fauna. As has already been seen, they, together with certain annelids, form a large part of the fauna of the ‘‘red clay,” or of the region which lies beyond the reach of foraminiferal shells. Deep-sea crustaceans are very abundant, and many of them are remarkable for their colossal size, their bizarre forms (Nematocar- cinus gracilipes), and brilliant red coloring. Partaking of the first character are the giant blood-red shrimps of the genus Aristzus, and several members of the order Schizopoda. A Gnathophausia was obtained off the Azores, by the officers of the ‘ Talisman,” measuring no less than twenty-five centimetres (nearly ten inches) in length. The peneid and caridid shrimps, among the long-tailed decapods, are strikingly numerous, and present many very singular forms. It would seem, from the observations of the ‘‘ Challenger,” that the Brachyura, or crabs, were confined almost entirely to com- paratively shallow water, although at depths of one thousand to fifteen hundred fathoms they appear to have yielded a sufficient harvest to the naturalists of the French expedition. Hermit-crabs were collected by the ‘‘ Talisman ” in water of from four thousand to five thousand metres.‘ Many of the pedunculated barnacles are of uncommonly large size, surpassing in this respect the shallow-water DEEP-SEA FAUNA. 113 forms. As might have been expected from our knowledge of cave- faunas, and the habits of those animals, there are a number of blind crustaceans inhabiting the deep, as Nephropses, Polycheles, &c., the last in a manner representing the Jurassic Eryon. Many of the species, on the other hand, are profusely phosphorescent. Neither of the three more important orders of mollusks, the Lamellibranchiata, Gasteropoda, or Cephalopoda, enter very largely as components of the deep-sea fauna, although of the first two scat- tered individuals are not exactly uncommon at nearly the greatest depths. Leda and Arca were obtained from a depth of 16,000 feet. The Cephalopoda are the least numerous, and not unlikely the majority of the apparently deep-water forms represent in reality only captures from shallow water. Wyville Thomson has called attention to the remarkable fact that only on one occasion did the officers of the “ Challenger” take the animal of Spirula, ‘although the delicate little white coiled shell is one of the commonest objects on the beach throughout the tropics—sometimes washed up in a long white line, which can be seen from any distance.”*' The Brachiopoda, while enjoying a very broad geographical distribu- tion, are by no means numerous, either specifically or numerically. Although seemingly on the verge of extinction, it would appear as though the actual specific diminution since the beginning or middle of the Tertiary period has not been very great. Most of the recent species are technically shallow-water forms, by far the greater num- ber being found above the five hundred fathom line. Ten species range to depths of six thousand feet and over, and one, Terebratula Wyvillei, was dredged in twenty-nine hundred fathoms. Al! depths have furnished specimens of Polyzoa. Our knowledge respecting the bathymetrical distribution of the deep-sea fishes, owing to the difficulty of determining whether the specimens hauled by the net have been actually taken in the depths indicated by the sounding-line, or have been simply captured dur- ing the ascent of the net, is not very precise, and barely sufficient to permit of any general conclusions being drawn froni it. That fishes abound at very great depths there can be no question; but whether they are equally distributed in the great zone lying be- tween the surface and bottom waters, may still be considered doubtful. The researches of the ‘‘ Challenger” would seem to in- dicate that this intermediate area is largely, if not almost wholly, 9 114 GEOGRAPHICAL DISTRIBUTION. destitute of such forms, whereas the evidence brought by the “Talisman” tends in just the opposite direction. Thus, in one haul taken off the Cape Verde Islands, in four hundred and fifty metres water, the net brought up no less than one thousand and thirty-one fishes, mostly belonging to the genus Melanocephalus. At depths of one thousand to one thousand five hundred metres in the North African Atlantic, they are stated by Milne-Edwards to abound, and on the bank lying some one hundred and twenty miles off Cape Nun, where in water of from two thousand to two thousand and three hundred metres M. Vaillant obtained the singular Eury- pharinx pelecanoides, they are still very varied. Many of the species possess an extraordinary vertical range, accommodating themselves apparently with ease to the most varied conditions of pressure. Alepocephalus rostratus is met with in a zone included between nine hundred and three thousand six hundred and fifty metres, and much the same distribution characterises Scopelus Madcrensis. Macrurus affinis is found between five hundred and ninety and two thousand two hundred metres. The greatest depth from which any fish has been obtained is about five thousand metres (Bathyopis ferox).** The deep-sea fishes, although frequently characterised by many very remarkable abnormalities of structure, such as the enormous development of the head or jaw, the ribbon-like body, and the possession of phosphorescent organs, do not belong to any peculiar order, and are in the main simply modified forms of surface types. A large proportion of the species belong to the families Ophidiida, Scopelide, and Macruride. In summing up the results obtained from a first general survey of the collections obtained by the ‘ Challenger,” Sir Wyville Thomson believes that we are warranted in arriving at the follow- ing general conclusions : “* ‘1, Animal life is present on the bottom of the ocean at all depths. “¢2, Animal life is not nearly so abundant at extreme, as it is at moderate depths; but, as well-developed members of all the marine invertebrate classes occur at all depths, this appears to de- pend more upon certain causes affecting the composition of the bottom deposits, and of the bottom water involving the supply of DEEP-SEA FAUNA. 115 oxygen, and of carbonate of lime, phosphate of lime, and other materials necessary for their development, than upon any of the conditions immediately connected with depth. “3. There is every reason to believe that the fauna of deep water is confined principally to two belts, one at and near the sur- face, and the other on and near the bottom; leaving an intermediate zone in which the larger animal forms, vertebrate and invertebrate, are nearly or entirely absent. “A, Although all the principal invertebrate groups are repre- sented in the abyssal fauna, the relative proportion in which they occur is peculiar. Thus Mollusca in all their classes, brachyurous Crustacea, and Annelida, are on the whole scarce; while Echino- dermata and Porifera greatly preponderate. “<5. Depths beyond five hundred fathoms are inhabited through- out the world by a fauna which presents generally the same features throughout; deep-sea genera have usually a cosmopolitan extension, while species are either universally distributed, or, if they differ in remote localities, they are markedly representative; that is to say, they bear to one another a close genetic relation. “6, The abyssal fauna is certainly more nearly related than the fauna of shallower water to the faunw of the Tertiary and Sec- ondary periods, although this relation is not so close as we were at first inclined to expect, and only a comparatively small num- ber of types supposed to have become extinct have yet been dis- covered. “6”, The most characteristic abyssal forms, and those which are most nearly related to extinct types, seem to occur in greatest abundance and of largest size in the Southern Ocean; and the gen- eral character of the fauna of the Atlantic and of the Pacific gives the impression that the migration of species has taken place in a northerly direction, that is to say, in a direction corresponding with the movement of the cold undercurrent. ‘«8, The general character of the abyssal fauna resembles most that of the shallower water of high northern and southern latitudes, no doubt because the conditions of temperature, on which the dis- tribution of animals mainly depénds, are nearly similar.” (‘‘ The Atlantic,” IT.) Nature of the Deep-Sea Fauna.—Much diversity of opinion exists among naturalists as to the nature of the deep-sea fauna, 116 GEOGRAPHICAL DISTRIBUTION. That it is not one governed by conditions of temperature alone, or in principal part, as has very generally been conceived, is made manifest by an examination of the bathymetric distribution which particular animal groups affect. Thus, the reef-building corals, which for their proper development require an average tempera- ture of 70° to 75° Fahr., and a temperature never falling below 68° Fahr., are confined to a superficial zone of twenty fathoms; yet at most parts of the oceanic surface inhabited by these animals a suitable temperature would be found at depths fully five times as great, and in some quarters even very much greater. Over the tropical Pacific, for example, a temperature of 77° Fahr. prevails to a depth of eighty fathoms, and of 70° Fahr. down to one hundred fathoms, so that, as far as temperature alone is concerned, the coral animal might just as well have found a congenial home in those greater depths as in the shallower one of ten to twenty fath- oms. Indeed, in the Red Sea the coral isotherm would still be found at the very bottom, or in a depth of water of six hundred fathoms; but here, as elsewhere, the limiting line is found at twenty fathoms. With reference to the vertical distribution of these ani- mals, therefore, the matter of temperature would seem to be but little involved. What is true of the corals doubtless applies .in considerable part to many other animal groups; but it must be confessed that our knowledge respecting the thermal conditions necessary for the existence of most marine organisms is so limited that we can hardly premise at the present day upon any safe deduction being based upon it. Professor Fuchs ** has quite recently emphasised the fact, however, as tending to prove the non-influence of temperature in determining distribution, that over the entire world almost all the important types of the deep-sea fauna are already represented at the comparatively insignificant depth of ninety to one hundred fathoms, and consequently inhabit a zone the extremes of whose av- erage temperature may be separated by fully thirty to forty degrees. Thus, it is pointed out that on the Pourtales Plateau, off the coast of Florida, which begins at ninety fathoms, and descends to three hundred fathoms without showing any essential modification in its inhabiting fauna, deep-sea forms are very plentiful, especially corals, siliceous sponges, and echinoderms; and the same is the case with the famous Barbadoes grounds. A well-marked deep-sea fauna has DEEP-SEA FAUNA. 117 long been recognised in the Atlantic and Mediterranean waters of Europe as occupying the one hundred fathom zone; and it has been equally observed along the coast of Brazil, the Philippines, and elsewhere. The fact that almost everywhere this upper limit of faunal distribution should correspond with a line of nearly uniform depth is certainly very remarkable, and one that argues strongly against the nétion of thermal influences. For, if the determining factor in vertical distribution were really the matter of temperature, we should naturally expect to find the defining line between the surface and deep-sea faunas to be differently located for different parts of the earth’s surface, rising in the polar and high temperate regions, where the surface temperature of the water is itself very low, and falling in the region of the tropics, whereas, as a matter of fact, no such condition obtains. Indeed, on the principle gen- erally entertained, there ought to be in the high northern and southern latitudes no such thing as an abyssal fauna, inasmuch as the thermal conditions requisite for its existence would be those corresponding to the surface fauna as well, a nearly uniform tem- perature extending through the sea from top to bottom. We should then expect to meet with the characteristic deep-sea forms of corals, brachiopods, vitreous sponges, echinoderms, &c., seemingly indica- tive of a low temperature, in the littoral region, but, as is well known, they do not occur there, although they are sufficiently abundant in deep water. It is true that certain animals occuring in the deeper parts of the warm seas are known as surface forms only in the Arctic waters; but these are inconsiderable in number, and in the main uncharacteristic, so that they can scarcely be con- sidered as a link uniting the littoral with the deep-sea faunas; in a general way the two are as sharply defined in the Arctic Seas as anywhere else. But, if it is not the matter of temperature that is principally involved in the formation of a deep-sea fauna, what is ? The question does not, perhaps, at the present moment admit of a definite solution; but.a suggestion thrown out in this direction by Professor Fuchs deserves careful attention. After reviewing the possibilities that may arise from such proximate causes as diflerences in the chemical characters of the water, the quantity of absorbed air contained in it, and currental motion, all of which must assuredly be of insignificant import, this eminent authority arrives at the con- clusion that the only factor which can, in any material way, affect 118 GEOGRAPHICAL DISTRIBUTION. vertical distribution is light. It is claimed in confirmation of this view that the limit of light-penetration in the oceanic waters, as fixed by Secchi, Pourtalés, and Bouguer, corresponds closely with the forty to fifty fathom line, marking the upper boundary of the deep- sea fauna, or, more strictly, the line separating the littoral from the deep-sea fauna. Below this line, therefore, the fauna is one of dark- ness, and above it, except in so far as certain animal groups may be nocturnal in their habits, one of light. In support of this proposi- tion Professor Fuchs emphasises the fact that, ‘‘ with their character of animals of darkness, numerous peculiarities in the organisation and nature of the deep-sea animals agree. Thus it is known that very many deep-sea animals either have uncommonly large eyes, after the fashion of nocturnal animals, or are completely blind; it is also well known that they are, for the most part, either pale and colour- less, or unicolourous, and that varied colouration is exceedingly sel- dom met with among them; and, finally, it is likewise well known that a very large proportion of deep-sea animals, in many groups, indeed the majority, are vividly luminous. This last peculiarity is of special importance, for it is clear that luminosity can be of con- sequence only to such animals as are destined to live in darkness, and, in point of fact, scarcely any luminous animals are known to us from the littoral region.” While it may, perhaps, be admitted that temperature is not the only, or even principal, agent in determining distribution, it must, nevertheless, be confessed that certain grave objections present themselves to the theory which looks upon light as the determin- ing factor; indeed, the objections are much of the same kind as those which have been urged against the thermal theory. If the fact is surprising that corals do not descend below the one hundred and twenty foot line, when the temperature for a very considerable distance beyond that point is still above the normal required by them, is it not perhaps equally surprising that they should be limited at this point at all, seeing that the penetration of light ex- tends to fully double or treble the depth, or, as has been more re- cently shown by MM. Fol and Sarasin in the case of the Mediterra- nean Sea, to even ten times that depth? Can it be rationally conceived that such lowly organisms, devoid of special visual or- gans, can be so affected by the conditions of light and darkness as not to be able to endure that amount of obscurity which distin- PELAGIC FAUNA. 119 guishes the zone immediately underlying the twenty fathom line ? This scarcely appears possible. The extended range of a very large proportion of the animal forms entering into the composition of the littoral fauna, and the extreme rarity of instances in which limitation is so marked as to render most effective the difference between light and darkness, argue strongly against the notion of the all- paramount influence of light as affecting distribution. This objection to the views advanced by Professor Fuchs, as opposed to the doctrine of thermal limitation, is further strengthened by the fact which has been noted in the case of many animal groups (e. g., the Brachiopoda) that the vertical range of surface forms is on an average greater in the boreal and hyperboreal regions—i. e¢., where the temperature of the water is more nearly uniform—than in the more centrally located regions, where a much broader variation in the temperature of the water manifests itself. It is true, as has been urged by Professor Fuchs, that the littoral fauna is largely dependent for its development upon the existence of coral reefs and coast-binding shell-banks; but in how far this association is connected with the presence or absence of light, still remains to be determined. On the whole, while it may be assumed that we are still largely ignorant of the fundamental facts underlying dis- tribution, it appears more than likely that not a single cause, but a combination of causes, is operative in bringing about the general result. That the deep-sea fauna is a fauna of darkness must be admitted; but this is so from the necessity of the case rather than a matter of choice resting with the animals composing it. A singular correspondence has been noted as existing between the pelagic (surface) oceanic fauna and the fauna of the oceanic bottom (abyssal)—a correspondence that has likewise been attrib- uted by some to a condition of darkness by which the different organisms are supposed to be governed. To what exact degree the members of this animal assemblage are nocturnal in their habits, or constitute true animals of darkness, the observations are not suffi- ciently far advanced to permit of a general conclusion being ar- rived at. Pelagic Fauna.—Under the designation ‘‘ pelagic” may be in- cluded those forms of life which habitually pass their existence on the free expanse of the ocean, and which only on accidental occa- sions, if at all, visit the continental borders, or descend to the floor 120 GEOGRAPHICAL DISTRIBUTION. of the sea. Such are the radiolarians, certain foraminifers and in- fusorians, the siphonophorous meduse (Portuguese man-of-war, Physalia; Velella, Porpita), winged-shells (pteropods), a limited number of gasteropods (Atlanta, Ianthina, Glaucus, &c.), cephalo- pods, and tunicates (Salpa, Pyrosoma). The schizopod and ento- mostracous Crustacea are numerously represented, while a genus of hemipterous insect (Halobates) finds a suitable home clinging to the waves at practically all distances from the land. A number of fishes, ‘such as the herrings, mackerel, tunny, swordfish, flying-fish (Exoceetus), flying-gurnard (Dactyloptera), sea-horse, and most of the sharks, some of which approach the shore during the spawning season, might be added to this list, and among the Mammalia the whales and dolphins. The primary condition governing the existence of a pelagic fauna is manifestly the development over the oceanic expanse of vegetable life. This is found, for the most part, in the microscopic diatoms and the Oscillatoris, the former of which abound more particularly in high northern and southern latitudes, frequently, by their vast numbers, rendering the water thick as soup, and impart- ing to it a peculiar brownish or blackish tint, the so-called ‘“ black water” of Arctic navigators. In the temperate and warmer seas the diatoms are largely replaced by the oscillatorians, whose profuse development is no less remarkable. In the Arafura Sea, between Australia and New Guinea, the officers of the ‘‘ Challenger” found the water continuously discoloured during a period of several days’ sail, and giving out the odour of a reedy pond; and in the Atlantic they ‘‘ passed for days through water full of minute alge: (Tricho- desmium), gleaming in the water like particles of mica.” * It is to a species of Trichodesmium (T. erythreum) that is due the peculiar red colouring frequently seen over stretches of the Red Sea. Were it not for this profuse vegetable growth the sea would probably be, in great part, an uninhabited waste. The alge fur- nish the necessary nutriment to the simpler forms of animal life, which in turn yield their substances to those more highly organised. In this manner a true interdependence of conditions, or balance of life, is maintained. Professor Moseley, however, believes that in some parts of the ocean the quantity of freely suspended vegetable * Moseley, ‘‘ Nature,” xxvi., p. 559, PELAGIC FAUNA. 121 growth is not sufficient to maintain the animal life which appears to be nourished by it, and he suggests that the deficiency may be made good through a peculiar symbiotic relation which appears to exist between certain lowly-organised plants and animals. Thus, many of the radiolarians and comb-bearers (Ctenophora) contain, embedded in their body-substance, a number of yellow starch-cells, which Brandt recognises as unicellular alge (Zooxanthelle), and which are supposed to thrive upon the waste products of the ani- mal, and to yield to it in turn the compounds elaborated in the process of its own development. The relation of mutual benefit which is here stated to exist probably requires further investigation before it can be accepted as an absolute fact.* One of the distinctive characters of the majority of pelagic ani- mals is their transparency, which renders them very nearly invisible on the surface of the water. The nerves, muscles, skin, and organs generally, are alike hyaline, although in many instances the liver has remained unaffected. The protection thus afforded to such animals as the radiolarians, jelly-fishes, tunicates, and many crus- taceans, is compensated for in animals less transparent by a colour- ing which harmonises with that of the open sea. Thus, the pre- dominating colour is either blue or violet, as we find it in the Portuguese man-of-war, the Velella and Porpita, and in Ianthina and Glaucus among the snails. The fishes are principally steel-blue above and lustrous white underneath, a want of correspondence which is also manifest in other animal groups. Glaucus, just men- tioned, whose progression is effected in the manner of the common pond-snail, ventral surface uppermost, has this side coloured blue, and the opposite, or dorsal side, silver-white. Exceptional cases are presented of an extreme brilliancy of colour, as in the copepod Sapphirhina, which is said to rival in metallic lustre the humming- birds, and to display the colours of the spectrum with the intensity of the gleam of the diamond. *° Most of the pelagic animals, except the lowest, are devoid of a shell, or, when present, the shell is usually very thin and fragile, * Professor Hensen estimates that in some parts of the Baltic there are upwards of 140,000,000 plants (Rhizosolenia, Cheetoccros) in every ten cubic metres of water, ard maintains that this prodigious quantity is produced in the course of about two months. ‘ Bulletin of the United States Fish Com- mission,’? August, 1885. 122 GEOGRAPHICAL DISTRIBUTION. as in Argonauta, Cleodora, Atlanta, Carinaria, Ianthina, &c. Ab- normalities of structure, especially in the case of the immature forms of littoral species, are frequent, leading to such modification of out- line as to obscure in great measure the general parental relationship. The supposed young of the conger-eel develop into small transpar- ent ribbon-shaped fishes, largely devoid of hemoglobin in their blood, and with an exclusively cartilaginous skeleton; the young of certain flat-fishes (Platessa) die without ever reaching maturity, and before the eyes have become asymmetrically placed; and, in the case of some of the rock-lobsters (Palinurus), the flattened larvee attain to gigantic proportions, Other instances of such abnormal development might be mentioned. The unusually large size of the eyes in some of the annelids and crustaceans (Alciops, Corycseus) recalls a similar characteristic belonging to many of the deep-sea forms of life; likewise the total absence, or very rudimentary con- dition (as in pteropods), of these organs. The power of emitting phosphorescent light is another feature held in common by many of the surface forms of life with the fauna of the deep. Pyrocystis and Noctiluca, amceboid bodies on the border-line between the Foraminifera and Infusoria, appear to be the principal contributors to the general oceanic phosphorescence. A remarkable feature of the pelagic fauna is the vast swarms or schools in which many of the forms are‘found, association being the rule rather than the exception, and the broad expanse over which the greater number of the types are spread. The genera are of almost universal distribution, and many even of the species, of both the higher forms (fishes) and the lowest, are identical over the most distantly removed quarters of the globe; the polar faunas, however, which are constituted. principally by the crustaceans, pteropods, and whales, differ materially from the faunas of the temperate and equatorial belts, lacking largely in the meduse, the tunicates, and pelagic fishes. The varying salinity of the oceanic waters appears very sensibly to affect this fauna, whose distribution is, accordingly, in a measure governed by it. Thus, the surface-fauna of the Baltic is very meagre, and in the upper part of the basin, where the waters are nearly fresh, it is reduced to little more than a very limited number of crustaceans. Some of the medusoids, however, as Aurelia and Cyanea, appear to be but little affected by a deficiency in the salt-supply, and, indeed, PELAGIC FAUNA. 123 according to Moseley, they would seem to prefer a habitation near the mouths of fresh-water streams, being seen to crowd up towards the heads of fjords and inlets. In the Hawkesbury inlet, New South Wales, the Scyphomeduse were observed by this naturalist swimming in shoals where the water was so pure as to be quite drinkable. Much uncertainty still exists as to the relation which the free oceanic fauna bears to the fauna of the deep-sea, an uncertainty due to the difficulty of determining the actual depth whence the different organisms caught in the net were obtained. Alexander Agassiz maintains, as the result of experiments made with the Sigsbee net, the most improved appliance thus far invented for the purposes of deep-sea exploration, that “the surface-fauna of the sea is really limited to a comparatively narrow belt in depth [about fifty fathoms], and that there is no intermediate belt, so to speak, of animal life between those animals living on the bottom or close to it, and the surface pelagic fauna.” *’ Beyond a depth of one hundred fathoms nothing was found. On the other hand, the numerous observations made by Mr. Murray on board the “Challenger,” with appliances less perfect than those used by Mr. Agassiz, almost conclusively prove that the depth penetration is very much greater than is here indicated, and that possibly a direct continuation exists in the case of certain groups of animals between the pelagic and abyssal faunas. The fact seems to be pretty satisfactorily established, however, that the true zone of free oceanic life, or that which is most numerously inhabited, is a shallow one, and that whatever life extends to great depths is comparatively restricted. It would appear that a large proportion, if not the greater num- ber, of the pelagic animals are more or Jess nocturnal in their habits, shunning the glare of daylight, and appearing on the actual surface only during the hours of evening and night. Such are most of the pelagic fishes, crustaceans, pteropods, heteropods, and fora- minifers, which in their hidden depths for a long time eluded the search of naturalists. The radiolarians, jelly-fishes, and certain crustaceans, on the other hand, seem to prefer the open daylight, appearing at all hours on the surface during calms; and the same is the case with a number of fishes, as the flying-fish and dolphin (Coryphsena). There is thus a perpetual oscillation in this upper 124 GEOGRAPHICAL DISTRIBUTION. zone of life, which, as dependent upon an excess or deficiency in illumination, probably does not extend much beyond a depth of fifty fathoms. There can be but little doubt that a pelagic fauna antedated all the faunas of the globe, and that from it, through a long process of modification and adaptation, have been derived the faunas of the shore, the abyssal deep, the land-surface, and the various fresh- -waters. The identity, or close resemblance, existing between the larval forms of many of the most divergent animal groups clearly indicates the lines along which modification has resulted, for it can scarcely be conceived, as Professor Moseley well insists, that this general identity in larval structure could have been brought about as the result of natural selection after the adult forms had largely diverged from one another. The earliest traces of a pelagic fauna are indicated in the rocks of Cambrian age, where, as representative of it, we find, besides the remains of pteropods, the impressions of jelly-fishes, which were apparently not very far removed from some modern Scyphomeduse. The marine animals that are deficient or lacking in the composition of the pelagic fauna, and not improbably have always been lacking, are the sponges, alcyonarian corals, sipunculoid worms, brachiopods, lamellibranchs, and echinoderms. The true infusorians (Ciliata) appear to be but very feebly repre- sented, although there is an abundance of the Cilioflagellata. Nature of the Littoral Fauna.—That the littoral fauna is either wholly or in great part a derivative of the free oceanic or pelagic fauna there is every reason to believe. The supposition that the latter came into existence before the former is at once a natural one, and is supported, apart from general zoogeological considerations, by the character of the mutually related littoral larvee, whose adaptation to a pelagic existence clearly indicates the nature of their primal condition. There is, further, every reason to believe that the earliest plants were also largely pelagic, and that not until these had firmly established themselves as permanent forms along the sea-border was there developed a shore-fauna. In exposing themselves to the manifold conditions, such as the break- ing of the surf, tidal action, shore-wash, attacks of enemies, which a change of abode entailed upon the members of the pelagic fauna, these were by force of adaptation compelled to undergo par- ticular modifications of habit and structure which rendered them LITTORAL FAUNA. 125 better fitted to their new surroundings. This we see in the defen- sive armour or encasement with which a very large number of the shore animals are provided, a character which eminently distin- guishes them from the inhabitants of the open ocean. The shells, which are with the latter in most cases very thin and fragile, as in Atlanta, the argonaut, and the pteropods generally, are in the vast majority of shore animals thick and resisting, and capable of with- standing the numerous strains and impacts to which they are sub- jected. , But the same causes which have been operative in producing modifications in the pelagic fauna have been influential in bringing about a no less important series of modifications in the littoral fauna as well. The intermingling of fresh and salt waters about the embouchures of rivers, or a deficiency, as in the ice-bound north, in the salinity of the sea itself, will have gradually paved the way for the formation or evolution of animal forms destined to live eventually in fresh water. Hence, the origin in principal part of the fresh-water faunas. Similarly, frequent exposure to the at- mosphere beyond the interacting influence of the aqueous medium, as in the region of ‘‘ between tides,” will have developed a method of respiration, or respiratory apparatus, other than that which is dependent for its action upon the presence of water. The remark- able series of modifications which the Amphibia (frogs, toads, sala- manders) undergo from their larval condition, when, as inhabitants of the water, they breathe by gills, to their adult stage, when respiration is in most cases effected through the intermedium of lungs alone, most forcibly illustrate the progression which, at least in one division of the animal series, the vertebrates, has led to the formation of the air-breathing or terrestrial fauna. But other instances of adaptation from an aqueous to a terrestrial existence are not wanting. Many fishes have their gills so modified as to permit of a very protracted existence on dry land, while, as is well known, the lung-fishes (Dipnoi) have developed true lungs. Land-crabs are very abundant in the Tropics, roaming about in the interior at very considerable distances from the shore. In Japan they have been observed at an elevation of four thousand feet above the sea. The remarkable cocoanut crab, Birgus latro, is provided with a pair of true lungs, developed on the walls of its gill cavities. Professor Moseley ** thus sums up the relations of the littoral 126 GEOGRAPHICAL DISTRIBUTION. fauna: “The fauna of the coast has not only given origin to the terrestrial and fresh-water faunas, it has throughout all time, since life originated, given additions to the pelagic fauna in return for having received from it its starting-point. It has also received some of these pelagic forms back again to assume a fresh littoral existence. The terrestrial fauna has returned some forms to the shores, such as certain shore-birds, seals, and the polar bear; and some of these, such as the whales and a small oceanic insect, Halo- bates, have returned thence to pelagic life. “The deep-sea fauna has probably been formed almost entirely from the littoral, not in most remote antiquity, but only after food, derived from the débris of the littoral and terrestrial faunas and floras, became abundant in deep water. It was in the littoral region that all the primary branches of the zoological family-tree were formed; all terrestrial and deep-sea forms have passed through a littoral phase, and amongst the representatives of the littoral fauna the recapitulative history, in the form of series of larval conditions, is most completely retained.” : Lake Faunas,—It would appear that in all large lakes three distinct faunas can be recognised: 1. The littoral fauna, comprising the animals of the shore-line, which do not habitually descend to a much greater depth than fifteen or twenty feet. 2. The deep fauna, whose representatives live along the floor of the lake, at depths usually exceeding sixty to a hundred feet, a limited number of forms occasionally rising to the surface; and 3. The pelagic fauna, whose members occupy the free surface of the lakes, rarely or never _ reaching the shore-line or descending to the bottom. The zone inhabited by the last measures from fifty to a hundred metres in depth. Our general knowledge respecting the pelagic fauna is still very limited, and is based almost exclusively upon observations made upon the European lakes. From these it would seem that the fauna is a very restricted one, consisting, as far as is known, of some twenty-five species of entomostracous crustaceans (ostracods, cladoceres, and copepods), a fresh-water mite (Atax crassipes), about six species of rotifers, and a limited number of infusorians. No lake has thus far yielded all these forms, and the majority of lakes are largely deficient. Between the years 1874 and 1878 Forel * ob- tained in the Lake of Geneva only eight species: Diaptomus castor, LAKE FAUNAS. 127 _ Cyclops (sp. undet.), Daphnia hyalina, D. mucronata, Bosmia lon- gispina, Sida crystallina, Bythotrephes longimanus, Leptodora hya- lina. Of the total number of twenty-four species which were ob- tained by Pavesi® from the Italian lakes. belonging almost exclu- sively to such genera as occur in Lake Geneva, only four (Daphnia hyalina, D. galeata, Bosmia longispina, Leptodora hyalina) are known to inhabit the Lago Maggiore, and an equal number the Lago diComo. The Lago d’Iseo, on the other hand, has ten spe- cies, and Orta and Mergozzo eleven each. As far as the Crustacea are concerned, the Swiss lakes appear to be less rich in point of species than the Scandinavian; but they alone, with the adjoining lakes of Annecy and Bourget, in Savoy, have thus far yielded any variety of forms of lower organisation than the articulates. M. Imhof’s investigations have brought to light, as constituents of the Swiss pelagic faunas, two species each of flagellate (Dinobryon) and cilioflagellate (Peridinium, Ceratium) infusorians, two species of true infusorians (Epistylis lacustris, Acineta elegans), which live attached on the crustaceans, and the six rotifers already referred to, belonging to the genera Conochilus, Asphanema, Anureea, Triarthra, and Polyarthra. Doubtless some of these forms will also be found in the more northern and southern lakes.* The general characters common to the animals of the pelagic region, which are the outcome of their particular mode of life, are thus briefly summarised by Forel: ‘‘ They must swim incessantly, without ever being able to rest upon a solid body, and, instead of any organ of adhesion, they possess a highly developed natatory apparatus; their specific gravity, which is nearly the same as that of the water, enables them to swim about in the water without any great muscular exertion. They are rather sluggish animals, and escape the enemies that pursue them rather by their transparency than by their activity; they are, indeed (and this is their character- istic peculiarity), perfectly transparent, like crystals; and only their strongly pigmented black, brown, or red eye appears distinctly. This nearly perfect transparency of the pelagic animals may be re- garded as a mimicry acquired by natural selection; only the animals *¢ Ann, and Mag. Nat. Hist.,’? December, 1883; January, 1884. Since the above was written Imhof has identified several of the Swiss crustaceans, rotifers, &c., in the lakes of Alsace-Lorraine. ‘ Zoologisher Auzeiger,’’ De- eember, 1885.5 128 GEOGRAPHICAL DISTRIBUTION. which are as transparent as the medium in which they live have held their own.” The lacustrine pelagic animals perform daily vertical migrations of the same character as has been noted in the case of the oceanic pelagic fauna, descending to the regions of obscurity during the day-time, and ascending by night. The animals appear to shun the light of the sun, and even of the moon, and hence retire to a depth probably not far from the limits of light penetration; the fauna is, therefore, one of darkness. The greatest depth whence specimens were obtained by Forel in Lake Geneva was about one hundred and fifty metres; but at this depth only Diaptomus was found. At a depth of fifty metres, in the Lago d’Orta, Pavesi found a very profuse fauna, represented by seven species; in the Lago d’Iseo, at five, fifteen, and thirty metres, the catch appears to have been exceedingly abundant (‘‘la pesca fu prodigiosamente ab- bondante”); but, at one hundred metres, where the temperature of the water was 19° C., as compared with a surface temperature of 23° C,, the fauna was decidedly scanty, although five distinct forms were obtained. ; To what extent the downward extension of the pelagic fauna is governed by conditions of temperature, or in how far this limitation is dependent principally upon the presence or absence of light as a determining factor in the evolution of plant life, still remains to be ascertained. Forel, in 1874, found that paper sensitised with chlo- ride of silver was still acted upon by the diffused light of the Lake of Geneva at a depth of about forty-five metres in summer and one ’ hundred metres in winter, while ordinary shining objects disap- peared from view at a depth of sixteen to seventeen metres. Asper, in August, 1881, obtained positive results through the use of plates sensitised with an emulsion of bromide of silver at a depth some- what exceeding ninety metres in the Lake of Zurich; and more re- cently (1884~’85) Fol, Sarasin, Pictet, and others, have been able to detect the penetration of light in Lake Geneva to a maximum depth (in winter) of two hundred metres. In summer the penetra- tion is considerably less. Fol] and Sarasin *! have also demonstrated that, in the Mediterranean, the solar rays penetrate to a depth nearly double that to which they were found to descend in the Swiss lakes, or to four hundred metres, and that at a depth of three hundred and eighty metres the intensity of light is as great as in Lake ‘ LAKE FAUNAS. 129 Geneva at one hundred and ninety-two metres. At this depth, however, the impression produced upon the sensitised plates was of no greater value than that which would have been produced, under ordinary conditions, on a clear night, without a moon, A remarkable feature of the lacustrine fauna is the very broad distribution of most of the species. Not only is there a general resemblance between the pelagic faunas of all the European lakes that have thus far been examined, from Scandinavia to Italy, and from Italy to Bohemia and the Caucasus, but a strict identity, at least as far as the species of Entomostraca are concerned. The species that occur in the one lake are also the species of the other lakes, although the respective littoral and deep faunas may be largely distinct. Further, it would appear that the same species are constituents of the pelagic faunas of American lakes as well, and not improbably make up the greater part of them. Professor 8. I. Smith, in his investigations of the fauna of Lake Superior, determined the presence, in the surface waters, of Daphnia galeata and Leptodora hyalina, common forms in the lakes of both Southern and Northern Europe, and of Daphnia pellucida, which was de- scribed by Miller as a pelagic inhabitant of some of the Danish waters. As to the origin of the pelagic fauna little positive is known. That it is not a direct derivative of the different littoral faunas is very nearly certain, for were this the case we should expect to meet with largely differing assemblages of pelagic forms in all lakes where the littoral or deep faunas likewise differ; but, as has been seen, this is not the case. Yet there can be little or no question that it really represents a modification of some primary shore-fauna, whose members, through force of circumstances, were compelled to adapt themselves to new conditions of existence. The supposed method of its differentiation and further distribution is thus indi- cated by Forel: ‘‘I believe we must find the cause of the differ- entiation of the pelagic fauna in the combination of two different phenomena — namely, the daily migrations of the Entomostraca, and the regular local winds of the great lakes. It is well known that on the borders of great masses of water two regular winds - prevail, one of which blows at night from the land towards the water, the other by day from the water to the land. The nocturnal animals of the shore-region, which swim at night at the surface, 10 130 GEOGRAPHICAL DISTRIBUTION. are at this time driven towards the middle of the lake by the sur- face-current of the land-winds, sink during the day, being driven away by the light, mto the deep water, and thus escape the surface- current of the lake-winds, which would otherwise have carried them again to the shore. Constantly driven farther every night, they remain confined to the pelagic region, as they are not carried back again during the day. Thus a differentiation takes place by natural selection, until at last, after a certain number of genera- tions, there remain only the wonderfully transparent and almost exclusively swimming animals which we know. When this differ- entiation has once taken place, the pelagic species is conveyed [in the condition of resting eggs] by the migratory water-birds from one country to another, and from one lake into another, where it reproduces its kind if the conditions of existence of the medium are favourable. In this way we may find the pelagic Entomostraca in lakes which are too small to possess the alternation of winds, the animals having been differentiated by the action of the winds in other larger lakes.” It might, however, be asked with Pavesi, if the general uni- formity of pelagic faunas has been brought about through a method of distribution such as is here indicated, how has it happened that some lakes should be so largely deficient in pelagic forms as com- pared with other, and nearly contiguous, lakes? The lakes of Northern Italy may be taken in illustration of a condition of this kind. Seeing that identical forms have been scattered to such widely separated quarters of a continent, as Italy, Scandinavia, and the Caucasus, it certainly appears a little surprising that immedi- ately adjoining districts should have been so irregularly stocked with the distributed material. It might, however, be conceived to be a matter of accident, and, indeed, at first sight the condition appears to be more in the nature of a support to the theory stated than as an argument against it. But if accidental conditions of this kind have happened, why has it not also accidentally happened that some of the lakes should have retained a fauna, formed through modification of their own particular littoral or deep fauna, distinct from that of any other lake? Still, the objection here raised is not an insuperable one, and offers much less difficulty in the way of the partial solution of the problem than does the circumstance of the oc- currence of identical forms in the lakes of Europe and North America. LAKE FAUNAS. 131 , Deep Faunas of Lakes.—The most systematic and thorough investigations that have been made into the nature of deep lacustrine faunas are those of Forel upon the fauna of Lake Geneva. As the result of the observations of this naturalist it would appear that the abundant fauna of the floor of this lake comprises representa- tives of nearly all the primary divisions of fresh-water—inhabiting Invertebrata, and that even a fair proportion of the secondary groups are also represented, although by a very limited number of species in nearly all cases. Included in the lowest forms are sev- eral ameebe, and Epistylis, Opercularia, and Acineta among infu- sorians. The hydroids are represented by the common brown hydra (Hydra rubra—to one hundred metres), and the rotifers by Flos- cularia. Three orders of worms are indicated—nematoids, cestoids, and turbellarians—and two of annelids proper, the hirudines and chetopods (Lombriculus, Tubifex, &c.}. The turbellarians (Pla- naria, Mesostomum, Dendroccelum) have no less than eleven species, one of which, Vortex Lemani, is found at all depths between fifteen and three hundred metres. A cestoid was dredged from a depth of two hundred and fifty-eight metres. The crustaceans are repre- sented by a limited number of species belonging to the amphipods (Gammarus cxcus), isopods (Asellus cecus), cladoceres (Lynceus), ostracods (Cypris, Candona), and copepods (Cyclops, Canthocamp- tus). Other articulates are four or five species, and as many genera, of arachnids (Arctiscus, Hydrachnella, &c.) and the larve of some tipuliform insects. The limited number of mollusks inhabiting the depth is not a little remarkable; of the lamellibranchs there is the single genus Pisidium, with about three species, and of the gastero- pods only the genera Limnea and Valvata. Although the Unioni- de (Anodon) are very abundant in the littoral fauna, they are com- pletely absent below. One species of Limnea (L. abyssicola) was found to be sufficiently abundant at a depth of two hundred and fifty metres, a circumstance to which Forel calls attention as indi- cating the readiness with which an air-breathing mollusk can ac- commodate itself to conditions largely at variance with those which are considered necessary to conform to certain structural peculiari- ties.* * When brought to what might be considered its proper position, the sur- face of the water, the mollusk almost immediately adapted itself to the new conditions of existence, apparently without undergoing any inconvenience. 132 GEOGRAPHICAL DISTRIBUTION. Although the fauna, taken as a whole, may be said to possess certain special characters, yet, broadly considered, it is only the representative, by slight modification, of the fauna of the littoral zone. It possesses no really well-defined or abnormal features of its own. Most of the forms are of small size, and a number of them, whose surface representatives are active and good swimmers, appear to have taken to sluggish habits; neither Cyclops nor Lynceus would rise when placed in an aquarium. Blindness is exceptional, and it is a surprising fact that the animals suffering from this defect (Gammarus cecus, Asellus ceecus) are comparatively shallow-water forms (thirty metres), whereas those living at the greater depths, down to three hundred fathoms, are well provided with visual organs. The faunas of different zones of depth do not appear to differ sensibly from one another, except in the elimination or excess of a number of species. The greater number of these would seem to be distinct from their analogues of the littoral zone.* Many of the species found in Lake Geneva are identical with forms found in the other Swiss lakes, and in the lakes of Savoy, as identified by Imhof, and there is good reason for supposing that a general analogy, if not absolute identity, unites the different deep lacustrine faunas of the same region. Professor Smith obtained from deep water (exceeding fifteen fathoms) in Lake Superior ™ Hydra carnea (from eight to one hundred and forty-eight fathoms), a Pisidium (from four to one hundred and fifty-nine fathoms), several species of worms (Senuris, Nephelis, Tubifex, &c.), the larve of various tipulids and ephemerids, and among crustaceans Mysis relicta and Pantoporeia affinis (from shallow water to one hundred and fifty-nine fathoms). The last two, which were also found by Stimpson in Lake Michigan, are forms belonging to Lake Wetter in Sweden, supposed by Lovén to have been derived by modifica- tion from marine species. * So stated by Forel in his report of 1876, although in 1874 he and Plessis appear to have maintained the opposite view. PART II. GEOLOGICAL DISTRIBUTION. 1. The succession of life.—Faunas of the different geological periods. THERE is no fact more patent in the history of the organic world than that there has been from first to last a progressive evo- lution from lower to higher forms in the chain of beings that suc- cessively peopled the earth’s surface. Casting our eye back over the vast series of rock deposits which together constitute the fossili- ferous scale of geologists, from the Cambrian to the Post-Pliocene, and which together have a maximum development of probably not less than two hundred thousand feet (or forty miles), we re- mark along the most ancient horizon the traces of animals which bespeak the organisation of some of the lowest forms of life with which we are at present acquainted; in the middle distance we note the appearance of forms whose organisation marks a decided advance upon that of their predecessors; and, finally, in the fore- ground, we are brought upon the threshold of those highly com- plicated forms which to-day people the surface of the earth. The simpler forms of life came into existence first; the most complex last. It must not be implied, however, that with the progressive and steady evolution of higher forms there has been an equally progressive destruction or elimination of the forms of lower or- ganisation; both have kept pace with each other, so that, at the present day, although innumerable groups have completely disap- peared, the lowest is found flourishing side by side with the highest. This inter-association of lower and higher forms has manifested it- 134 GEOLOGICAL DISTRIBUTION. self in all the geological formations that are known to us, from the Cambrian period to the present day, and there can be no doubt that, were a fossiliferous formation discovered of older date than the Cambrian, or immediately underlying it, we should find pre- cisely the same juxtaposition, although to a more limited extent, of organisms of higher and lower development. Only then when we could fathom the first-born deposit, or trench upon the period when life first came into existence, would we, in all probability, be circumscribed in our survey to animals exhibiting a nearly uniform low grade of organisation. Such a point has probably not yet been reached, or, if reached, its existence can only be indicated with doubt, since the oldest rock deposits (the Laurentian) into whose composition an organic element unquestionably largely en- tered have lost all or nearly all traces of their primary fossiliferous character. With this wholesale obliteration have, consequently, disappeared the traces of the earliest and most primitive types of life-forms. If Eozoon and Archeospherina, from the Laurentian limestones, be considered actually to represent organic forms, as is maintained by many prominent geologists and naturalists, then, indeed, are we presented with a large series of deposits in which apparently all the organic elements belong ‘to one uniformly low type—the type of the Foraminifera—not yet the lowest, but very nearly it. But even granting the animal nature of the two structures here indi- cated, it would yet be very unsafe to affirm that they represent the only forms of life that tenanted the earliest seas; multitudes of other forms may have flourished and perished, and left no traces behind them, or had their traces completely obliterated at some remote subsequent period. We should then be no wiser for their existence. The succeeding Cambrian period ushers in with it such a host of multiform beings—beings of comparatively high organisation—that it becomes almost impossible to conceive that their ancestry should date back only to a period so little removed from the Cambrian as the Laurentian, unless, indeed, the hiatus separating the Laurentian from the Cambrian is very much greater than is indicated by its stratigraphical position. But if the an- cestral forms of the Cambrian stock already existed in the Laurentian seas, what has become of their remains? Why is it that in these oldest so-called fossiliferous rocks we meet with only Eozoon and CAMBRIAN FAUNA. 135 Archexosphetrina? Surely it could not have been that there was such a disposition of the remains as to leave nothing but these two forms belonging to the lowest type. It appears far more plausible to assume with those who uphold the mineral nature of Eozoon and Archeospherina that we have no traces of this ancient pre- Cambrian fauna remaining, and that, consequently, the destruction was complete. How far back beyond the Laurentian the root of the present existing chain of organisms may have extended it is impossible even to conjecture. Cambrian Fauna,—It is certainly a surprising fact, whichever way it be considered, that, with the formation bringing the first unequivocal evidences of organic life, we should meet with that multiplicity and variety which characterise the faunal assemblage of the Cambrian period. Most of the greater divisions of the ani- mal kingdom, possibly not even excepting the vertebrates, were there represented, and most of these already in the lowest or oldest deposit —protozoans, ccelenterates, echinoderms, worms, articulates, and mollusks. And more than this, some of these groups were already represented by a full, or nearly full, com- plement of the orders that have been assigned to them by natu- ralists, and which include all the various forms that have thus far been discovered as belonging to the groups. Thus the Cam- brian echinoderms are represented by forms belonging to three out of the six usually recognised orders—the Cystidea, Crinoidea (ocean-lilies), and Asteroidea (star-fishes). The last two have repre- sentatives living at the present day, whcreas the former is entirely extinct. We have here, then, the most ancient ocean-lily and star- fish (Palasterina), and it is interesting to note what distinct rela- tions these two forms hold to their modern representatives. While the Crinoidea attained their maximum development in the seas of the Paleozoic period—Silurian, Devonian, and Carboniferous—since which time they have been pretty steadily declining, until at the present moment they are represented by scarcely more ‘than a half- dozen distinct generic types, the Asteroidea have teen just as stead- ily increasing, and, indeed, attain their maximum development in the modern seas. It may appear at first sight anomalous how two groups, so widely dissimilar from each other, and having such varying developments, should have appeared simultaneously in the same period of the 136 GEOLOGICAL DISTRIBUTION. earth’s geological history, the Cambrian. But it must be borne in mind that in the Cambrian formation we have only what is seem- ’ ingly the oldest fossiliferous formation, and that the ancestral forms of both ocean-lilies and star-fishes lie buried in rock deposits of undeterminably older age. If, on the hypothesis of evolution, we uphold the inter-derivation, or derivation from one another, of these two forms, then it is but fair to assume that the crinoid, which is structurally the lowest, appeared at a period considerably anterior to the star-fish, which must have required for its specialisation a no inconsiderable lapse of time. And it is a singular fact, and one strikingly confirmatory of this view of relationship, that we have in both these forms certain peculiarities of structure which effect a sort of transition from the one to the other. Thus, in some of the fixed crinoids the plume or tuft separates from the column after a certain period of existence, and then leads an independent exist- ence, to all appearance a stellarid (the Comatula). Conversely, the officers of the late ‘‘Travailleur” deep-sea dredging expedition obtained off the coast of Spain, and from depths respectively of nineteen hundred and sixty and twenty-six hundred and fifty metres, two individuals of a new genus of star-fish (since named by Perrier Caulaster peduncularis), which exhibited on the dorsal surface a true peduncle, demonstrated to be absolutely homologous with the stalk of the crinoid. Yet, despite this obvious relation- ship, it is not a little surprising that no pedunculated star-fish has thus far been found fossil, nor any comatulid crinoid to antedate the Jurassic period (Antedon). The Cambrian Mollusca comprise representatives of five of the six classes that now inhabit the seas, namely, the Brachiopoda, Acephala, Pteropoda, Gasteropoda, and Cephalopoda. Here again, therefore, we have an apparent simultaneous appearance of lower and higher forms; but, as before, we must look to a much earlier period for the ancestral traces, if any have been preserved, of the first or most primitive type. The genetic relationships of these various molluscan groups cannot, in the present state of the science, be determined with any degree of certainty; but, if a low degree of organisation indicates antiquity, which certainly appears to be the case with many groups of animals, then it may be fairly assumed that the Brachiopoda were the first to appear. It is a surprising fact in the history of these animals, and one which is, perhaps, not CAMBRIAN FAUNA. 137 repeated to the same extent in any other group, that while hosts of genera, and even complete families of this order, which flourished in the seas intermediate in time between the Cambrian period and our own day, should have successively disappeared, a few individual types seem to have survived from first to last, without having un- dergone any essential modification of structure. Thus, the Lingula, or Lingulella, of the Cambrian rocks is but very little, if at all, dif- ferent from the existing Lingula, and it has indeed been considered doubtful by some authors whether even specific characters could be assigned to distinguish some of the earlier from the later forms, separated by an interval of millions of years. The same persistence of type is represented in the genus Discina. Side by side with these lower molluscan types, but appearing at a somewhat later period, the Upper Cambrian, we find, as has al- ready been stated, forms belonging to the highest order, the Cepha- lopoda (Orthoceras, Cyrtoceras), another apparent contradiction to the doctrine of progressive higher development. Considering the group of the cephalopods by itself, however, we observe that its earliest types belonged to the lower of the two divisions into which the cuttle-fishes have been divided—the tetrabranchiate, or four- gilled order—a division to which the somewhat later appearing, and now probably disappearing, Nautilus also belongs. These primitive cephalopods were succeeded in time by other members of the same order—Gyroceras, Nautilus, Goniatites—until the Tri- “assic period was reached, when the first dibranchiate form, Belem- nites, appears. From this period down to the close of the Meso- zoic era both the two-gilled and the four-gilled forms occur in such abundance that it would be almost impossible to state to which group belonged the preeminence. But in the meanwhile a general alteration and succession in the representative cephalopod type had been taking place. The early forms already mentioned, Orthoceras, Gyroceras, Cyrtoceras, and their allies, belonging to the family of the Nautilide, are succeeded in the Triassic period, where their last traces (excepting Nautilus) are to be met with, by the members of the more complicated group of the Ammonitide, whose earliest precursors (three or more species from the Carboniferous formations of India, and a solitary species from the Carboniferous of Texas) would seem to have been foreshadowed by Goniatites, a type struc- turally intermediate between the Nautilide and the Ammonitide. 138 GEOLOGICAL DISTRIBUTION. Similarly, in the case of the Cephalopoda dibranchiata, the Belem. nitide are succeeded by forms more nearly resembling the cala- maries, or cuttle-fishes (Teuthide), of to-day, whose remains are found already in the Jurassic deposits (Onychoteuthis, Teuthop- sis, Belemnosepia). With the beginning of the Tertiary period * we note the final disappearance of the varied group of the Ammoni- tide, and with them the last traces of all but one of the lower or four-gilled order of cephalopods. The single exception is the Nautilus, which, as a persistent type, almost unaltered from the Silurian to the present period, alone survives to contest the seas with the members of the higher or dibranchiate order. The predominant Mollusca of our modern seas, the Gasteropoda and the Acephala, were but feebly represented in the seas of the Cambrian period; but it seems not improbable that some of the earliest forms—e.g., Capulus, Pleurotomaria, among the snails— belonged to types absolutely identical with those living at the present time. It is not until we have completely passed over the Paleozoic era, which, so far as the Mollusca are concerned, may be said to constitute the age of the Brachiopoda, that these two orders of shell-fish attain any special significance. From the beginning of ‘the Mesozoic era onward they steadily crowd the deposits with their remains, until, finally, with the Tertiary formations, and the forma- tions succecding these, they constitute the most characteristic and most important invertebrate landmarks to the geologist and paleon- tologist. It has been contended, and with apparent force, that the irregu- lar appearance in time of the Mollusca—i. ¢., the almost simultane- ous introduction of forms belonging to both the lowest and the highest orders, and the final supremacy in the existing seas of the type of the Acephala, a group of mollusks inferior in organisation to the Cephalopoda, the Gasteropoda, and the Pteropoda—is in- compatible with the doctrine of evolution, which, as argued, re- quires for its confirmation the introduction first of the lower forms, the development from these of the more advanced, and, ultimate- ly, the appearance of those that are most perfect or specialised in structure. It must be recollected, however, that, as far as the al- most simultaneous introduction of lower and higher forms is con- * A species from the Lower Tertiary of California. CAMBRIAN FAUNA. 139 cerned, the obstacle is more apparent than real, for, as has already been insisted upon, it is impossible to determine how far back be- yond the Cambrian, or first unequivocally fossiliferous formation, life may have already existed, and, consequently, to what very ancient period the ancestry of the molluscan type may extend. As a matter of fact, the most ancient mollusk, the Lingula, or Lingu- lella, is almost the lowest in structure of any with which we are acquainted, and if in the rock deposits we meet with its remains but barely antedating those of the very much more highly organ- ised Orthoceras, we have yet strong grounds for concluding that its first appearance was very much earlier, only that, through the gen- eral obliteration of all remains in the preceding geological period, direct evidence to that effect has been lost. As to the other objec- tion, that the predominant forms persisting at any given epoch should be those whose structure manifests the highest development, it may be remarked that the evolutionary force requires no such result as the outcome of its operative action. It is among such forms as, in their mutual relations to their surroundings, whatever these may be, are best adapted or fitted for combatting the nu- merous elements that constantly interpose themselves in the path of existence, that we must look for examples of greatest persistence and development—for the survivors in the struggle for existence. Hence, while the highest developed forms in any given series of animals will present themselves in or about the period most re- moved from the birth of that series, yet it need not follow that the higher series will ultimately outlive, or even predominate over, the representatives of a lower parallel series of the same class of animals, whose fitness for struggling in the battle for existence is not infrequently vastly superior to that of the higher class. We need not be, therefore, surprised at finding, in a given class of ani- mals, some of the more perfect forms disappearing from the world’s horizon before the less perfect, and these last, consequently, the survivors in the general battle for life. But, while no general law can be formulated regarding the disappearance, as conditioned by the degree of perfection, of the various series of a given class of animals, or, regarding their relative development in any one period of the earth’s history, the law of appearance or succession already stated—i. e., the introduction of lower forms before those of a higher order—can very generally be maintained. 140 GEOLOGICAL DISTRIBUTION. An objection to the evolutionary doctrine, similar to that which has been drawn from the distribution of the Mollusca, is also fur- nished by the articulated animals, or, more particularly, by the class of the Crustacea. The members of this class boast of a lineage, as far as has yet been determined, very nearly, if not fully, as ancient as that of the Mollusca, one extending back to the earliest Cambrian period. But, while the most ancient mollusks with which we are acquainted belong in great part to orders, families, and even genera, whose representatives still flourish in the existing seas, the most ancient crustaceans, or at least the majority of them, the Trilobita, have long since become totally extinct; hence the impossibility of determining their true relationships. However uncertain or obscure this relationship may be, whether it is with the Phyllopods, as claimed by some, or, what is much more likely, with the Xiphosura (king-crabs) and arachnids, as argued by others, there can be no doubt, if homologies of structure can be relied upon, that the mem- bers of this group of animals represent a high grade of structural organisation, and especially if the period of their appearance is taken into consideration. But here, just as in the case of the Mollusca, we have the strongest evidence for concluding that their earliest appearance dates far beyond the Cambrian period, as is proved almost conclusively by the simultaneous appearance in the oldest Cambrian strata of some of the simplest and most compli- cated trilobitic forms, Agnostus and Paradoxides, which are at the same time also among the smallest and the largest forms of the entire order. A further evidence of the pre-Cambrian antiquity of this group is furnished by the circumstance of the abundance in which the earliest remains are found, an abundance which, though perhaps not equal to that characteristic of the succeeding Silurian and Devonian trilobitic faunas, is yet sufficient to impress a dis- tinct individuality upon the fauna of the period. While with the Cambrian trilobites we find associated other forms of crusta- cean animals, such as the phyllopods (Hymenocaris) and ostracods (Primitia, Leperditia), the highest members of the class, the Deca- poda (crabs and lobsters), appear not to have been as yet evolved. Indeed, it is not until the entire Silurian period and a considerable portion of the Devonian are passed that we mect with an example of the ten-legged order of crustaceans. Barely had these higher forms asserted themselves on the field of life ere a decline in the CAMBRIAN FAUNA. 141 supremacy of their predecessors is made manifest. With the mid- dle of the Devonian period the beginning of the trilobitic decay becomes apparent, and, after the close of that period, 7. ¢., in the Carboniferous, less than a half-dozen types remain, and even these are of comparatively rare occurrence. At the close of this last- named period the trilobites disappear totally and forever from the scene. * Broadly looking over the Cambrian fauna, we find it to be dis- tinguished by two important features. One of these is the fact that it is entirely destitute of both land and fresh-water forms, or such as are strictly adapted to breathing directly the oxygen of the atmosphere or that of fresh water. All the forms thus far encoun- tered are, as far as we know, of a strictly marine nature. The ab- sence of land animals will scarcely appear surprising in view of the complete, or nearly complete, absence of a land vegetation, and the correlative want of the nourishing material requisite for that charac- ter of organisms. The absence of fresh-water forms is not so readily accounted for, unless it be that there were formed at that time no fiuviatile or lacustrine accumulations of sufficient magnitude to have left their traces behind them. It is not impossible, however, that some, or even many, of the recognised marine fossils, or such as have a marine habit, of the Cambrian formation, are in reality estuarine or brackish forms, as it can scarcely be conceived that all the deposits that were formed at the mouths of the ancient rivers should have been so totally destroyed or covered over as to have left absolutely no vestiges of their former existence. Doubtless, some of these have been preserved, along with their contained fos- sils, although the exact nature of such deposits may be disguised from us by reason of our imperfect knowledge concerning the true habits of their representative organisms. Nor would it be abso- lutely safe to affirm that some of these organisms, undistinguishable from what at the present day are indisputably marine types, may not in reality have been of a purely fresh-water habit in those early days. The other distinguishing feature of the Cambrian fauna is the *Shumard has described representatives of the genera Phillipsia and Proetus in deposits of the Sierra Madre, of the Southern United States, claimed to belong to the Permian period; the determination of age may be considered to be very doubtful, however. 142 GEOLOGICAL DISTRIBUTION. absence of positive indications of the existence of vertebrated ani- mals. The only objects that have thus far been described as per- taining, with any show of probability, to the members of this highest division of the animal kingdom, are the singular bodies known as conodonts, which, in the opinion of their discoverer, Pander, and of some other naturalists, represent the teeth of fishes belonging to the order of the myxinoids (hags and lampreys), with the exception of the lancelet (Amphioxus) the lowest of the entire class of Pisces. The weight of opinion, however, seems to relegate these problem- atical bodies to the Invertebrata, and not improbably, as has been urged for some of these forms, they represent the jaw-teeth of cer- tain annelids. Silurian Fauna.—The fauna of the Silurian period marks a decided advance upon its predecessor. The chain of organisms which, with the exception of the somewhat doubtful conodonts, was hitherto constituted exclusively by the members of the inver- tebrate series—sponges, echinoderms, mollusks, articulates—exhib- its here for the first time indisputable representatives of the more highly organised group of the vertebrates; but not until the Upper Silurian deposits are reached. We here meet with the remains of two distinct orders of fishes, the sharks or dog-fishes (Elasmo- branchii), as represented by Onchus and Thelodus, and the bucklered Ganoidei—Pteraspis—the former still very abundant in the modern seas; the latter, which include, among other forms, the sturgeon and alligator-gar, probably nearly verging on extinction.* In both these orders the osseous framework or skeleton is frequently in a more or less imperfect condition—complete ossification being the exception rather than the rule—and hence, in so far, these primi- tive vertebrates exemplify a low grade of organisation compared with those—like the bony fishes, and most of the animals above them—in which the vertebral column is completely ossified, or reaches its furthest development. Nor are other characters want- ing proving ‘inferiority of organisation. We have here, therefore, another illustration of the very important fact—a fact sustaining the inference of the progressive evolution of higher from lower * The oldest fishes were, until recently, supposed to belong to the British Ludlow beds; but the discovery, by Professor Clay pole, of ichthyic fragments in deposits below the ‘* Water-Lime”’ of Pennsylvania would seem to remove them stil! farther back in the geological scale. SILURIAN FAUNA. 143 forms of life—that the representatives of each class of animals were first ushered in in their simplest or most embryonic forms, and that not until these had attained a considerable development was there a noticeable appearance of the more highly constituted forms. It is a significant (even if not a very remarkable) fact that, prior to the first introduction of this lowest class of the Vertebrata, all the larger divisions of the Invertebrata, as now recognised by natu- ralists, had already come into existence. Of these, the diversity of form in the Silurian deposits, no less than the numerical de- velopment, is very great, and equally so in almost all the classes represented. The most marked feature of the Silurian invertebrate fauna, as contrasted with the Cambrian, is furnished by the corals, which, barring a few forms doubtfully belonging to the Cambrian of Sweden, have here their earliest representatives. These primitive types of the Actinozoa, as well as nearly all others of the Paleozoic series of deposits, have generally been recognised by naturalists to constitute two well-defined groups, the Tabulata (Favosites, Haly- sites, Heliolites, Alveolites, &c.) and the Rugosa, or cup-corals (Cy- athophyllum, Streptelasma, Omphyma, Zaphrentis, &c.), in both of which the calyces are divided up into superimposed chambers by transverse plates or tabula—the former with very rudimentary septa, the latter with the septa well developed, and the outer calicular wall greatly thickened. In the majority of these cup-corals the septa are disposed in multiples of four (Tetracoralla), whereas in nearly all recent Madreporaria this disposition is effected in multi- ples of six (Hexacoralla). Our recently acquired knowledge of the deep-sea fauna, and a more intimate acquaintance with the anatomy of some of the more aberrant species of coral, tend to show that the supposed sharp delimitation of the Paleozoic actinozoan fauna does not in reality exist. The tabulate corals, for example, whose final extinction with the Paleozoic era has generally been insisted upon as one of the most decisive of geological landmarks, would seem to hold a number of forms more or less closely related to types living in the modern seas, which in themselves combine most diverse features in their organisation. The genera Halysites and Syringopora appear to be not distantly removed from the recent organ-pipe (Tubipora); Favosites is placed among the -Poritide; and Heliolites not impossibly represents an ancestral form of the 144 GEOLOGICAL DISTRIBUTION. group to which the modern Heliopora, recently claimed to be an alcyonarian, also belongs.* The rugose-corals, apart from the very limited number of forms which occur fossil in deposits newer than the Paleozoic—? Holocystis (Cretaceous), Conosonilia (Tertiary)— have apparently two living representative types in Guynia and Hap- lophyllia. On the other hand, the modern star-corals, if we exclude from this group the Favositide, have but a feeble development in the earlier deposits, although several recent families are represented (Poritide, Eupsammide, Astreide). Of the genera belonging to this group, Protarea, Stylarsea, Prisciturben, and Calostylis date back to the Silurian period. The remarkable development of corals in the Silurian seas makes it not a little difficult to account for the total, or almost total, ab- sence of their remains in deposits of the preceding Cambrian age. It is scarcely credible that the animals of this class should not have already then existed; but if so, what has become of them? In ex- planation of this anomaly some geologists have urged that the strata of Cambrian age which contain recognisable fossils are all of a deep-sea origin, and that in the shallow and littoral deposits, where we might be expected to look for the traces of the organisms in question, organic remains have been completely obliterated through rock-metamorphism of one kind or another. The evi- dence supporting this hypothesis is, however, far from satisfac- tory, and the problem must be considered as one still awaiting solution. The graptolites, a group of organisms whose earliest remains are found in the transition rocks which unite the Cambrian and Silurian formations, and whose organisation appears to be most nearly reflected in that of the recent sertularians or sea-firs of the class Hydrozoa, constitute an important element in the Silurian * The reference of Favosites to the Poritide, it must be confessed, is based upon rather slender evidence, and perhaps scarcely less so the placing of Heliolites among the Alcyonaria. Hérnes (‘‘ Elemente der Paleontologie,” 1884) justly emphasises the artificiality of a classification in which the number and disposition of the septa and tentacles are made the basis for a division into primary groups, and in which other equally important characters are com- pletely lost sight of. The relationship existing between past and recent forms, taken in conjunction with the general homogeneousness of character exhibited by the Tabulata, would seem to imply that the classification of the recent Actinozoa requires serious emendation. SILURIAN FAUNA. 145 fauna, becoming practically extinct with the close of that period.* It is a noteworthy circumstance in connection with the history of this family that the more complicated or double-stemmed forms, such as Diplograptus, Didymograptus, Phyllograptus, and Dichograptus, preceded, in the order of appearance, the simple-stemmed forms, like Monograptus and Rastrites, proving, contrary to what might have been naturally supposed, that the latter were not the ancestral types of the family. On any evolutionary hypothesis the simpler forms appear to have been brought about as the result of degeneration. In modern type hydrozoans the Silurian, as all other Paleozoic, de- posits are very deficient, a circumstance, doubtless, due in con- siderable part to the perishable nature of the organisms belonging to this class. The impressions of jelly-fishes have, however, been indicated in both the Cambrian and Silurian rocks of Sweden. Stromatopora, a very broadly distributed genus, whose affinities are now generally conceded to be with the Milleporida, passes into the Devonian formation. Of other Invertebrata, such as the echinoderms, mollusks, and articulates, there is a vast profusion of forms, which, apart from the mere matter of numbers, are in many respects sharply contrasted with their predecessors of the Cambrian period. The brachiopod mollusks, the predominant forms of which, as Spirifer, Atrypa, Athyris, Strophomena, Rhynchonella, and Pentamerus, belong to the group of the Brachiopoda articulata, are structurally consider- ably in advance of the inarticulate genera Lingula, Lingulella, Discina, and Obolus, which make up almost the whole of the corresponding Cambrian fauna; the latter, as far as is known, con- tains but a single precursor of the articulate division, Orthis. The prodigious development of the Silurian Cephalopoda would of itself be sufficient to distinguish the period from the period preceding. While up to the present time only two species of this class, an Orthoceras and a Cyrtoceras, are positively known from Cambrian deposits, no less than eleven hundred species, referable to a very considerable number of genera of Nautilidee—Orthoceras, Cyrto- ceras, Gyroceras, Endoceras, Gomphoceras, Phragmoceras, Lituites, Nautilus, &c.—have been described from the Silurian basin of Bohe- mia alone. The total number of species of this period may be * The somewhat problematical Dictyonema passes into the Devonian: Triplograptus, if a true graptolite, is Devonian. 146 GEOLOGICAL DISTRIBUTION. estimated at between two and three thousand. The genus Gonia- tites, which effects a partial transition between the Nautilide and the Mesozoic ammonites, appears for the first time in the later Silurian deposits. It is a surprising fact, considering the remarkable development of the Cambrian trilobitic fauna, that not only are none of the earlier species represented in the Silurian deposits, but that by far the greater number of generic types, and more particularly those which by a special individual or specific development are rendered most important, as Paradoxides, Dikelocephalus, Olenus, Sao, and Conocephalus, should be also wanting. Only seven out of some twenty-seven genera of the primordial zone connect the formations of the two periods. The Silurian Trilobita comprise probably in the neighbourhood of fifteen hundred species, referable to some fifty or more genera; yet of this vast number there are barely a half-dozen species which transgress the boundaries of the formation, passing into the Devonian. Among the more abundantly represented gen- era are Phacops, Dalmania, Calymene, Asaphus, Trinucleus, Aci- daspis, and Cheirurus. Viewed irrespective of numerical development, the most signi- ficant feature connected with the Silurian invertebrate fauna is the introduction of the earliest ‘‘air-breathers.” Until recently these were supposed to belong to the period following, the Devonian, but the discovery of a true scorpioid (Paleeophoneus) in the Upper Silu- rian deposits of both Sweden and Scotland, and of an apparent orthopteroid (Paleoblattina) in the nearly equivalent deposits of Calvados, France, proves conclusively that a very considerable differentiation among the air-breathing arthropods had already taken place, and points to a period very much more ancient for the first origination of the group.* Devonian Faun2,—The primitive air-breathing arthropod fauna just referred to finds a somewhat larger extension in the rocks of Devonian age, where fragments belonging to some five or six spe- cies of insect, possibly representing as many genera—Platephemera, Gerephemera, Lithentomum, Homothetis, Xenoneura, Discrytus— have been discovered. These appear to belong to the modern * The seorpion described by Professor Whitfield (‘‘ Science,’ July 31, 1885) from the Upper Silurian rocks of New York may, as suggested by Mr. Pohlman (‘* Science,’? September 4, 1885), prove to be a young eurypteroid. DEVONIAN FAUNA. 14? group of the netted-veins (Pseudoneuroptera and Neuroptera), although by some authors they, as well as all other Paleozoic insects, are considered to represent a distinct, and now wholly extinct, type of Insecta, the Paleodictyoptera. In whichever way their relationship be viewed, there can be little doubt that they represent very nearly the lowest structural type of their class. It is a very remarkable fact that the wing venation of these primi- tive insect forms is practically identical with that which charac- terises the modern insects belonging to the same group or order; the vast lapse of ages between the Devonian period and our own day appears to have effected no essential modification of structure in this particular direction. Besides these neuropterous forms, certain wing fragments have been referred to the members of the higher order Orthoptera, to which the modern grasshopper and cockroach belong. But there seems to be considerable doubt as to the claims of the so-called Devonian cockroach,* and it would, perhaps, be as well to consider its position as still a matter of un- certainty. The marked differentiation exhibited by the Devonian insects indicates that they were far more numerous than would appear from the paucity of their remains, and the inference drawn as to their great antiquity has been confirmed by the discovery of the Upper Silurian -form already referred to. Coincidently with the appearance of these early inhabitants of the land surface, we remark the first considerable development of a land vegetation, whose earliest traces are to be met with in the Silurian period. With but very few exceptions (certain forms, as Prototaxites, Ormoxylon and Dadoxylon, considered by some authorities to represent true conifers, the first of their kind) all the Devonian plants belong to the lower or non-flowering division, the Crypto- gamia, comprising a multitude of ferns, tree-ferns, giant representa- tives, like Sigillaria and Lepidodendron, of the modern club-mosses (Lycopodiaceze), and scarcely less gigantic forms (Calamites, Cal- amodendron, with Annularia, Asterophyllites, Sphenophyllum) be- longing to the group of the horse-tails (Equisetacee). Of Invertebrata other than insects the Devonian fauna is very rich in forms; but these show a marked similarity to those of the * Referred by Hagen to the Neuroptera. The same authority considers the age of the rock formation in which the other insect remains have been found as more likely Carbonitcrous than Devonian. 148 GEOLOGICAL DISTRIBUTION. preceding period. Approximately the same types are represented, and while in the case of certain families a diminution in the number and variety of their representatives is noticeable, in others there is a corresponding increase. The corals, echinoderms, cephalopods, and brachiopods have approximately the same value as in the Silu- rian period, and, indeed, several of the specific forms that are to be met with in the one formation are also seen in the other. Among the Devonian brachiopods we have the first appearance of the genus Terebratula, a form which has continued to flourish, although in constantly diminishing numbers, from that period down to the present time. With it are associated a number of other genera— Strophalosia, Productus, Uncites—which likewise appear here for the first time. The gasteropods are all of the holostomatous or round- mouthed type— Pleurotomaria, Murchisonia, Euomphalus, Loxo- nema, Holopea, Platyceras, &c.—while the lamellibranchs, which show a marked increase, both in numbers and variety of form, over their Silurian predecessors, belong, as far as it has been possible to ascertain, exclusively to the Integropalliata, or such as are devoid of a sinual inflection to the pallial line. The families represented are either Heteromyaria (Aviculide, Mytilide) or Dimyaria (Nucu- lide, Arcade, Astartide, Cardiide), no true Monomyarian being as yet known. We meet here with the first pulmonate, Strophites, a member of the modern family of snails (Helicide), and likewise with what appears to be the earliest unequivocal fresh-water inver- tebrate, a mussel of the genus Anodonta, or one very closely allied to it. It is here, therefore, that we have the earliest undoubted traces of a fresh-water formation. The trilobites among Crustacea manifest a very rapid decline, and, indeed, in some regions they appear to have completely died out with the close of this period. The giant eurypterids—Euryp- terus, Pterygotus, Slimonia—the most formidable of all known living and extinct crustaceans—which first appeared in the Upper Silurian formation, linger on into the succeeding Carboniferous period, when they forever disappear. The Devonian deposits, as has already been stated, contain the earliest remains of the highest order of crustaceans, the Decapoda, or ten-footers, which comprise the modern lobster and crab; the form in question (Paleopalemon) belongs to the macrurous, or long-tailed division, and is allied to the shrimps. DEVONIAN FAUNA. 149 The vertebrate life of this period exhibits a remarkable develop- ment as compared with that of the period preceding. But, as in the latter, all the remains belong to the class of fishes, and indeed principally, or one might say almost exclusively, to the same two orders, the elasmobranchs and ganoids. No animal of a grade higher than fishes had as yet appeared upon the scene, or, if possi- bly it had, no traces of it have thus far been discovered to indicate its existence there. To such an extent was the fish-fauna developed that the term ‘age of fishes” has not inappropriately been applied by paleontologists to designate this epoch of geological time. The preponderating types are the ganoids, which appear not only in forms that may be considered move or less remotely related to the type of the modern sturgeon (Macropetalichthys), or to the fringe- finned Polypteri of Africa (Holoptychius, Glyptolepis, Dipterus, Osteolepis), and the American alligator-gars (Chirolepis), but in such as have no representatives in any of the succeeding formations. These are the so-called ‘‘ bucklered ganoids,” which, in addition to the enamelled plates characteristic of this group of fishes, had the head and the anterior portion of the body encased in bony plates, more or less firmly united to each other, and serving as a protective armour. To this group, among others, belong Pteraspis, Cepha- laspis, Pterichthys, and Coccosteus, forms which had their forerun- ners already in the Upper Silurian deposits. Generally placed among the ganoids, and closely related to Coccosteus, are the giant Dinich- thys and Titanichthys, which appear to have attained a length of from twenty to thirty feet, and whose dental apparatus closely approximates that of the modern Lepidosiren, one of the lung-fishes (Dipnoi), a group of animals which effect a transition between the true fishes and the amphibians. If this relationship with Lepido- siren be absolutely established, as is claimed to be the case by many of the more prominent anatomists, then it is certainly significant that the advent of the Amphibia (the class of animals immediately above the fishes), in the succeeding Carboniferous period, is preceded by just that group which, in accordance with the principles and work- ings of evolution, we should expect to find interposed—the group which, on the one hand, combines some of the characters of the Amphibia, and, on the other, those of the ichthyic fishes. But, whatever the exact relationship of Dinichthys may be, there can be little question as to its representing a dipnoan type, or at least a 150 GEOLOGICAL DISTRIBUTION. transition form between the true ganoids and the lung-fishes. A similar position is occupied by some of the other crossopterygian fishes of the period, as Dipterus. Carboniferous Fauna.—The life of the Carboniferous period is marked by two important features: 1. The introduction for the first time of vertebrate animal forms higher in the scale of organisation than the fishes, 7. e., the amphibians; and 2. The great develop- ment of strictly air-breathing or terrestrial animals. Of these last we have at least four distinct types indicated—the Gasteropoda, Insecta, Arachnida, and Myriapoda. Of the first, which have a solitary forerunner in the Devonian formation, we are acquainted with a comparatively limited number of forms (Pupa, Anthraco- pupa, Dawsonella, Zonites), all of them more or less closely related to forms still living at the present day. The insects comprise not only members of the low order of netted-veins, which are the only forms known to be represented in the Devonian deposits, but those of the more highly organised Orthoptera, and not improbably also Coleoptera (beetles), although most of the remains referred to the latter order are now positively known not to belong there. The Orthoptera comprise, among other forms, some sixty or more spe- cies of primitive cockroach, the Paleoblattarie, which may be con- sidered to represent the ancestral type of the modern social pest (Blatta), whose earliest appearance dates from the Triassic period. To the same order belong the giant walking-sticks recently brought to light from the coal-measures of France, the Titanophasma Fayol- lei, which measure in length (in one specimen) upwards of twelve inches, and are, therefore, by linear measure, very nearly the largest of recent as well as fossil insects. This extraordinary development of a form, which may be taken to represent the extreme term of specialisation in an insect, in a period so early as the Carboniferous, is certainly not a little re- markable, and argues very strongly for the great antiquity beyond its own period of the origin of this class of animals. It is also not a little surprising that no representatives of the family of walking- sticks (Phasmida), other than those found in the Carboniferous deposits of France—Titanophasma and Protophasma—have as yet been found in a fossil condition, except such as may have been preserved in amber. Of the Neuroptera, the Haplophlebium Bar- nesii, from Nova Scotia, attained an expanse of wing of seven CARBONIFEROUS FAUNA. 151 inches, nearly equal to the expanse of the largest of the living dragov-flies, to which it appears to have been related. The Car- boniferous Arachnida comprise representatives of true spiders (Pro- tolycosa, Anthracomartus), scorpions (Koscorpius, Cyclophthalmus), and pseudo-scorpions (Microlabis). The scorpions appear to have attained a degree of specialisation very little below that of their modern representatives; but the true arachnids have all, or nearly all, segmented abdomens, and may be considered to mark a transi- tion between the arthrogastric and anarthrogastric forms. The Myriapoda, which have a solitary forerunner in the Devonian rocks of Scotland (Forfarshire), are represented by both the cheilognath- ous and cheilopodous types, although on account of certain structu- ral peculiarities the greater number of these earlier forms (Eupho- beria, Xylobius, Trichiulus) have been constituted into a special order, the Archipolypoda. Of the remaining invertebrate fauna of the Carboniferous period little need be said. The various groups of the tabulate and rugose corals (Lithostrotion, Syringopora, Cyathophyllum, Amplexus, Za- phrentis), the brachiopods, pteropods, lamellibranchs, gasteropods, and cephalopods, among the mollusks, and the crinoids and blas- toids (Actinocrinus, Platycrinus, Cyathocrinus, Dorycrinus, Batto- crinus, Pentremites, Granatocrinus) of the Echinodermata, have, as in the Devonian formation, abundant representatives; but they belong in considerable part to genera which now appear for the first time, or to such as had but a feeble development hereto- fore. The widely distributed group of trilobites, which, as has al- ready been seen, played such an important part in the faunas, of the Cambrian and Silurian periods, has here barely four gen- eric representatives, Phillipsia, Proetus, Griffithides, and Bra- chymetopus, whose species occur in the main part in the deposits situated below the true coal.* With these forms the trilobites disappear forever from the scene. While the deposits of the pre- ceding Silurian and Devonian formations have shown a fair repre- sentation of at least two of the primary groups of the Echinoder- mata, the Asteroidea and Crinoidea, especially of the latter, it is not until the present period that the urchins themselves (Echinoidea) acquire any significance (Archeocidaris, Palechinus, Melonites); * Professor Claypole has latterly announced the discovery of Dalmania in the ‘ Waverly group”? (Lower Carboniferous) of Ohio. * 152 GEOLOGICAL DISTRIBUTION. and here, also, for the first time, if we except the Laurentian rocks, with the hypothetical Eozoon, do the Foraminifera appear to enter largely as rock constituents. The genus Fusulina is developed to an extraordinary extent, and its distribution appears to be but little, if at all, less universal than that of the genera Nummulites and Orvitoides of the Eocene period. A solitary forerunner of the Nummulites has been discovered in the Carboniferous rocks of Belgium. In the remarkable development of the elasmobranch (shark) type of fishes, and in the absence of the bucklered ganoids, the Carboniferous ichthyic fauna is sharply defined from that of the Devonian. With the exception of a considerable number of fin- spines or ichthyodorulites, referred to such genera as Ctenacanthus, Gyracanthus, Oracanthus, &c., whose position is still very doubt- ful, and which may in part belong to the order of ganoids, all the remains of the former appear to have been more or less nearly related to the modern Port Jackson sharks. These remains are in the main in the form of teeth—Psammodus, Helodus, Orodus, Chomatodus, Petalodus, Cochliodus—whose (somewhat distant) resemblance to the pavement teeth of the cestracionts has led to their reference to members of that group ; not impossibly, how- ever, they represent a very distinct type.* The ganoids comprise, in addition to polypteroid forms—Ccelacanthus, Rhizodus, Megal- ichthys—representatives of the rhomb-plated Lepidosteidei, which include the American alligator-gar. The most widely distributed and most abundantly represented genera are Paleoniscus and Am- blypterus, the former of which is also one of the most abundant fishes of the succeeding Permian period. The only vertebrates other than fishes which appear in the Car- boniferous period, and now appear for the first time, are the Am- phibia, that group of animals whose members stand immediately next above the fishes in the scale of organisation, and whose em- bryonic forms are so clearly ichthyic as to have necessitated the union of the two classes into the one comprehensive division of the Ichthyopsida. It is not a little significant that the appearance of * Mr. Garman has recently described a species of shark from the Japanese seas, Chlamydoselachus anguineus, which appears to be generically most in- timately related to the Carboniferous Didymodus, and which, accordingly, rep- resents about the most ancient type among living vertebrates. CARBONIFEROUS FAUNA. 153 these animals should have been foreshadowed in the Devonian dip- teroid ganoids, which, leading up to the lung-fishes on one side, and not impossibly directly to the amphibians on the other, effect a transition to the higher class from the side of the fishes. This succession of higher upon lower types is not a matter of accident, but a direct outcome of the inevitable laws of evolution. Through the application of no other law would the numerous accidental or coincidental occurrences of direct succession, which present them- selves throughout the entire geological series, receive an intelligent explanation. All the Carboniferous amphibians belong to the ex- tinct order of the Labyrinthodontia (Stegocephala), salamandroids of both minute and gigantic frame, whose members were distin- guished by the possession of 2 dermal (cephalo-dorsal and ventral) armour of sculptured plates, and in many cases by a peculiar laby- rinthine infolding of the enamel of the teeth, a structure unknown among modern amphibians, but which is in great part shared by certain members of the ganoid fishes, as the modern alligator-gars (Lepidosteus) and the genus Rhizodus (Carboniferous). Among the genera are Anthracosaurus, Hylerpeton, Dendrerpeton, Batra- chiderpeton, and the cecilian-like Dolichosoma and Ophiderpeton. No other vertebrate higher in the scale of organisation than these Jabyrinthodonts is as yet apparent, unless, possibly, the very doubt- ful Eosaurus be proved to be a true reptile. The flora of this period partakes essentially of the character of that of the period preceding, the Devonian. We have here the same ancient representatives of the modern club-mosses and horse- tails, the Lepidodendra and their allies,* and the calamites, the ferns—Neuropteris, Pecopteris, Alethopteris, Sphenopteris, Cyclop- teris—giant tree-ferns, and forms that have been referred to the group of the cycads, an order of plants to which the sago-palms belong, and which appear to be not distantly removed from the conifers. No positive indications of the existence of any true flower-bearing herbaceous plants are yet manifest, and with their absence the total absence of flower-frequenting or nectar-sucking * The recent anatomical investigations of Renault and Saporta have led these authorities to consider Sigillaria, at least in some of its recognised forms, to be much more closely related to the gymnospermous phanerogams than to the club-mosses ; but Professor Williamson has pretty definitely shown that such a relationship does not exist. 154 GEOLOGICAL DISTRIBUTION. insects, the Lepidoptera and Hymenoptera, the two most highly organised orders of insects, is noticeable. The only true trees, or such as are made up principally of woody tissue, of the Carboni- ferous deposits belonged to the coniferous series, the order of plants which embraces the modern pine and its allies. These an- cient evergreens were represented by several distinct genera— Dadoxylon, Paleoxylon, Pinites—which, if the fossil fruit asso- ciated with their remains, and known as Lepidostrobus, be justly attributed to them, had their nearest allies among their modern congeners in the berry-bearing yews. No deciduous leaf-bearing trees, such as the oak, beech, or maple, which make up the great mass of our forest growths, can be positively shown to have existed in these early days. Permian Fauna.—In the formations of the period succeeding the Carboniferous, the Permian, a considerable advance in the structural type is indicated by the animal remains. While the predominant forms of life of the period preceding pass, although in most cases with very diminished numbers, into the present one —in fact, to such an extent as to have induced many geologists to unite the formations of the two periods into a common whole—we meet here with a class of animals whose representatives had not hitherto been detected. These are the true reptiles, most of whose members belonged to the order Theromorpha (Pelycosauria), rep- tilian forms which in several important characters—the structure of the pectoral and pelvic girdles, humerus, and tarsus—show strong affinities to the lower orders of mammals, the Monotremata and Edentata, of which, not impossibly, they may prove to be the early progenitors. A further approximation to mammalian structure is found in the character of the dentition, which in many forms ex- hibits a distinct differentiation into incisor and canine teeth. The deposits of the Southern and Western United States, especially of the State of Texas, have yielded a wealth of species and genera belonging to this order (Theropleura, Dimetrodon, Diadectes, Em- pedocles, Clepsydrops), representative of several distinct families. The modern type of lizards had their nearest analogues in the monitor-like Proterosaurus (Germany, England), whose dentition, however, was of the crocodilian type (thecodont). These early reptiles, while exhibiting many points of structure indicative of comparatively high specialisation, yet clearly proclaim a primitive PERMIAN FAUNA. 155 type of organisation in the rudimentary or embryonic condition of the vertebral column, which is in most cases only partially ossified. The Amphibia of the Permian period are by most authors placed in the single group of the Labyrinthodontia, although in certain structural departures from the normal type, as in the very rudi- mentary condition of the vertebral column, and in the absence of the peculiar labyrinthine infolding of the enamel of the teeth, some of the forms may have to be separated from this order. Most of the species were provided with a tail of greater or less length, and the general resemblance to living amphibians appears to have been mainly with the salamandoids, although in several points of struc- ture they more closely approximate the tailless frogs and toads. The relationship with the plated ganoids is well pronounced, and not improbably some of these, as dipneusts, or double breathers, may have been their true ancestors (as well as of the lung-fishes proper, Dipnoi). Among the more prominent genera are Branchio- saurus, Melanerpeton, Urocordylus, Archegosaurus, Eryops, Paleo- siren, and Ophiderpeton, the last two apparently apodal, and re- calling the cecilians in outline. In Eryops megacephalus, the largest of American amphibians, from the Permian of Texas, the skull measures eighteen inches in length and twelve inches in breadth. The fish-fauna of this period partakes essentially of the char- acter of the fauna: of the period preceding, from which it has borrowed most of its types. We have here, however, the first unequivocal remains of the genus Ceratodus (Bohemia and Texas), which represents the most ancient generic type of all existing Vertebrata. : Regarding the invertebrate fauna of the period, it may be re- marked that a deficiency in the number of forms is noticeable in nearly all the localities where the Permian deposits are developed, a circumstance due to the peculiar physical conditions under which the deposits were formed, and the subsequent alteration, resulting in the obliteration of the contained organic remains, to which, in many places, the rock-masses were subjected. A very large pro- portion of the known fossils are, as has already been intimated, of clearly Carboniferous types, more especially in the case of the Mollusca. The trilobites, so characteristic of the earlier deposits of the Paleozoic era, are wholly wanting, not a single individual, 156 GEOLOGICAL DISTRIBUTION. apparently, of this very numerous order having survived the Car- boniferous period. Here, also, we have the almost final disappear- ance of the two great groups of the rugose and tabulate corals, which by their numbers so eminently characterise the limestone deposits of the Paleozoic series, from the Silurian to its close. The Permian flora is essentially that of the Carboniferous period, and requires no special consideration. Paleozoic Faunas.—Briefly reviewing the more salient features of the Paleozoic faunas, we find, as far as the invertebrate series is concerned, that with few exceptions all of its recognised classes have their representatives, or, at least, there are representatives of nearly all those classes whose members could reasonably be expected to have been preserved in a fossil state. Thus, of the Protozoa we have the Foraminifera and Spongida; of the Ceelenterata, the Acti- nozoa and Hydrozoa; of the Echinodermata, the Echinoidea, Aste- roidea, Ophiuroidea, Crinoidea, Cystidea, and Blastoidea ; of the Mollusca (and Molluscoida), the Polyzoa, Brachiopoda, Acephala, Pteropoda, Gasteropoda, and Cephalopoda; and of the Articulata, the Crustacea, Arachnida, Myriapoda, and Insecta. Of the classes here enumeratedthere are wanting in the Cambrian the Actinozoa, * and possibly also the Hydrozoa; the Echinoidea, Blastoidea, and Ophiuroidea, among the echinoderms ; and the Arachnida, Myria- poda, and Insecta, among the articulates. In the Silurian the number of missing classes is reduced by six, since we have here representatives of both corals and hydroids, blastoids and brittle- tars, insects and arachnids; but the last two are represented almost by single individuals. In the Devonian the number is further re- duced by one, the class of the Myriapoda, likewise (as is also the case with the insects) represented in almost solitary individuals; only with the Carboniferous period do all the classes acquire for the first time any marked development. We thus cannot fail to remark the progressive evolution of new forms correlatively with the advance of time. Of the vertebrate series the Paleozoic deposits contain the remains of only three of the five recognised classes, the fishes, amphibians, and reptiles, which appear serially in the order of their progressive organisation, the lowest, or fishes, in the Silurian (or, if the conodonts be fishes, in the Cambrian), the amphibians in the Carboniferous, and the highest, or true reptiles, * Some forms have been doubtfully referred to this period in Scandinavia, TRIASSIC FAUNA. 157 in the Permian. These ancient deposits have as yet yielded no traces of either birds or mammals. Triassic Fauna.—lIn the first of the Mesozoic series of forma- tions, the Triassic, we enter, as it were, upon an entirely new phase of organic development. Many of the more characteristic groups of organisms of the preceding era have now either completely dis- appeared, or only survived in such diminished numbers as to con- stitute but a very insignificant element in the new fauna. Thus, of the class Brachiopoda but comparatively few of the older generic types are represented; and the same may be said of the other classes of mollusks, and more especially of the Cephalopoda. Of all the various forms of Paleozoic tetrabranchiates there are barely more than a half-dozen surviving types, and of these one, Orthoceras, itself becomes extinct in this period. But, in the place of these ancient types, we have others of the same class which are no less conspicu- ous for their numbers than for the complexity of form which they subsequently attain, and some of which exhibit a marked advance upon their predecessors in the scale of organisation. The ammo- nites, whose advent appears to have been foreshadowed in the goniatite and the Devonian Clymenia, now for the first time acquire any importance, and, indeed, if we except certain forms from the Carboniferous deposits of India and Texas—Arcestes, Xenodiscus, Sageceras, Medlicottia—now for the first time appear altogether. The numerous species which in some districts, more especially in the region of the Alps, crowd the deposits of this age, belong in principal part to the families Arcestide and Pinacocera- tide, as representatives of the leiostracous, or smooth-shelled divi- sion, and the Tropitide, Ceratitide, and Clydonitide (with the somewhat aberrant genera Cochloceras, Rhabdoceras, Choristoceras, and Clydonites), of the Trachyostraca, or forms with strongly sculp- tured shells. _ In these deposits, also, we meet in the Belemnitide with the first unequivocal traces of the dibranchiate or two-gilled, cephalopods, which, if we except the Nautilus, alone of this class of mollusks inhabit the seas of the present day.* The rugose and tabulate * The view entertained by several emincnt paleontologists, that the am- monites themselves represent dibranchiate forms, requires further support before it can be fully accepted. The evidence at the present time appears to be‘fully as much, if not more, opposcd to this notion as it is in favor of it. 158 GEOLOGICAL DISTRIBUTION. corals have been succeeded by the modern type of the star-corals, Zoantharia perforata and aporosa (Montlivaltia, Thecosmilia, Isas- trea, Thamnastrea, &c.), whose fragmentary remains build up giant reefs (Alps); and, similarly, the more distinctive ancient group of the Echinodermata, the crinoids, whose most characteristic repre- sentatives at this period are Encrinus and Pentacrinus, find their successors largely in the more modern Echinoidea, or true urchins (Cidaris, Hemicidaris, Hypodiadema). It is, however, in the vertebrate fauna that we find the most prominent feature separating the life of this period from that of any of the periods preceding. Not only do we meet here with the re- mains of fishes, amphibians, and reptiles, but with those of mam- mals, and not improbably also with the impressions or tracks of birds. Granting these last, which are, however, a little uncertain, it may be assumed that all the classes of the animal kingdom, as now recognised by naturalists, had their representatives. The fishes are still principally referable to the predominant type of the periods preceding, the ganoids, which also in a measure retain the embry- onic heterocercal tail, although a tendency towards homocercality is observable in some of the genera, as in Semionotus. The more numerously represented forms—Ischypterus, Catopterus, Semionotus —hbelong to the group typified in the American gar-fishes, and may be looked upon as the direct descendants of the Carboniferous and Permian Palzonisci. The lung-fishes find an abundant repre- sentation in the teeth of Ceratodus, which, as has already been seen, dates from the Permian, and possibly from a still older period. This animal furnishes us with one of those rare instances where a genus of living vertebrates has been founded upon the fossil remains. The amphibians of the Triassic period show but little advance over the type of their predecessors, all the forms still belong- ing to the single order Labyrinthodontia, some of whose members attained to prodigious dimensions (Mastodonsaurus, Labyrintho- don). To this group are probably referable the singular hand- shaped impressions of the animal known as Cheirotherium, or “hand-beast,” originally supposed to have been an animal of the frog-type, but now assumed to have been a salamandroid, or animal allied to the newts, and, like them, provided with a tail, although possessing in the structure of the skull certain features belonging TRIASSIC FAUNA. 159 to the tailless amphibians—frogs and toads. The true reptiles ex- hibit a remarkable variety of form, and, as in the succeeding Juras- sic and Cretaceous periods, constitute the most marked feature of the faunal remains that have been left to us. Hence, by some geologists the collective era of these three periods—the Triassic, Jurassic, and Cretaceous—or what is generally known as the Meso- zoic, has been designated the “era” or ‘tage of reptiles.” The modern lizards and crocodiles had both their ancient representa- tives, the former as indicated by the genera Telerpeton, Hypero- dapedon, and Rhynchosaurus, and the latter by Stagonolepis, Belo- don, and Parasuchus. But besides these there flourished a multi- tude of reptiles belonging to several distinct and very widely removed orders, which have left, to our knowledge, no traces whatever of their existence in the present seas. Such are the South African Anomodontia, some of whose members, as Oudenodon, were totally destitute of teeth, and had their beaks encased ‘in horn, after the fashion of the modern turtles (of which they may have been in part the progenitors); while others, as Dicynodon, possessed the horny mandibular apparatus of the former, but were provided, in addition, with a pair of huge and powerful teeth in the upper jaw;* the Theriodontia (as represented by the South African Galesaurus), reptiles whose dentition partook of the char- acter of that of the ordinary Carnivora, and whose earliest types had already appeared in the deposits of the Permian period; and the Plesiosauria, a group of essentially sea-inhabiting reptiles, which acquired a very considerable development in the Jurassic seas, and whose best known exponent is the Plesiosaurus. In the animals of this order the extremities of the limbs, both anterior and posterior, were encased in integument, and thus converted into flippers, very much like those of the whale, and admirably adapted for propul- sion through the water. The most characteristic genera of this period were Nothosaurus and Simosaurus. In Placodus the dental armature consisted in principal part of flattened plates, resembling the teeth of the pyenodont fishes, with which animals these reptiles were first confounded. * Professor Judd has quite recently (‘‘ Nature,’”’ October 15, 1885), an- nounced the discovery of dicynodont remains in the Elgin Trias of Scotland ; the group of animals had hitherto been known only from Africa, India and the Ural Mountains. 160 GEOLOGICAL DISTRIBUTION. The most remarkable of all the Triassic reptiles are the Dino- sauria, a group of the greatest importance when viewed from a tele- ological standpoint by reason of the many structural characters which separate them from the typical reptiles, and approximate them to birds. These avian characters are indicated principally in the structure of the powerful pelvic girdle and hind limbs, which depart very broadly from the normal type of reptilian structure. Thus, the pubic bones, in many cases, instead of projecting for- wards as in other reptiles, are directed backwards, more nearly parallel with the ischium, both bones therefore taking a position directed towards the posterior portion of the body, a feature char- acteristic of birds. In the hind limb, again, the ornithic char- acters are seen in the great cnemial ridge which is developed on the tibia, the gradual diminution of the fibula towards the distal extremity, the structure of the astragalus, and in the disposition of the digits, three or more, and their accompanying phalanges. The inner and outer digits are shorter than the rest, or quite rudi- mentary, and the third toe, as in birds in general, is the longest. There are good grounds for concluding that the bones of the limbs, and, doubtless, if this was the case, of some of the other portions of the trunk, were permeated with air-passages, as in birds. The structure of the fore limbs is still only imperfectly understood, but there is no doubt that in many cases they were but very feebly developed, being very much shorter. than the hind limbs, and that progression was, either habitually, or at least at times, effected by means of the posterior appendages alone. The remains of these earliest dinosaurs are indicated both by the actual parts pertaining to the skeleton (Zanclodon, Thecodontosaurus, Amphi- saurus, Clepsysaurus, Bathygnathus), and by the foot-prints, many of them three-toed, that have been left implanted in the rock- masses. Some of these, which measure fully a foot, or even con- siderably more, in length, were originally supposed to represent the imprints made by the feet of giant birds, a suspicion strengthened by the serial arrangement in twos in which the tracks are disposed; . but now that the structure of the dinosaurs has been more accu- rately determined, and their ornithic characters and mode of pro- gression recognised, there can be little doubt that they represent the imprints of the reptiles belonging to this order. This view is further strengthened by the circumstance that no actual remains of JURASSIC FAUNA. 161 birds have as yet been discovered in deposits of Triassic age.* But it is not impossible, or even improbable, that some of the smaller foot-prints that are scattered about the larger ones, and which in some instances are disposed in a single series one in advance of the other, indicating a method of progression adopted by certain wad- ing birds, may actually be of an ornithic nature. However this may be, it is certainly a significant fact bearing upon the doctrine of evolution, that no unequivocal traces of birds have thus far been discovered in deposits antedating those which contain the remains of reptiles, which in their several characters most approximate the birds, and in reality effect a transition to them. The progressive evolution of advanced or most specialised types is here clearly indicated. The Mammalia, the highest class of vertebrates, appear for the first time in the deposits of this age. They are indicated by the teeth and fragments of jaws pertaining to two or three genera, Dromatherium, Microlestes, and Hypsiprymnopsis, forms, as nearly as can be determined, belonging to the low type of the Marsupialia, and, probably, more or less closely allied to the modern banded ant-eater (Myrmecobius) and kangaroo-rats (Hypsiprymuus) of Aus- tralia. Jurassic Fauna,—The life-history of the Jurassic period, while combining certain prominent features not hitherto recognised, pre- sents to us primarily an expansion of those characters with which we have just become acquainted. The remarkable group of the dinosaurian reptiles, whose development in the Triassic period had but barely passed beyond its own beginnings, acquires here re- newed importance, apart from the mere matter of numbers, from the circumstance of the gigantic and diverse forms which it includes. Four distinct types of this order are recognised, all of which had representatives in the Jurassic period: 1. The Sauropoda, lizard- footed vegetable-eaters, in which the anterior and posterior pairs of limbs were of nearly equal length, and whose progression was effected on all fours. Among the more important genera of this period belonging to the group are Atlantosaurus, Brontosaurus, Morosaurus, and Cetiosaurus, the first, from the deposits of the *Since the above was written announcement has been made of the dis- covery of the skeletal remains of a track-making dinosaur of the Connecticut Valley. Travs., New York Ac. Sciences, Oct. 26, 1885. 12 162 GEOLOGICAL DISTRIBUTION. Rocky Mountains, measuring from eighty to one hundred feet in length—the largest land animal with which we are acquainted. 2. The Stegosauria (Stegosaurus, Scelidosaurus), armoured vegeta- ble-feeding dinosaurs, some of them of gigantic frame, whose pro- gression, owing to the feeble development of the anterior pair of limbs, appears to have been in great part effected by means of the hinder extremities alone. In Scelidosaurus Harrisoni, from the Lias of Dorsetshire, the hind foot measured three feet and a half in length. 8. The Ornithopoda, bird-footed herbivores, with a very unequal development of the anterior and posterior appendages, the latter closely approximating the structure found in birds. There can be but little question as to the habitually erect posture assumed by such forms as Camptonotus, Laosaurus, and Iguanodon. Iguanodon Mantelli, a Cretaceous species, measured about thirty feet in length from the tip of the nose to the extremity of the tail. No member of this genus is known from the American deposits. 4. The Theropoda, carnivore forms, whose progression was largely erect, and assisted in many cases, probably, by the greatly developed tail acting as a fulcrum, in the manner of that organ among the kangaroos. This type, which is almost alone represented in the Triassic deposits, includes the most formidable members of the order—Megalosaurus, Allosaurus, Dakosaurus, the former appar- ently attaining a length of fifty feet. The genus Compsogna- thus, represented by a single species (C. longipes) from the Upper Oolite, possesses probably the greatest number of ‘avian characters of the entire order, and is considered to stand in the direct line of the descent of birds. Monsters parallel to those of the land-surface inhabited the oceanic waters, such as the finned Plesiosaurus and Pliosaurus, and the not distantly removed Ichthyosaurus and its American tooth- less ally, Sauranodon. The geographical distribution of Ichthyo- saurus is a very remarkable one. While apparently the genus is completely wanting in the deposits of the New World, its range in the Eastern Hemisphere embraced very nearly its whole north and south extent, from Spitzbergen (Ichthyosaurus polaris, Triassic) to Australia (I. australis, Cretaceous). Its greatest development ap- pears to have been in the early part of this period (Lias). From the discovery of fragmentary parts of young individuals within the bodies of more fully developed ones, it has been conjectured that JURASSIC FAUNA. 163 the animal was viviparous, a supposition in a measure strengthened by the ill-adaptation of its structure to breeding on the land-surface. Not impossibly, however, these animals may have been in the habit of devouring their young, or the young of allied species, as it seems many species of snake do at the present day. In the Jurassic rocks we meet with the first traces of that ex- traordinary group of reptiles, the Pterosauria, which, in the pos- session of a tegumentary membrane stretched between the greatly elongated outer digit of the anterior limbs and the bases of the hinder extremities, resembling in many respects the flying-apparatus of bats, were enabled to navigate the air in the manner of birds. To these last, the pterodactyls, as the members of this order are familiarly designated, were closely related in the general conforma- tion of the skull, the pneumaticity of the bones, and the presence of a well-developed keel to the sternum or breast-plate, a character among recent animals found only in birds and bats. But while possessing these and other avian features, the pterodactyls depart in many important particulars from the bird type, and notably in the presence of true teeth implanted in sockets, as in the Croco- dilia, the structure of the manus, the absence of a feathery integu- ment—the animal having been apparently provided with a naked skin—and the possession of a tail composed of distinct vertebra.* Despite these important differences, however, it may, perhaps, be deemed doubtful whether the animals in question have not as much right to be considered birds as reptiles, the more so as the one great feature separating them from modern birds, the pres- ence of alveolar teeth, has recently been shown to be character- istic of some, if not of most, of the ancient birds. While, there- fore, it may not be possible to decide upon the exact position oc- cupied by these singular organisms, there can be but little doubt that they, or possibly some closely-allied predecessors with which we are not as yet acquainted, represent the primitive stock whence the type of the modern flying or carinate bird has been evolved. The birds would then have a double line of ancestry, the one here indicated, and another, culminating in the struthious or non-carinate * Professor Marsh has shown that at least in some forms of pterodactyls (Rhamphorhynchus) the extremity of the tail was provided with a tegu- mentary expansion, or vertical rudder, by means of which the animal doubt- less guided its flight. 164 GEOLOGICAL DISTRIBUTION. birds, having its origin in the dinosaurian reptiles, and in a form possibly not distantly removed from the Jurassic Compsognathus. The more important Jurassic genera of Pterosauria are Pterodacty- lus, Rhamphorhynchus, and Dimorpbodon, which differ from each other mainly in the character of the dentition and in the relative development of the tail. The deposits of this age have yielded, in addition to the reptilian forms mentioned, the remains of true lizards, crocodiles, and turtles. The first are but sparingly represented, and in the main, or wholly, belong to the acrodont division (Geosaurus, Acrosaurus, Homco- saurus, the last closely related to the modern Lacerta). The croco- diles, with some partial exceptions (Streptospondylus, Theriosuchus), belong to the primitive amphiccelous division (Teleosaurus, Mystrio- saurus), or those in which there is a retention of the ichthyic char- acter of bi-concave vertebra, as distinguished from the more modern forms dating from the Cretaceous period, with procclous (concavo- convex) vertebre. The turtles, which appear here for the first time, exhibit a remarkable differentiation, and in their diverse forms comprise representatives of several of the more important modern groups, as the Chelyde (Plesiochelys, Craspedochelys, Pleuroster- non), Emyde (Thalassemys), and Chelydridw. The recent genus Chelone is found in the Purbeck beds. The most interesting addition to the fauna of this period is fur- nished by the bird remains, whose earliest’ unequivocal traces are found in the famous Archeopteryx of the Solenhofen slates of South Germany (Bavaria), and in Laopteryx, from the deposits of Wyoming Territory—the last a bird probably of about the stature of a crane, but with uncertain affinities. The Archewopteryx, which is known by two more or less well-preserved specimens, and a feather pertaining to a third individual, combines in a most ex- traordinary manner what have generally been considered distinc- tively avian and reptilian characters, and, indeed, the animal may be regarded as a type intermediate between the two classes. Thus, in many points of structure of the skull and trunk, no less than in the structure of the tail, which was greatly elongated and made up -of numerous distinct vertebre, it is decidedly reptilian, and this relationship to the class of animals next lower in the scale of organ- isation is borne out by the discovery, recently made by Professor Dames, that the extremities of both jaws were provided with a num- JURASSIC FAUNA. 165 ber of diminutive teeth implanted in sockets. But, on the other hand, the animal, which was of about the size of a rook, was pro- vided with powerful wings, and these wings no longer consisted simply of a tegumentary membrane, as in the case of the bats and the extinct pterodactyls, but were made up of feathers as in living birds, a character indicating that the animal provided with them was warm-blooded. Feathers were also developed in pairs on either side of the tail; but the rest of the body, according to Vogt, appears to have been completely naked. The mammalian remains of the Jurassic period consist princi- pally of teeth and jaws, in a more or less complete state of pre- servation, whose characters indicate animals of diminutive size, pertaining wholly or in principal part to the order of the Marsu- pialia, or pouched animals. Both the insectivorous and the her- bivorous types had their representatives, the former in such genera, as Amphilestes, Phascolotherium, and Amphitherium, and the lat- ter in Plagiaulax; and it is not impossible that the more strictly carnivorous type of marsupial also then existed. Stereognathus, further, presents us with the type of a hoofed herbivore, and points to a possible origin of the modern placental ungulata. Thus, the marsupials had, as early as this period, attained a considerable de- gree of differentiation, though apparently less considerable than that exhibited by them at the present time. Latterly, some natu- ralists, and notably Professor Marsh, have attempted to show that these most ancient mammals of the Triassic and Jurassic periods were not true marsupials, as these are now recognised, but that they constitute distinct orders, Allotheria and Pantotheria, apart by themselves; there do not appear to be sufficient grounds, however, for the separation here proposed. In the invertebrate fauna of this period we see, even more than in the vertebrates, the reflection of the fauna of the period preced- ing, but with the predominant features very largely extended. These are in the main constituted by the mollusks, and more par- ticularly by the cephalopods, lamellibranchs, and gasteropods, the brachiopods (Rhynchonella, Spiriferina, Terebratula, Terebratella), although still sufficiently abundant, no longer having that para- mount importance which distinguished them as perhaps the most distinctive type of the Paleozoic faunas. The cephalopods still belong, in the main, to the types of the nautilus, ammonite (Amal- 166 GEOLOGICAL DISTRIBUTION. theus, Arietites, Harpoceras, igoceras, Stephanoceras, Lytoceras, Phylloceras), and belemnite ; but representatives of groups that appear to have been closely related to the modern calamary (Belo- teuthis, Belemnosepia, Teuthopsis) are not exactly wanting... The lamellibranchs and gasteropods comprise a most varied assemblage of forms, many of them but barely distinguishable from individual forms living at the present day, and by their great numerical de- velopment give a generally modern aspect to the fauna. Of the former the modern families Ostreide, Limidew, Mytilide, Astartide, Lucinida, and Cardiide are remarkable for their profuse develop- ment, and scarcely less so the now nearly extinct Trigoniade and Pholadomyida; of the latter, the more important families are still the non-siphonated ones (Pleurotomariide, Naticide, Trochide, Actwonidz); but a no inconsiderable representation of the Siphon- ata (Cerithiide, Aporrhaids, Strombidw, Purpuride) is also inter- spersed. The earliest fresh-water univalves belong to this period (Paludina, Melania, Neritina, Planorbis). The corals, which are of the type of existing star-corals, may be considered next in importance to the Mollusca, and, indeed, in some instances, as in the Coralline Oolite, they constitute by their own vast numbers the greater portion of the solid rock, not im- probably the vestiges of ancient reefs. Somewhat less important, but yet very abundant in certain localities, are the fragments of the Crinoidea, which are most distinctively represented by the genera Apiocrinus and Extracrinus, the latter having its modern analogue in the Pentacrinus of the Carribean Sea; but this comparatively little specialised group of the Echinodermata has, ever since the close of the Carboniferous period, been on its decline, and has left its place to be filled by the true urchins (Cidaris, Hemicidaris, Holectypus, Echinobrissus, Clypeus, Collyrites) and brittle-stars (Ophioderma, Ophiurella, Ophioglypha), both of which, but more particularly the former, now for the first time acquire any special importance. The star-fishes are represented, among other forms, by the type of the modern Uraster. Of the articulates there is a considerable development of the Crustacea—crabs, lobsters, and their allies—and in the fine-grained rocks the remains of centipedes, spiders, and true insects are not uncommon, the last comprising representatives of all the recognised modern orders. To this period belong the earliest Diptera, Hymenoptera, and Lepidoptera. JURASSIC FAUNA. 167 Turning to the flora, we find it to be sharply defined from that of any of the Paleozoic periods, although in the abundance of ferns, many of them of ancient type, and in the absence of the higher forms of plants, it shows an interesting correspondence. Its most marked feature is furnished by the group of the Cycads, of which there are numerous genera recognised, and the pines, whose nearest allies appear to be the southern araucarias. The earliest undoubted representatives of endogens are found in the deposits of this age, some of them clearly indicating a close relationship with the Aus- tralian screw-pines (Pandanus). No positive traces of exogenous plants other than conifers have as yet been determined, but it is by no means improbable that they already existed. -Comparing the fauna and flora of the Jurassic period with the existing fauna and flora of any portion of the earth’s surface, we remark a striking similarity to the conditions presented on the Australian continent. Here, at the present day, is the home of the marsupials, of the Port-Jackson shark, which had its Jurassic representatives in genera like Acrodus, Hybodus, and Strophodus, and of Ceratodus among the lung-fishes, a form which, though of more ancient date, also had its habitat in the seasof the Jurassic period. Only along the Australian coast do we meet at the present time with the lamellibranchiate genus Trigonia, one of the most characteristic and abundant of the Jurassic mollusks. As regards the flora, a no less striking correspondence is apparent. On the Australian land-surface flourish a considerable variety of ferns, tree- ferns, and cycadaceous plants; likewise, the Araucaria type of Conifer; and here, principally, do we find the singular plants al- ready referred to as screw-pines (Pandani). Australia is, in fact, that portion of the earth’s surface which, as far as its faunal and floral characteristics are concerned, has undergone the least modi- fication since the Jurassic period, and, indeed, it may be said that the present fauna and flora of the continent became differentiated during the interval between the Triassic and Jurassic periods, al- though, as has already been seen, some of the distinctive types date from a more ancient epoch. The retention of an ancient type of fauna and flora clearly indicates that the continent had retained its isolated position through a period probably extending as far back as the Mesozoic era; otherwise, if connection with some other continental land-mass had existed at some subsequent period, it 168 GEOLOGICAL DISTRIBUTION. would be barely possible that an interchange between the faunal and floral characters of that land-mass and Australia should not have been effected to a greater extent than is indicated by the isolated position, especially of the fauna, now existing. Cretaceous Fauna,—The Cretaceous period presents in many respects a marked contrast in its faunal characters to the period preceding. While many of the most important or characteristic of the Jurassic invertebrate types still persist, in many cases with undiminished or even increased force, as, for example, the differ- ent classes of the Mollusca, we meet here with a development of other animal groups which in most of the periods preceding were of comparatively insignificant import. Such are the Fora- minifera, which in their various forms (Globigerina, Rotalia, Tex- tularia, Cristellaria) build up by their remains the great mass of the chalk rocks, whose enormous extension is one of the most im- posing monuments presented to the geologist. The sponges (Si- phonia, Jerea, Thecosiphonia, Ventriculites) here likewise find their greatest development, some of the forms having their analogues in the types that still inhabit the oceanic depths; and the same has been shown to be the case with the Cretaceous urchins (Echinoidea), which are represented in great multitude and variety—Cidaris, Ananchytes, Galerites, Micraster, Discoidea. The corals are in comparison feebly developed, and can by no means claim that im- portance which they obtained in the Jurassic period. The Belem- nitide (Belemnites, Belemnitella) and Ammonitide still constitute the most important of the cephalopod types, the latter especially presenting a very considerable number of characteristic forms, the so-called unrolled ammonites—Crioceras (with Ancyloceras and Toxoceras), Hamites (Ptychoceras), Scaphites, Turrilites, Helico- ceras, and Baculites. The bivalve and univalve faunas, while largely made up of Jurassic types, show a marked advance over the corresponding faunas of the period preceding in the much greater development of the siphonate forms. The Sinuata among the former, which, if we except the very abundant family of the Pholadomyidz, had hitherto but scattered representatives, now acquire considerable importance, especially in the families Veneride, Tellinide, Glycimeridz, Ana- tinide, Mactride, and Myide. Among the non-sinuate forms the members of the oyster family (Ostrea, Exogyra, Gryphea) and CRETACEOUS FAUNA. 169 the scallops (Pecten), and the genvs Inoceramus among the Hetero- myaria, are distinguished by their numbers; but the most charac- teristic elements of the lamellibranch fauna are furnished by two families of very inequivalve-shelled mollusks, the Chamide, with the genera Requienia, Monopleura, Caprina, and Caprotina, and the so long misunderstood Rudistz (Spherulites, Radiolites, and Hippurites), whose forms so eminently characterise the southern belt of European and American Cretaceous deposits, and which ap- pear and disappear with this period. The siphonate univalves have an almost exclusively modern aspect, and comprise among others representatives of the families Fuside, Strombide, Muricide, Tri- tonide, Buccinidz, Cancellariide, Pleurotomide, Conide, Olivide, and Cypreide. Turning to the vertebrates, we find in the lowest class, Pisces, the introduction for the first time of teleosts, or true bony fishes, that ichthyic group which at the present day surpasses, both in individual members and variety, all the other orders of fishes put together. These earliest teleosts, although not very abundant, comprise a considerable number of modern types (Clupea, Esox, Osmerus, Beryx); but it is not till the Tertiary period that they acquire any well-marked development. No amphibian remains have been detected in any Cretaceous deposit. Reptiles, on the other hand, are exceedingly abundant, and comprise most of the types whose existence has been indicated in the Jurassic seas. Thus, of the modern groups, we have turtles, lizards, and croco- diles (of both the amphiccelous—Hyposaurus—and proccelous types —Holops, Gavialis), and, in addition, the first true serpent (Si- moliophis). The extinct orders Ichthyosauria and Plesiosauria are still represented, and in Elasmosaurus, belonging to the lat- ter, we meet with one of the most formidable types of the finned Reptilia. Here, also, are found some of the most gigantic of the Dinosauria—Iguanodon, Megalosaurus, Hadrosaurus, Camarasau- rus—and the remarkable group of the Pythonomorpha, or ‘“sea- serpents ’—Mosasaurus, Leiodon, Clidastes—which in several re- spects united the characters of both serpents and lizards. The largest of the pterodactyls, or flying reptiles, having an expanse of wing of from twenty to twenty-five feet, or even more, occur in deposits of this periol, and are represented by the normal- toothed types, and by such, as the American Pteranodon, in which 170 GEOLOGICAL DISTRIBUTION. the jaws appear to have been encased in horn, and to have been entirely edentulous. Bird remains are sufficiently abundant in certain localities, many of them belonging to forms seemingly not very far removed from some of our modern groups. But, in addition to these ordinary forms, we have some of the most extraordinary of any that have ever been described, and which, from the presence of true teeth in their jaws, have received the name of Odontornithes (toothed-birds). In the genus Ichthyornis, as exemplified in I. dispar, which was of about the size of a pigeon, in addition to the peculiarity of alve- olar teeth that of biconcave vertebre is presented, a structure of the vertebral column characteristic of fishes and many of the ex- tinct reptiles, but not known in modern birds. The wings ap- pear to have been well developed, and in this, and all other respects beyond those just mentioned, the animal conformed strictly to the modern type of bird structure. In the still more remarkable Hes- perornis, which in the species H. regalis attained » height of five or six feet, the teeth, instead of being implanted in distinct sockcts, were placed in a continuous groove; the extremity of the upper jaw appears to have been bent down in the form of a beak, and to have been edentulous. The breastplate was entircly destitute of a keel or ridge for the attachment of the powerful muscles required for the motion of the wings, so that the bird was doubtless completely do- nied the power of flight. The presence, in the same geological period and the same geographical area (Kansas), of two birds so closely related to each other in the presence of jaw-teeth, nnd yet so distantly removed from each other by other peculiarities of structure, argues strongly for the antiquity of this class of animals, and, though the earliest unequivocal traces of birds have thus far been met with in the deposits of the Jurassic period, it is more than probable that their first origin is considerably more ancient. No traces of any mammalian have thus far been discovered in any indisputably Cretaceous dcposit, a circumstance in great part attributable to the particular conditions under which most of the deposits of this period, as known to us, were laid down, namely, their marine origin. But there can be no doubt that at some future day such remains will be found, and, indeed, if the deposits of the Laramie age be conceded to be absolutely Cretaceous, as is claimed (although on most contradictory evidencc) by many geologists, then CRETACEOUS FAUNA. 171 the first of such remains, the Meniscoessus, has quite recently been discovered. As now generally recognised, the Laramie deposits constitute a series intermediate between the Cretaceous and the Tertiary, the faunal characters, as are principally indicated by the abundant remains of dinosaurian reptiles, pertaining to the former, while the plants point directly to the latter. The angiospermous exogens, whose earliest undoubted remains occur in the Upper Cretaceous deposits, here undergo a very considerable develop- ment, and may, indeed, be said to represent the stock whence the floras of the subsequent Tertiary and existing periods have been derived. We find here many of our most common modern types, such as the oak, beech, poplar, tulip-tree, magnolia, alder, and plane. Tertiary Faunas.—With the close of the Cretaceous period and the beginning of the Tertiary, we note the most marked of all the organic changes that characterise the different geological epochs. Whole series of animals, from the lowest almost to their highest di- visions, suddenly become extinct, or so nearly verge on extinction as to constitute but a very insignificant element in the succeeding fauna; on the other hand, groups of equal or greater importance, and which had hitherto no (or but very scanty) predecessors, just as suddenly make their appearance. It would seem as though a fresh start had been taken in the peopling of the earth’s surface, so different in many respects are the faunas of the Cretaceous and Tertiary periods. But this difference, as it now presents itself, must not be taken to indicate that it in fact even existed as such. The gaps that now separate the one fauna from the other were un- doubtedly filled by animal types of intermediate grade, of whose existence we shall only be made cognisant when the hiatus which here breaks into the continuity of the geological system will be more completely filled in. It is illogical, and directly opposed to the workings of evolutionary force, to conceive of a wide-spread group of animals suddenly appearing and springing into prominence ; and no less illogical to conceive of an equally sudden extermina- tion. Hence, where vast differences in the faunas of any two suc- ceeding geological periods present themselves, we have reasonable grounds for concluding that a long lapse of time has intervened between the close of one period and the commencement of the period (as represented) next succeeding—in other words, that there 172 GEOLOGICAL DISTRIBUTION. is here a geological break. Only there where the continuity of the geological system is complete, or where the imperfection of the record is reduced to insignificance, can we hope to meet with an organic chain whose continuity is likewise complete. No such complete record, or anything approaching it, has as yet been dis- covered, nor is it at all likely that one will ever be discovered. But the gaps in the record that occur in one locality or country may be wanting in another, those present here be absent in the third, and so on; hence, by a series of comparisons made between several localities, we can in a measure realise a comparatively perfect record, or at any rate one in which the breaks have been materially narrowed, and with it also a comparatively perfect organic chain. Except possibly in one or two regions of the earth’s surface, New Zealand and California, nothing that may be said absolutely to link together the Cretaceous and Tertiary deposits, at least those of the marine series, has as yet come to light; the faunas are largely distinct, and their distinctness is the index of the inter- val that separates the outgoing of the one and the incoming of the other. The Tertiary fauna presents to us a clearly modern aspect, and one that characterises all the animal groups represented, from the lowest to the highest. And the farther we advance in this period the more modern becomes the general faunal facies, so that in the Pliocene, or uppermost division, not only are the genera largely identical with existing ones, but (if we exclude the vertebrates) also the species, notably among the mollusks. It may be stated in a general way that all the more comprehensive of the animal groups now existing are represented in the Tertiary deposits, and the majority of these date from the Eocene, or earliest division. We have no longer representatives of those wonderful reptilian orders, the Ichthyosauria, Dinosauria, Pythonomorpha, and Pterosauria, which characterised the greater portion of the Mesozoic era, and continued to its termination; nor do we find any vestiges of the scarcely less wonderful birds of the odontornithic group,* or of the type rep- resented by Archeopteryx. Both reptiles and birds belong to * An exception may, perhaps, be made in favour of the Odontopteryx, de- scribed by Professor Owen, which has the substance of both jaws developed into well-pronounced serrations (or false teeth), an exaggeration of the character exhibited by ducks and geese, to which the bird appears to bave been related. TERTIARY MAMMALIA. 173 the type of existing orders, and the same may be said of the fishes, principally teleosts. The change in the character of the inverte- brate fauna is somewhat less marked than in the case of the verte- brates; but yet certain important differences present themselves. Thus, among the acephalous and gasteropod mollusks, by far the greater number, in fact nearly all the types, are referable to exist- ing families, and even in the oldest division, the Eocene, to exist- ing genera, or to such as are very closely allied to them. Such characteristic families as the Hippuritide and Caprotinide, among the bivalves, have completely disappeared, and, if we except some half-dozen or more species found in Australian Tertiary deposits, the same may be said of the Trigoniade, as well as of the Am- monitide * and Belemnitide among cephalopods, about the most distinctive of the invertebrate forms of the entire Mesozoic series. Among the Tertiary invertebrates must be noted the extraordinary development of the foraminiferal forms Nummulites and Orbitoides, which, by their prodigious numbers, make up some of the most stupendous deposits known to us. But that feature of the Ter- tiary fauna which above all others arrests attention is constituted by the class Mammalia. The most striking fact that presents itself in connection with the history of these animals is their very sudden introduction, both as to individual numbers and diversity of form, almost with the beginning of the period, a circumstance of no little significance when it is remembered that, in the period preceding, if we except the doubtfully placed Meniscoessus, not even a trace of their existence has been detected, and that all such forms as have been found in the earlier Jurassic and Triassic deposits belong, as far as we are able to determine, to the single order of the Marsupialia. In the earliest division of the Tertiary, the Eocene, on the other hand, we meet with the remains of individuals belonging to at least one- half of all the recognised orders of the present day.t Thys, we have marsupials of the opossum type (Didelphis), insectivores, rodents (as represented by the Sciuride, or squirrels), cetaceans * A few ammonitic fragments have been found in the Tertiary deposits of the Tejon group of California, and a Tertiary belemnite is claimed for Aus- tralia. + The Ornithodelphia, Edentata, Proboscidea, Hyracoidea, and possibly also the Sirenia and true Carnivora, are still unknown, 174 GEOLOGICAL DISTRIBUTION. (Zeuglodon), ungulates, both odd-toed and even-toed (among the former the tapiroid Lophiodon and Palwotherium, and other such forms as Eohippus and Hyracotherium, which, through a series of modified but closely-related types in the Miocene and Pliocene peri- ods—Anchitherium, Hipparion—can be traced genetically to the modern horse; and among the latter the possible ancestors of some of the modern deer, Xiphodon and Anoplotherium, and the suil- line Anthracotherium and Paleocherus), bats, even of existing gene- ra (Vespertilio, Vesperugo), lemurs, or lemuriform insectivores (Ada- pis, Necrolemur), and not impossibly also the true monkeys. But while most of the forms found in these earlier Tertiary deposits are referable to modern orders, there are others which would appear to have no place in the classification laid down for living forms, and which combine, in many respects, the characters of two or more orders. Thus, it has been convenient to designate an order Ambly- poda for a line of animals which, at the one extremity, stand near- est in their relationship to the Proboscidea, or elephants, and at an- other to the odd-toed ungulates. In it are comprised the Uinta- theria, ponderous tusked-animals, rivalling or exceeding in size the modern elephant, and the coryphodons, considerably smaller ani- mals of a generalised type, the probable progenitors of the last. A still earlier type is embodied in the Condylarthra (Phenacodus), from the very base of the Eocene, which represent the most primi- tive type of known ungulate animals, and which not impossibly are derivatives of some-preceding hoofed marsupial. Another order, the Tillodontia, has been established for certain animal forms which, in several respects, combine the characters of the insectivores, ro- dents, and edentates; and, again, a fourth order, the Creodonta, for forms that seem to hold a position intermediate between the insectivores and carnivores, and not unlikely represent the ancestral line of the latter. From the researches of paleontologists it would appear that the primitive type of placental mammal is the insectivore, and that from this original type have descended, by gradual modifica- tion, most of the varied forms that now people the surface of the earth, and those whose remains lie buried in the deposits of the Tertiary period. At what precise period in the earth’s history the Insectivora first appeared it is impossible to say, for, although no remains occur in any deposits antedating the Eocene, there can be TERTIARY MAMMALIA. 1%5 little or no doubt, seeing what modifications of insectivore structure are presented in the earliest deposits containing their remains, that they appeared at a very much earlier epoch. The Tillodontia, Creodonta, and Insectivora appear, as it were, simultaneously in the Lower Eocene deposits, and if, therefore, they represent merely modifications of one and the same structure, as is maintained by Professor Cope, who has united the three groups into the one com- prehensive order of the Bunotheria, then they must point to a com- mon progenitor (foreshadowed in the Jurassic insectivorous marsu- pials) removed far beyond the limits of the Tertiary period. Of the three insectivore types here indicated, the true Insectivora, which may be considered as the main or axial stem, have alone survived to the present time. The Tillodontia and Creodonta both became extinct before the middle of the Tertiary period, the latter, however, by gradual modification passing off into the Carnivora, whose earliest undoubted remains are to be found in the deposits of Oligocene, or Miocene age. From the same group of the Insec- tivora, although apparently at a somewhat later date than the Creo- donta and Tillodontia, appear to have been descended the so-called Prosimia, or primitive monkeys, the lemurs, whose earliest remains occur in deposits of both Lower and Upper Eocene age; and to these last, again, is doubtless to be traced the direct line of ancestry of the various types of true monkeys that at the present day inhabit the earth’s surface, and whose unquestionable traces are first met with in deposits of Miocene age. The most important non-insectivore type of Lower Eocene mammalian is the ungulate, whose remains, be- longing to both the odd-toed and even-toed sub-orders, occur in astonishing abundance, and argue very strongly in favor of a very remote ancestory, one that may not impossibly carry us as far back as the middle of the Mesozoic era. The progressive modifications of structure which can be traced through the more generalised of the Eocene mammalian groups results in greater and greater specialisation the further we advance in the course of time, and hence, in the Miocene period we meet with more of distinctly specialised (or isolated) groups than in the period preceding. In addition to the recent orders that have been enumerated as belonging to the Eocene period we have the Eden- tata (represented by such gigantic forms as Macrotherium and Ancylotherium, whose nearest relationship appears to have been 1%6 GEOLOGICAL DISTRIBUTION. with the aard-vark), the true Carnivora, Sirenia,* Rroboscidea, and Quadrumana. Per contra, most of the older forms have now com- pletely disappeared, and, in fact, no mammalian order, with the possible exception of the Creodonta (Hyzenodon), is indicated which has not its living representatives at the present day. Most of the % g : <= & > é Xe pO g a PLIOCENE MIOCENE A (O-LLGO-CENE) CREODONTA \ TILLODONTIA EOCENE BUNOTHERIA CRETACEOUS P DIAGRAM ILLUSTRATING RELATIONSHIP OF TERTIARY MAMMALIA. families are such as still exist, and even many of the genera are identical, so that on the whole the mammalian fauna has a decidedly modern aspect. The Miocene Insectivora comprise, among other forms, representatives of the families of hedgehogs, shrew-mice, and moles; the Rodentia, porcupines, mice, squirrels, rabbits, beav- ers, &c.; the Cetacea are represented by true whales and dolphins; the odd-toed Ungulata by the tapir and a number of allied tapir- oids, and the singular giant forms that have been referred to the not distantly removed family of the Menodontide (Symborodon, Titanotherium); by true rhinoceroses and other forms (Hyracodon, Aceratherium) closely allied to them; and by Equidx—Hipparion, Miohippus (Anchitherium)—which differed from the true horses * Eotherium Egyptiacum, from the Mokattam nummulitic limestone, is re- ferred to this group by Professor Owen. TERTIARY MAMMALIA. 177 principally in size and the polydacty] character of the feet. Among the even-toed ungulates we find the hippopotamus, the true swine, deer, giraffe, and musk-deer, and, of the hollow-horned ruminants, the antelopes—the sheep, goats,* and oxen being still absent, al- though some of the antelopine forms would seem to effect a transition between the true antelopes and goats. The Proboscidea comprise, in addition to the true elephant (which, however, as a Miocene ani- mal is known only from the deposits of the Siwalik Hills of India, now frequently referred to the Lower Pliocene, or Mio-Pliocene), the Mastodon, and the aberrant Dinotherium, which was provided in its lower jaw with two prominent recurved tusks. The Carnivora have yielded representatives of the cats—the true Felis and the related sabre-tooths (Machairodus, Dinictis), the most formidable of all known recent and extinct Carnivora—the weasels, civets, hyenas (with the true hyena), and seals. The dogs are represented by the genus Canis itself, and the more primitive Amphicyon, through which a transition is effected to the ursine Hyzenarctos, and to the Pliocene true bears. Finally, the Primates have yielded several genera, as Semnopithecus, Pliopithecus, and Dryopithecus, the last referable to the group of the anthropoid or highest apes, and fully equalling in size the human species. Passing on to the Pliocene period, the mammalian fauna makes a still further approximation to that of the present day in the in- troduction of a number of modern types that had not hitherto made their appearance, or only just appeared. Thus, we have here the camel (in India), the ox, true bear (in Europe), and horse, in addi- tion to most of the types that have been enumerated as belonging to the Miocene period, and it may be broadly stated that the ma- jority of the genera of this period are such as still exist, although the species are in most cases distinct. The regions where Tertiary mammals have been studied are principally the United States, Eu- rope, and India, between whose faunas there is a well-marked cor- respondence. While certain of the animal groups referred to are found in the one region and not in the other, and are therefore specially restricted, it may be said that approximately the same groups are represented throughout, although the date of their ap- pearance, or of that of their individual components, may be different for the different countries. Thus, in the Upper Miocene, or older * Capra Perimensis, from the island of Perim, is possibly a Miocene form, 13 178 GEOLOGICAL DISTRIBUTION. Pliocene, deposits of the Siwalik Hills of India we have the true hippopotamus, bison, bear, and elephant, forms which do not make their appearance until a somewhat later date in Western Europe, Pliocene, or Post-Pliocene. Similarly, the genera Cervus, Hystrix, Felis, Hipparion, and Mastodon, which appear in Western Europe in the Miocene period, are still wanting in the American continent, making their first appearance in the Pliocene. And, likewise, the true bears and oxen in Europe antedate the American forms by one period. It may be stated, as a general rule, that where identical genera of living forms occur in the deposits of both the Old and the New World, those of the Old World are the more ancient; and the same probably holds good, although to a less extent, with families. From these differences in the dates of appearance of certain animal groups, their presence or absence, we are led to discuss the probable origin of our existing faunas, or portions of them. The existence in Western Europe in Miocene, and especially in Pliocene, times of a fauna consisting of forms which still inhabit the region, and of others as are only to be found at the present time on the continents of Africa and Asia, may appear at first sight somewhat singular. But when we reflect that the climate, during the whole or the greater portion of this period, was probably very much more uniform and warmer than it is at the present time, and possibly not very different from what it now is in the region of the Tropics, the apparent singularity in great measure disappears. Some of the tropical forms, as the giraffe and rhinoceros, may have been indigenous to the region, while others, whose development in South-Central Asia appears to have taken place at an earlier period, not improbably represent immigrants from the heart of that con- tinent. It is practically certain, moreover, that direct land commu- nication existed during a considerable portion of this period with the continent of Africa, with which, consequently, there would have been effected a general interchange of forms. Indeed, it is much more singular that Europe no longer retains its more charac- teristic African forms; but it must be recollected that, with the advent of the Glacial period, an era of cold set in, and that with this inclement climate a general retreat southward took place, the more tropically constituted animals passing over into the conti- nent of Africa, or suffering extermination by the cold. The most northerly animals, passing southward, occupied the region now more ORIGIN OF EXISTING FAUNAS. 179 or less vacated by the tropical forms, and hence, in the deposits of the Glacial and Post-Glacial periods, we meet with the remains of the elk, reindeer, hyena, lion, giraffe, elephant, rhinoceros, and hippopotamus mixed together. At about the same epoch it would appear that the present rupture existing between the African and European continents was effected, a separation which precluded the possibility of a return migration from Africa when the more toler- able climate succeeding the close of the Glacial period set in. Hence the survival only of the more temperate forms of the Euro- pean fauna. While Africa, therefore, retains its strictly African mammalian forms, it may be considered questionable whether these are not-direct importations, in great part, from the region lying to the north. As far as the North American continent is concerned, it appears not improbable, from what has already been said with refer- ence to the earlier appearance in Europe of equivalent mammalian types, that a not inconsiderable portion of its later (fossil) fauna was derived from the Old World. Thus, it appears likely that the bears, swine, oxen, sheep, antelopes, and elephants criginated in the Old World, whence they were transplanted by way of some land connection existing in the north into the New World. The true dogs, on the other hand, seem not unlikely to have been de- veloped first on the American continent; and it is also not improb- able that the ancestral line of the camel is to be traced to the West- ern Hemisphere. Our paleontological knowledge of the different countries, even of those more thoroughly explored, is, however, far too insignificant to permit of a definite solution to the problem of the origination of the various mammalian groups, and in the case of most continental faunas but little can be said with positiveness concerning their formation. The North American continent lacks in its Tertiary fauna the giraffe, hyena, and hippopotamus; nor do we find any traces of the group of the Old World monkeys, or, in the greater portion of the region, of the Edentata, whose various forms are now so abundantly represented in the South American fauna. With the Post-Pliocene period the correspondence existing be- tween the fossil and recent faunas of the several geographical regions is in most cases further increased, and not only by the introduction of many new modern genera, but by the presence, in considerable number, of identical specific types. The modern fauna may now 180 GEOLOGICAL DISTRIBUTION. be said to be broadly marked out. Thus, in the Australian Pleis- tocene marsupials, Diprotodon, Nototherium, Thylacoleo, and their allies, we have the forerunners of the various marsupial forms that now characterise the continental fauna; in the giant birds Palapte- ryx, Dinornis, Mionornis, &c., from New Zealand, and Apyornis from Madagascar, the forerunners of the wingless apteryx and the struthious birds from the same or neighbouring regions; and in the giant South American edentates, Glyptodon, Megatherium, My- lodon,* and their allies, the representative, if not the ancestral, forms of the existing sloth, armadillo, and ant-eater. It is re- markable that these last forms also occur in the Post-Pliocene de- posits of the United States; but there can be but little doubt that their presence there was the result of a temporary migration from the south, since their remains are only exceptionally found in any of the preceding Tertiary formations. We have noted in the Eocene period the presence of a certain generalised group of mammals, from which, by gradual modifica- tions of structure, the more specialised groups of subsequent periods have sprung. The demonstration of this successive evolution of forms is not, however, restricted solely to groups of animals, but it can be indicated with no less positiveness in the case of certain in- dividual members of a group. The most notable instance of evolu- tionary modification in a given line is afforded by the horse. Thus, from the modern horse we can trace downward in the geological scale a gradual series of modifications in the structure of the teeth and limbs which, at the further end of the line, characterise an animal so far removed in general structure from the existing form that, were not the intermediate forms known, or were it to be con- sidered by itself, it would be recognised not only as the type of a distinct family, but of a distinct sub-order. From the solidungu- late type represented in the existing form we reach, by sensible gradations, an animal of the polydactyl type, or one having several toes to each foot. A phylogenetic line, but little less complete, can also be traced in connection with the families Camelidw, Tapiride, and .Felide, and others, doubtless, will be discerned with the fur- ther progress of paleontological investigation. * The deposits containing these remains have been very generally consid- ered to be Post-Pliocene; Ameghino and Cope, however, probably correctly refer them either in whole, or in part, to the Pliocene. II. Appearance and disappearance of species.—Reappearance. —Extinction.—Per- sistence of type-structures.—Variation.—Geographical distribution.—Cli- matic zones.—Synchronism of geological formations. Ir is assumed by all, or nearly all, geologists, that every species of animal, broadly speaking, had a definite belonging in the geo- logical scale; in other words, that its existence was coincident with a certain period in the development of the earth, and with no other. Thus, the well-known and largely-represented brachiopod, Spirifer disjuncta (Verneuilii), whose occurrence has been noted in North America, throughout the greater extent of continental and insular Europe, in Asia Minor, China, and New South Wales, is everywhere restricted to the Devonian formation, and is, therefore, distinctive of that period. Similarly, the no less widely disseminated Pro- ductus semireticulatus, a member of the same group of animals, is restricted to the Carboniferous formation. So limited, indeed, ap- pears to have been, in most instances, the range in time of a given species, that the inspection of a single well-determined form will frequently fix, not only approximately but absolutely, the horizon of the deposits whence it was obtained. Belemnitella mucronata, one of the squids, characterises a definite horizon of the Upper Cretaceous; and among the Ammonites we have numerous instances of specific restriction to special “zones” of even the minor divi- sions of a formation. Limitation of range appears to pertain more strictly to the members of the higher groups of animals than to the lower, or to such forms whose complexity of organisation might be supposed to interfere with a ready ‘accommodation to changing physical conditions of the surroundings. Not one of about one hundred and twenty-five species of fish described from 182 GEOLOGICAL DISTRIBUTION. the Old Red Sandstone of Great Britain appears to have lived on into the succeeding Carboniferous period, whereas, of the Inverte- brata, comprising the corals, annelids, echinoderms, crustaceans, and the several classes of the Mollusca, the survivors of the Devo- nian period number no less than twelve per cent. An equally striking case is presented by the Mammalia, where, of the very numerous forms that have been referred to the European and North American Tertiaries, not one is positively known to have passed either from the Eocene division to the Miocene or from the Mio- cene to the Pliocene; and but a mere handful, if that, from the Plio- cene to the period next succeeding, the Quaternary or Post-Plio- cene. And yet we are aware that, in certain Eocene localities, no less than five per cent. of the molluscan fauna has survived into the present epoch, and as much as thirty to forty per cent. from the Miocene! Turning to the Invertebrata themselves, we find among the different classes no less striking confirmation of the law of the persistence of the less highly organised specific types over those more highly organised. Taking the sub-kingdom Mollusca, for example, we find, from an examination of the carefully prepared tables of Mr. Etheridge ® on British Paleozoic fossils, that, of the three great classes whose members are not free-swimmers, and who ’ would be consequently most likely to fall under the influence of special physical conditions, the order of persistence is, in most cases, Brachiopoda, Lamellibranchiata, and Gasteropoda—d. ¢., the lowest first and highest last. Species of brachiopods range from every one of the major formations to the formation next succeed- ing, as from the Cambrian to the Silurian, from the Silurian to the Devonian, from the Devonian to the Carboniferous, and from the Carboniferous to the Permian. The Lamellibranchiata and Gasteropoda, on the other hand, each pass but once from the De- vonian to the Carboniferous. Looking at the numerical develop- ment of the transgressional forms, we find that fourteen per cent. of the Devonian brachiopod fauna reappears in the Carboniferous, thirteen per cent. of the lamellibranch, and eleven per cent. of the gasteropod. Of the equivalent polyzoan fauna the transgres- sional forms constitute thirty-seven per cent. Numerous instances of transgressional forms could be cited from the other branches of the animal kingdom, but to no special pur- pose. As a rule, the number of such connecting forms is very REAPPEARANCE OF SPECIES. 183 limited, and only in the comparatively very recent Tertiary epoch do they acquire any marked significance. But, if the number of survivors of any one epoch is very limited, it will naturally follow that this number will be still further reduced if a question of two or more epochs is involved. It was, indeed, for a long time main- tained by geologists that no species of animal, no matter of what form of organisation, could possibly have entered into the forma- tion of three successive [epoch] faunas; for instance, that no species appearing in the Silurian could live completely through the Devo- nian, and then continue into the Carboniferous. And this notion is still largely entertained by the geologists and paleontologists of the present day. However much of truth there may be in such a doctrine, it must be confessed that its acceptance or rejection will depend, at least in some part, upon the standpoint from which the investigator views the nature of species. There is, perhaps, nothing that has more taxed the ingenuity of the naturalist than to deter- mine just exactly what a species is, what constitutes its absolute boundaries or limitations. The amount of disagreement upon this point is so very great, even among naturalists holding approximately the same views on genesis or evolution, that one might fairly despair of arriving at anything like a just solution of the problem. During the period when the doctrine of the immutability of species was a common faith, there was, indeed, but little difficulty in the matter, since every reasonably differing form was immediately constitut- ed into a distinct species; and it is in this period that many, if not most, of our existing paleontological notions have their roots. Now, however, when the doctrine of descent by modification is universally acknowledged as one of the great truths of nature, much greater latitude is permitted to the definition of the word species, and, in fact, what might at one time be considered as a good species can, in the light of a newly-discovered chain of “ intermediate ” forms, be readily degraded to the rank of a variety. Such has, in truth, been the history of a great many so-called species. The difficulty of determining specific longevity thus becomes apparent, for who can state what will be the fate of forms that now stand apparently far apart? However divergent may be the views of authors on the matter of relationship, it is practically certain that numerous forms of life, exhibiting no distinctive characters of their own, are constituted into distinct species for no other reascn than 184 GEOLOGICAL DISTRIBUTION. that they occur in formations widely separated from those holding their nearest of kin. Whether these be really good species or not may be a matter for further consideration; but it cannot be denied that their primary recognition as such is based upon the assumption that no species, after it once became extinct, ever again came into existence. While there is much that speaks in favor of this doc- trine, it may, nevertheless, safely be asked, in what lies the proof of its correctness? Surely we possess no knowledge which will permit us to state just when a given species became extinct. Dis- appearance from one locality is in itself no indication of absolute extinction, any more than appearance is an indication of primary origination. How, then, can we ascertain, when a given form supposed to be extinct reappears after an interval of a formation, whether that form in reality became extinct or not? It is usually assumed that it did not, and its range in time is correspondingly extended; or, the reappearing form, with no distinctive characters of its own, is elevated to the rank of a new species, and the extinc- tion of the first species insisted upon. But it is evident that this method of forcing the point is in the nature of an argumentum in circo, and leaves the question of extinction and reappearance in the condition of ‘‘not proven.” While, apart from the proof that is lacking in the matter, the doctrine of non-reappearance seems to commend itself by a certain “plausibility,” it may still be doubted whether this supposed plausibility is not more a matter of preconception than of actual fact. If evolution is true, and there are few among scientists who would deny that it is so, can it not readily be conceived that, as the result of the interaction of the physical and organic forces, identical forms may have been evolved as the heads of very distinct lines of descent? And, if so, may not this process have operated through distinct periods of time? Mr. Darwin, in attacking the problem, thus states the case (“Origin of Species,” p. 379, ed. 1866): “‘ We can clearly understand why a species, when once lost, should never reappear, even if the very same conditions of life, organic and inorganic, should recur. For though the offspring of one species might be adapted (and no doubt this has occurred in innumerable instances) to fill the exact place of another species in the economy of nature, and thus supplant it, yet the two forms— the old and the new—would not be identically the same, for both REAPPEARANCE OF SPECIES. 185 would almost certainly inherit different characters from their dis- tinct progenitors. For instance, it is just possible, if our fantail pigeons were all destroyed, that fanciers, by striving during long ages for the same object, might make a new breed hardly distin- guishable from our present fantail; but, if the parent rock-pigeon were also destroyed, and in nature we have every reason to believe that the parent-form will generally be supplanted and exterminated by its improved offspring, it is quite incredible that a fantail, iden- tical with the existing breed, could be raised from any other species of pigeon, or even from the other well-established races of the domestic pigeon, for the newly-formed fantail would be almost sure to inherit from its new progenitor some slight characteristic differences.” That the reasons here given satisfactorily explain why, in the vast majority of instances, lost species should not reap- pear, most naturalists will admit; but that they do not in them- selves sufficiently explain why such reappearance may not occasion- ally occur, may be reasonably contended. Thus, in the case of the birds referred to, it would by no means be unreasonable to suppose, even if such instances are a decided rarity, that the parent rock- pigeon, through some special adaptation to surrounding conditions, might have long survived the generations of fantails that were primarily derived from it, and that, at some future period, after a process of selection, a second series of fantails might have been produced practically identical with the first. The irregular dura- tion in length of time of species is well known to geologists, and its importance as a factor in evolution has been insisted upon by Mr. Darwin. It is probably true, as Darwin affirms, that ‘the parent-form will generally be supplanted and exterminated by its improved offspring ;” but it does not necessarily follow that the offspring will invariably prove to be of an improved stock, and, where this is not the case, there would be nothing very surprising in the survival of the parental form. The tenacity with which cer- tain specific characters adhere to some of the older genera, espe- cially of mollusks, is so great that paleontologists are frequently at a loss to determine just what characters separate practically the newest from the oldest species of a given genus. This is the case with the Nautili, and with a number of the brachiopods. Now, either we have here a retention through almost indefinite periods of primary specific characters, or a reversion (or a series of reversions) 186 GEOLOGICAL DISTRIBUTION. to a type once formed, but which has at one or more periods been effaced. If the former, would it be illogical to suppose that some of the numerous varieties or species that may have been evolved during a long lapse of ages from the parental stock should have proved less hardy than it, and should have, therefore, suffered much earlier extinction or modification? And, if so, what is there that we know that should absolutely prevent the same early extermi- nated forms from being re-evolved? It will be naturally assumed that the new and the old species, which appear to be so closely connected, are in reality distinct, and this may be true in all cases; but, if the distinguishing characters separating the two are almost imperceivable, it will require not much stretching of scientific prin- ciples to conceive that at least some of the resulting varieties may be strictly indistinguishable. Again, reverting to the case of the pigeons, it seems by no means clear, although such results may be of very rare occurrence, why a fantail, identical in every respect with the common form, may not be produced from a species of pigeon other than the rock- pigeon. It is true, as Darwin states, that newly-formed varieties would be almost sure to inherit from their progenitors certain dis- tinguishing traits or characters; but, as the formation of a species will depend upon the overbalancing by newly-acquired characters of those that may have been left by inheritance, there seems to be no reason why, through a process of selection and adaptation, such a convergence might not occasionally take place as would unite the ends of very distinct lines of descent. Paleontologists have long held to the opinion that the line of descent which leads up to the horse (genus Equus) in America is different from the similar line of Europe, and if it has been contended that the existing spe- cies, Equus caballus, was not in itself a product of the American line, but a modern European importation, its recent discovery in the Post-Pliocene deposits of this country proves the erroneousness of such an assumption. If, therefore, we are permitted to assume that two distinct lines of descent, the one passing through Eohip- pus, Orohippus, Mesohippus, Miohippus, Protohippus, and Plio- hippus, and the other through Palzotherium, Anchitherium, and Hipparion, lead up to an equivalent genus, the genus horse or Equus, would it be unreasonable to suppose that, with a continu- ance of the process of evolution, even the same species may be PARALLEL DEVELOPMENT OF SPECIES. 187 evolved ?* And, if this is possible, seeing that under apparently identical physical conditions the resulting genus became extinct on the American side of the Atlantic, while it still flourished on the European, might it not have so happened that the genus should have actually become extinct on the one continent before it even came into existence on the other? Assuming this condi- tion, we should then have a true case of extinction and reappear- ance, Similarly, in the case of the genus Tapirus, the tapir, it is by no means certain that the eastern and western forms are not the products of two distinct ancestral lines, independent in their evolution of such influences as might have been brought about by migration and interassociation.*™ It may, however, still be urged that the apparent development of parallel lines on the two continents is not in reality such, and that their independent convergence is merely the result of an inter- mixture of Old and New World types, during a period of land connection. That a union between the northern parts of the two hemispheres may have existed during the Eocene, and again in the Miocene and Pliocene periods, can very well be true, but that such a union need not necessarily imply the absolute inter-derivation of the two continental faunas can equally well be true. The complete absence from one continent of some of the more abundant fossil types occurring in the other, as the genera Paleotherium, Anoplo- therium, and Lophiodon from America, and Oreodon from Europe, proves that there must have been (granting land connection) some formidable check to migration ; and this assumption is further borne out by the circumstance of the irregular appearance in time, on the two continents, of such animals as might readily be supposed to have been able to grapple with a northern barrier. * Orohippus has been identified by many paleontologists with Hyraco- therium, and Miohippus with Anchitherium.—Waagen, from his studies of the Indian Jurassic Ammonitide, has arrived at the conclusion that the genus Aspidoceras (Ammonites auct. pars) has descended from at least two distinct generic roots, and further maintains that the same duplex or multiple origin can be traced in other genera as well (‘‘ Paleontologia Indica,”’ ser. ix., 4, 1875, p. 241). He also affirms that certain species of Phylloceras, as, for example, P. ptychoicum and P. Benacense, common to both Europe and In- dia, are the product, in the two countries, of distinct ancestral lines, con- vergent modification, as ‘‘dependent on laws which were innate’’ in the spe- cies, having brought about an identical result (doc. cét., p. 243). 188 GEOLOGICAL DISTRIBUTION. Among the Invertebrata we have also, as has already been inti- mated, well-marked instances of apparent reappearance. Mr. Da- vidson, in his review of the British fossil Brachiopoda,®* affirms that the resemblance between the recent Rhynchonella nigricans; which has nowhere as yet been found in any Tertiary deposit, ‘“and some Cretaceous and Jurassic forms is so great that we are at a loss to define their differences.” And, further, that certain varieties of the Mediterranean Terebratulina caput-serpentis, whose range extends downwards only to the Pliocene, so closely re- semble the Cretaceous Terebratula striata as to render the two barely, if at all, distinguishable. It may be that at some future date intermediate links will be discovered to unite the forms of the two periods; but who can, in the meantime, affirm that these are not true cases of reappearance? If it is true, as M. Barrande asserts, that the Triassic Nautilide show less affinity to existing species than do the primitive forms—in other words, that the recent species are more closely related to the original forms than the forms of a half-way intermediate period—are we not justified in assuming that there is here a reversion, or tendency towards a reversion, to specific characters once lost ? Among the Foraminifera we have several notable instances of apparent specific longevity, as, for example, the recurrence in the modern seas of some of the cre- taceous species of Globigerina, Cristellaria, and Glandaria; and, not unlikely, seeing how very slow must of necessity be the variation in this class of animals, by reason of their ready adaptability to their surroundings, the same forms will, on future investigation, be found to date considerably further back in the geological scale. It must not be construed, from the preceding argument, that we have attempted to prove the frequency of specific reappearances. These, if they actually have existed, which is not unlikely, were, doubtless, of exceptional occurrence, and in no way affect the prob- lem of progressive development. It might be objected that, if the views here set forth are correct in their application to species, they must also apply in a corresponding degree to some of the higher animal groups—genera, for example. This is certainly true, and, indeed, it may well be asked, What insuperable obstacle is there, that we know of, that should absolutely prevent the occasional re- appearance of a lost genus? Assuming, with many paleontologists, that Goniatites is a genus evolved from Nautilus, either directly or REAPPEARANCE OF GENERA. 189 indirectly, what is there, in view of the persistence of the nautiloid type, to preclude the possibility of the same genus being re-evolved ? There may be a sufficiency of reasons with which we are not ac- quainted ; but if, with our present limited knowledge, we are unable to indicate what these may be, it is scarcely fair to insist, a priori, upon their existence. It is true, we have no special reasons for as- suming why the Nautilus should become modified into a Goniatites; but this of itself is no proof that it may not. Numerous instances of genera widely separated by formations in which no representative of their tribe is to be met with are known to every paleontologist, but perhaps no more remarkable example is presented than that of the genus Nummulites. It has been well said by Mr. Brady” that ‘‘there are few time-mnarks in the geological record that have been regarded as better established, or more definite, than the first appearance of the Nummulite, at or near the commencement of the Tertiary epoch,” and so little, in fact, is known of any of the ante- cedent forms, that many, if not most, paleontologists of the present day still hold to the correctness of the view here stated. The re- searches of Gimbel and Brady have, however, placed beyond all doubt the existence of at least one Jurassic species (Nummulites Ju- rassica, Franconia) and one Carboniferous (N. pristina, Belgium), and not unlikely a somewhat doubtful form, N. variolaria, var. prima, described from the Cretaceous rocks of Palestine, will, on further investigation, prove to be a true member of the genus to which it has been referred. That we have here an instance of generic reappearance it is impossible to affirm, but it is certainly almost inconceivable, whichever way it be considered, that a group of animals, so extensively developed as are the Nummulites in the Tertiary deposits, should have left practically no traces of their existence behind them in the deposits next preceding the Tertiary, the Cretaceous, when their ancestry dates so far back as the Car- boniferous epoch. It is scarcely possible that at no period of time between the Carboniferous and Tertiary epochs should the condi- tions for their development have been favourable; and equally im- probable does it appear that, if such development actually did take place, we should so thoroughly lose sight of their remains. Grant- ing the absolutely unfavourable conditions, however, can it be readily imagined that a few miserable forms, evolved at an entirely unpropitious moment, should have battled through the struggle for 190 GEOLOGICAL DISTRIBUTION. existence to develop after an interval of millions of years? This seems very improbable, but yet it may be so; but why may it not also have been that, in the Carboniferous form, we had prema- ture evolution, with subsequent extinction, and that at a much more recent period « re-evolution of the same form, under more favourable circumstances, took place? The case is certainly very extraordinary, and probably has no parallel in the history of pale- ontology. On Appearance and Extinction.—It would naturally be sup- posed on the hypothesis of evolution that the introduction of all species must be a very gradual one, for it can scarcely be conceived that the laws governing the formation of new species through de- scent and modification could be anything but very slow in their action. So true is this, that Darwin has himself admitted, that ‘if numerous species, belonging to the same genera or families, have really started into life at once, the fact would be fatal to the theory of descent, with slow modification through natural se- lection ” (‘‘ Origin of Species”). Yet if we glance over the geo- logical record we cannot fail to note a very considerable num- ber of seemingly flagrant contradictions, groups of allied species appearing in almost every formation with apparently the greatest possible abruptness. We have but to instance as examples the genera of articulate brachiopods, and the tabulate corals of the Silurian period, the ganoid fishes of the Devonian period, the Tertiary placental mammals, and the foraminiferal genus Num- mulites, already referred to. Probably there exists no more strik- ing illustration of the abrupt or sudden development of a family than is furnished by the Nautilide, a group of animals for whose elucidation we are principally indebted to the labours of M. Bar- rande. Of this family of cephalopods, which comprises probably upwards of two thousand distinct species, no less than four hun- dred and sixty-three species, referable to some fifteen or more genera, are already represented in the Lower Silurian formation, although from the preceding Cambrian deposits at best only two well-authenticated forms (Cyrtoceras preecox and Orthoceras seri- ‘ceum) are known. Of this number about two hundred and sixty belong to the genus Orthoceras itself, ninety to Cyrtoceras, and forty-six to Endoceras, the last, a genus restricted absolutely to the Lower Silurian deposits. Facts such as these have been eager- APPEARANCE AND EXTINCTION. 191 ly seized hold of by the advocates of the doctrine of independ- ent and successive creations as proving the fallacy of any slow modification theory of transformism, and were it not that they are in themselves fallacious, would alone be sufficient to overthrow any such theory. For not alone must of necessity the development of a group of forms, all of which were descended from some one pro- genitor, have been an extremely slow process, but the ‘‘ progenitors must have lived long ages before their modified descendants.” The experience of every paleontologist proves to him, however, how misleading are those apparent abrupt appearances, and how very frequently groups of forms, supposed to be restricted to a definite horizon or formation, suddenly appear in a region perhaps not hitherto worked over, of, even where the work of the geologist has been accomplished with a sufficient amount of care, in a horizon of considerably older date. Almost every large group of animals furnishes such instances of antedating. No fact was at one time considered to be more firmly established than that the Mammalia belonged exclusively to the Tertiary and Post-Tertiary epochs, and yet we now know of their existence, even in considerable variety, in the deposits of both Jurassic and Triassic age; the serpents, which until quite recently were thought to have their earliest ancestors in the deposits of the Tertiary age, have been traced back to the Cretaceous (France); the Insecta, whose supposed earliest appearance in the Carboniferous rocks was considered to mark an epoch in the faunal development of that period, have, in a series of impressions left in the Devonian shale of New Bruns- wick, proved their existence at a much earlier date, and only with- in the past year, 186485, the announcement is made of the dis- covery of scorpion remains in the Silurian rocks of both Sweden and Scotland. It will still be in the memory of many geolo- gists and paleontologists with what startling effect the announce- ment of the discovery of the first air-breathing vertebrates in the deposits of the coal was made, at the very time when the absence of such forms was ascribed to the impossibility of their breathing an atmosphere supercharged with carbonic acid! In the case of special genera we have equally well-marked instances of anteda- ting. Waagen’s discovery of an ammonite in the Carboniferous rocks of the Salt-Range of India was for a long time discredited, so firmly 192 GEOLOGICAL DISTRIBUTION. had the notion that the ammonites were restricted to the Mesozoic era been engrafted on the minds of paleontologists; but now, sev- eral individuals, belonging to two or more species, have been ob- tained from the same deposits, and one closely related form has been quite recently described from the nearly equivalent deposits of Texas.*® M. Barrande has laid great stress upon the sudden ap- pearance, side by side, and in the full plenitude of their characters, of the more distinctive genera of cephalopods (Orthoceras, Cyrto- ceras, Nautilus, Trochoceras, Bathmoceras) in the first aspect of his second Silurian fauna (Lower Silurian of geologists generally), and their complete absence from the Primordial Zone (Cambrian) ; but we have seen that at least two of the genera, Orthoceras and Cyrtoceras, have since been traced back to the earlier formation. Almost every chapter in geological history indicates some such case of antedating, and proves to the paleontologist how very cautious he should be in his limitation to.time of particular groups of or- ganisms. It cannot be expected that in any portion of the earth’s surface will there ever be found a complete sequence of the geologi- cal formations, nor can we hope satisfactorily to bridge over in all cases the gaps that occur in one locality with the deposits found in another. The unequal period of time during which land areas have been laid dry or been kept submerged beneath water, in con- junction with the devastating effects of denudation, render such a complete restoration of the series impossible, and as long as this is so, the work of the paleontologist must inevitably be riddled with ‘‘breaks” in the geological record. It is surprising, in view of these facts, which are too obvious to be overlooked, with what tenacity some paleontologists insist upon absolute limitation of species, or groups of species, and how slow they are to accept any new facts bearing upon distribution in time that might in any way disturb the harmony of their preconceived notions. There is ‘perhaps no more patent fact in the history of the physical de- velopment of our planet than the imperfection of the geological record, the full realisation of which could not fail to dispel many of the singular notions that still prevail relative to the support which paleontology brings to the doctrine of evolution. It has been objected that, in assuming the universality of breaks, we are drawing largely upon our fancy, and that conditions which do not exist in fact are arranged to suit the views of the evolution- PALEONTOLOGICAL BREAKS. 193 ist. This may be true in a limited number of cases; but there is every reason to believe that the constancy of breaks is even far greater than the most enthusiastic advocate of the doctrine of im- perfection would be ready to admit. For, even in such areas where the rock-masses through a general uniformity of character would seem to indicate continuous sedimentation, have we always definite proof that the sedimentation was really continuous? Far from it. If, for example, certain parts of the Atlantic border of the United . States were depressed beneath the sea, and a new Post-Tertiary deposit imposed upon them, we might be not a particle the wiser, as far as stratigraphical and lithological evidence went to show, for the enormous period of time that intervened between the formation of the newest and next newest (Miocene) series of deposits. The strata would lie practically conformably on one another, and it would require but little degradation to plane down these inequalities, which would otherwise indicate an eroded land surface. The mem- bers of the Cretaceo-Eocene series of the State of New Jersey, and elsewhere along the same coast, are so intimately related to one an- other, by conformability of position and lithological structure, that it might readily have been assumed that we had here an instance of continuous sedimentation; and, indeed, for a long time no division- line was supposed to exist. But the unmistakable evidence of pale- ontology proves that here, as well as at most parts of the earth’s surface which have been made accessible to the geologist, a break marks the junction of the Cretaceous and Tertiary formations. It must be admitted that there are certain anomalies connected with the occurrence of breaks which have not thus far received an adequate explanation. Their broad distribution—it might, indeed, almost be said universality—in equivalent periods of time, has long been noted as a surprising fact, and one that still remains in the nature of a puzzle to the geologist. Nowhere on the surface of the earth has there as yet been found a distinct connection between the Paleozoic and Mesozoic series of deposits, and only at a very few points (India, New Zealand, California) what may be considered to be an unequivocal link between the Mesozoic and Cainozoic series (Cretaceous and Tertiary). It is true that the field surveyed by the geologist is of comparatively limited extent, when compared with that which still remains to be explored—the greater part of the conti- nents of Asia, Africa, South America, and Australia—and it is but 14 194 GEOLOGICAL DISTRIBUTION. reasonable to expect that, in some of the regions here indicated, the connections will be found that elsewhere are wanting. But, even granting the justice of this plea, the facts, such as they are, are of themselves sufficiently remarkable, as indicating how very far- reaching in their action must have been the forces that were directly concerned in the causation of breaks. It is a little difficult to con- ceive of secular elevations and depressions of the land-surface ex- tending simultaneously over nearly the entire circumference of the earth, even in the restricted area of the Temperate Zone; but such must undoubtedly have been the case to account for the phenomena that are presented to us. Otherwise complete passage-beds would be of much more frequent occurrence than we know them to be. This does not preclude the possibility of the existence of local areas showing a differential or contrary movement; such, however, do not seem to have in any way interfered with the grand scheme that was involved. But it is very unlikely that elevation or subsidence either was, or could be, universal at any given period; on the contrary, it appears far more rational to suppose that every very extensive cleva- tion was accompanied by a corresponding depression somewhere else, and vice versa, and thus some sort of balance maintained. If this is so, then we would naturally look in some distant quarter for the counterpart of the effects which either elevation or subsidence * may have produced in any one region of the globe. Secing how very general throughout the vast expanse of the Northern Hemi- sphere are certain breaks in the geological series, are we not justi- fied in looking to the region farther south for the evidences prov- ing uninterrupted sedimentation and continuous organic evolu- tion ? If we attach full weight to the imperfection of the geological record, it is not difficult to account for the apparent abrupt ap- pearance of certain animal groups or faunas; indeed, the problem would have been far more difficult to solve had the case been other- wise. But there is one special instance of such appearance which is not so readily accounted for, and which, under any hypothesis, is almost inexplicable. We refer to the sudden appearance of the numerous forms of life which characterise the oldest fossiliferous formation with which we are at present acquainted, the Cambrian, * Reference is here made to the more extensive movements of the crust, producing the profounder breaks. PALEONTOLOGICAL BREAKS. 195 when no unequivocal traces of preexisting life are anywhere to be met with in the formation next preceding. So absolutely universal is this condition that it almost staggers belief. It cannot rationally be conceived that the varied Cambrian fauna could have come into existence de se, without there being a line of progenitors to account for its existence; but, if such progenitors did exist, which was doubtless the case, what has become of their remains? Can it be that all over the world, as far as we know, every fragment of such a pre-Cambrian fauna should have been so completely wiped out as to leave not a determinable vestige behind? It must be confessed this seems very incredible, seeing with what absolute perfection many of the oldest, and in many respects the most deli- cate, structures have been preserved through all the vicissitudes of geological time. The hexactinellid sponges of the Cambrian and Silurian periods, the Silurian Foraminifera, and scarcely less so the graptolités, bear ample testimony to a most astonishing power of re- sistance. To account for such a wholesale obliteration, we must in- voke the aid of a kind or degree of metamorphic action very different from that which has since been made known to us, for it can scarcely be supposed that the ordinary action extending back through only one more period of geological time could have produced such pro- found results. And it is not only from a comparatively brief period of time that we must explain the utter absence of organic traces, but from a period which, in the opinion of many geologists, may have been of equal duration with the entire interval that has elapsed since the deposition of the Cambrian sediments. But, even granting this unknowable form of regional metamorphism, it still remains a mys- tery how its effects could have been so universal as to wipe out every vestige of an indisputable pre-Cambrian fauna. It is very possible that the limestone of the Laurentian rocks owes its ex- istence to organic agencies, and therefore represents in part this earlier fauna; but even admitting this to be so, it helps the mat- ter very little, since the limestone is overlaid by younger crystal- line rocks, which are no less destitute of organic traces than the deposits underlying it. For the same reason the existence or non- existence, as an animal, of the much- debated Eozoon, does not affect the point at issue; on the contrary, the total absence of de- terminabie organic traces, either above or below the Eozoon line, would, in itself, apart from all other evidence, constitute strong 196 GEOLOGICAL DISTRIBUTION. grounds for relegating that guasi-organism to the class of mineral deposits. * Darwin has sought to explain the anomaly on the supposition that possibly the most ancient fossiliferous deposits lie buried deep beneath the floor of our existing oceans, and that they may have lain there ever since the Cambrian (Silurian) period. They would then have been kept out of sight, and would, at the same time, have offered no opportunities for their remains to become inter- mingled with those of any subsequent formations. That there is no insuperable objection to this explanation every one must admit, and that it, at least, partially meets the case, is more than prob- able. But it is still far from being in the nature of a demonstra- tion. The doctrine of the permanency of land areas and oceanic basins has much in its favour, and if true, would go far towards supporting Darwin’s proposition; but, unfortunately, the absolute proofs of such a condition are still wanting, and may forever re- main wanting. The land surfaces from which the Paleozoic rocks derived their sediments, either in part or in whole, may or may not have occupied the position of the present seas. If the former be the case, the problem remains in its original form; if the latter, it must be assumed that a broad hiatus exists between the Laurentian and Cambrian series, and that the gap is filled by vast submarine de- posits, upon which massive accumulations of continental and organic débris have been superimposed. Fossils of a pre-Cambrian type may be abundant in these deposits. Manifestly, however, the assump- tion of large land areas depressed beneath the sea carries with it the implication of an alternation of oceanic and continental surfaces, * The question of the animal nature of Eozoon has been practically settled in the negative through the researches of King, Rowney, Julien, and Mébius; the elaborate memoir on this subject by the last-mentioned scientist will proba- bly be considered conclusive by most impartial zoologists. The present author has himself examined masses of Eozoon rock in which the network of green mineral, supposed to fill the chamber-cavities of the giant foraminifer, coalesce and merge into a broad band of serpentine. Now, either we have here a true Eozoon structure or not. If yes, then on what zoological basis, it may be asked, can the gradual convergence of the infiltrating mineral and its final coalescence with a broad band of serpentine be explained? If the contrary, what necessity is there for invoking the aid of organic forces in the explanation of a structure, when one fully as intricate, and piactically undistinguishable from it, can be shown to be of purely mineral formation ? EXTINCTION OF SPECIES. 197 and if this could have happened once, why may it not have occurred again? Or might it be assumed that this, a primary oscillation, first marked out the existing boundaries of land and sea? The problem, in whichever light it may be viewed, is beset with in- numerable difficulties, and, it must be confessed, lies beyond the probability of a near solution. The evidence appears strong, how- ever, for concluding that the Archean rocks, so recognised—i. ¢., those of the Laurentian and Huronian series—are by no means the immediate predecessors of the Cambrian series. These may still be found at some places underlying the last, or they may forever remain hidden from view beneath the aqueous deep. Extinction.—It has very generally been remarked that the ex- tinction of species, or groups of species, appears to have been a much more gradual process than their introduction. This is, doubt- less, in great part true, and agrees well with the theory of natural selection. The formation of a new species usually implies favour- able conditions for the development of that species, and it is, therefore, not surprising that when once formed the species should spread very rapidly. When, however, through certain causes— the alteration of the physical properties of the surroundings or inferiority in the general struggle for existence —the conditions for existence are no longer as favourable as they were before, we should naturally expect to meet with a decline in the development of that species, and its possible ultimate extinction. But unless the change in the conditions of life were very abrupt, we should nowhere look for immediate or sudden extermination. Every one is familiar with what prodigious rapidity certain weeds, as the wild carrot, for example, have spread in regions into which they had but recently been introduced, but how very much slower has been the extermination of the species of native plants which they may have supplanted. The English sparrow has developed with sur- prising rapidity in the Eastern United States, and, although since the period of its introduction scarcely twenty years have elapsed, it has so far multiplied and become master of the newly acquired situation as to have practically appropriated for itself a large por- tion of the domain formerly occupied by the native birds of the same family, and to the exclusion of those birds. These, if they eventually prove weaker in the race, may in course of time com- pletely disappear, but, before that period will be reached, will 198 GEOLOGICAL DISTRIBUTION. doubtless have effected a foothold in some neighbouring region, and struggle on as best they can under what might be less favour- able conditions for existence. Ultimately the race will be thinned out and extinction of the species follow. A parallel case of sudden appearance and much less sudden disappearance is afforded by the two common species of house-rat, the black and the brown, both of which, through introduction, have become more or less cos- mopolitan in their range. Everywhere where the latter has suc- ceeded in obtaining a foothold the former is gradually, but steadily, fading away, relinquishing piece by piece the territory of which it was at one time in full possession, But it still lingers on, and, no doubt, will still continue to so linger for some time in the future, a relic of a once formidable race. Yet its own march of conquest was probably no less rapid than that of its more successful com- petitor, the brown or Norway rat, which appears to have been unknown west of the Volga River prior to about the middle of the last century, and which has since spread so extensively as to render it one of the commonest pests of both continental and insular Europe. The species was first observed on the Pacific coast of the United States subsequent to 1850, but it is scarcely less common at the present time in California than anywhere else. The relation of natural selection to extinction and persistence is clearly stated by Darwin thus (‘‘ Origin of Species”) : ‘‘The competition will generally be most severe, as formerly explained and illustrated by examples, between the forms which are most like to each other in all respects. Hence the improved and modified descendants of a species will generally cause the extermination of the parent species; and if many new forms have been developed from any one species, the nearest allies of that species, 7. ¢., the species of the same genus, will be the most liable to extermination. Thus, as I believe, a number of new species descended from one species, that is, a new genus, comes to supplant an old genus belonging to the same family. But it must often have happened that a new species be- longing to some one group will have seized on the place occupied by a species belonging to a distinct group, and thus cause its exter- mination; and, if many allied forms be developed from the success- ful intruder, many will have to yield their places, and it will gen- erally be allied forms, which will suffer from some inherited inferi- ority in common. But, whether it be species belonging to the same EXTINCTION OF ANIMAL GROUPS. 199 or to a distinct class which yield their places to other species which have been improved and modified, a few of the sufferers may often long be preserved, from being fitted to some peculiar line of life, or from inhabiting some distant or isolated station, where they have escaped severe competition. For instance, some species of Trigonia, a great genus of shells in the secondary formations, survive in the Australian seas; and a few members of the great and almost extinct group of ganoid fishes still inhabit our fresh waters. Therefore the utter extinction of a group is generally, as we have seen, a slower process than its production.” There are instances, however, in which the extinction of certain animal groups is generally considered to have been very sudden. The trilobites and ammonites among invertebrates, and the dino- saurian reptiles among vertebrates, may be taken in illustration of such cases. But even here a careful examination of the premises shows that the suddenness of extinction is probably much more apparent than real, and that, as the facts now stand, they by no means sustain the inferences that have been drawn from them. The trilobites, for example, are frequently stated to stop suddenly at the close of the Paleozoic era, whereas, as a matter of fact, no trace of trilobites has ever been found in deposits unequivocally newer than the Carboniferous. A whole period (Permian)—true, a comparatively insignificant one—therefore, still intervenes be- tween the extinction of the order and the close of the Paleozoic era. But, again, even with the Carboniferous period the extinc- tion is far from being sudden. Of the numerous genera which so eminently characterise the Silurian fauna, only two genera, Phillipsia and Proetus, both of thent restricted to a comparative- ly insignificant number of species, survive the Devonian period.* These, together with two other genera now for the first time in- troduced, Griffithides and Brachymetopus, constitute the entire known Carboniferous trilobitic fauna; and of this limited number only one genus, Phillipsia, and that apparently in America alone, passes up as high in the Carboniferous series as the Coal-Measures. We thus see how very gradual, rather than abrupt, has been the final —if final—extermination of this order of animals. Nor do we have that sudden downfall, either in or from the * Since the above was written, Professor Claypole has announced the dis- covery of Dalmania in the Waverly Group (Lower Carboniferous) of Ohio. 200 GEOLOGICAL DISTRIBUTION. ~ Silurian period, which many authors are in the habit of insisting upon. Thus, if we take the very elaborate tables of Mr. Etheridge”? as our guide, we find that the rise and fall of the British trilobitic fauna has been, on the whole, gradual, the greatest break occurring between the Llandeilo and Caradoc on the one side, and the Cara- doc and Llandovery on the other, or along the horizon which, by many geologists, is considered to mark a ‘‘ Middle” Silurian divi- sion. The following scheme will exhibit the numerical, generic, and specific values presented by the different horizons of the Paleozoic series, from the base of the Silurian to the Carboniferous, inclusive: FORMATIONS. Genera of Trilobites. Species. ATODIG 522