The two next orders consist of but a single family each, viz.:
We now come to the Rodentia, a very extensive and difficult order, in which there is still much difference of opinion as to the details of classification, although the main outlines are pretty well settled. The foundations of a true classification of this order were laid by Mr. G. R. Waterhouse more than thirty years ago, and succeeding authors have done little more than follow his arrangement with unimportant modifications. Professor Lilljeborg, of Upsala, has however made a special study of this group of animals, and has given an original and detailed classification of all the genera. (Systematisk Öfversigt af de Gnagande Däggdjuren, Glires. Upsala, 1866.) I follow this arrangement with a few slight modifications suggested by other naturalists, and which make it better adapted for the purposes of this work.
Order—RODENTIA.
The Edentata have been classified by Mr. Turner, in theProceedings of the Zoological Society(1851, p. 205), by Dr. Gray in the British Museum Catalogue, and by Professor Carus in hisHandbuch. The former takes a middle course betweenthe numerous families of Dr. Gray, seven in number, and the two families to which Professor Carus restricts the existing species. I therefore follow Mr. Turner.
Order—EDENTATA.
The Marsupials have been well classified and described by Mr. Waterhouse in the first volume of hisNatural History of Mammalia, and his arrangement is here followed. The suborders adopted by Professor Carus are also given.
Order—MARSUPIALIA.
Order—MONOTREMATA.
The last order, the Monotremata, consist of two families, which Professor Carus combines into one, but which it seems more natural to keep separate.
BIRDS.
Birds are perhaps the most difficult to classify of all the divisions of the vertebrata. The species and genera are exceedingly numerous, and there is such a great uniformity in general structure and even in the details of external form, that it is exceedingly difficult to find characters by which orders and families can be characterised. For a long time the system of Vigors and Swainson was followed; but this wholly ignored anatomical characters and in many cases plainly violated well-marked affinities. Characters derived from the form of the sternum, the scutellation of the tarsi, and the arrangement of the feathers, have all assisted in determining natural groups. More recently Professor Huxley has applied the variations of the bony palate to the general arrangement of birds; and still more recently Professor Garrod has studied certain leg-muscles for the same purpose. The condition of the young as regards plumage, and even the form, texture, and coloration of the egg, have also been applied to solve doubtful cases of affinity; yet the problem is not settled, and it will probably remain for another generation of ornithologists to determine with any approach to accuracy what are the most natural divisions of the class into orders and families. In a work like the present it is evidently not advisable to adopt all the recent classifications; since experience has shown that no arrangement in which one set of characters is mainly relied on, long holds its ground. Such modifications of the old system as seem to be well established will be adopted; but the older groups will be adhered to in cases where the most recent classifications are open to doubt, or seem inconvenient as separating families, which, owing to their similarity in general structure, form and habits are best kept together for the purposes of geographical distribution.
The old plan of putting the birds of prey at the head of the class, is now almost wholly given up; both because they are notthe most highly organised, but only one of the most specialised forms of birds, and because their affinities are not with the Passeres, but rather with the cormorants and some other of the aquatic groups. The Passeres therefore are placed first; and the series of families is begun by the thrushes, which are certainly the most typical and generally well-organised form of birds. Instead of the Scansores and Fissirostres of the older authors, the order Picariæ, which includes them both, is adopted, but with some reluctance; as the former are, generally speaking, well marked and strongly contrasted groups, although certain families have been shown to be intermediate. In the Picariæ are included the goat-suckers, swifts, and humming-birds, sometimes separated as a distinct order, Macrochires. The parrots and the pigeons form each a separate order. The old groups of Grallæ and Anseres are preserved, as more convenient than breaking them up into widely separated parts; for though the latter plan may in some cases more strictly represent their affinities, its details are not yet established, nor is it much used by ornithologists. In accordance with these views the following is the series of orders and families of birds adopted in this work:
Class—AVES.
The Passeres consist of fifty families, which may be arranged and grouped in series as follows. It must however be remembered that the first family in each series is not always that which is most allied to the last family of the preceding series. All extensive natural groups consist of divergent or branching alliances, which renders it impossible to arrange the whole in one continuous series.
46. Pteroptochidæ
The preceding arrangement is a modification of that proposed by myself in theIbis(1874, p. 406). The principal alterations are adding the families Panuridæ and Sittidæ in series A, commencing series B with Dicæidæ; bringing Vireonidæ next to the allied American family Mniotiltidæ; and placing Motacillidæ in series C next to Alaudidæ. At the suggestion of Professor Newton I place Menuridæ and Atrichidæ apart from the other Passeres, as they both possess striking peculiarities of anatomical structure.
The heterogeneous families constituting the order Picariæ may be conveniently arranged as follows:
The Psittaci or parrot tribe are still in a very unsettled state of classification; that recently proposed by Professor Garrod differing widely from the arrangement adopted in Dr. Finsch's monograph of the order. Taking advantage of the researches of these and other authors, the following families are adopted as the most convenient in the present state of our knowledge:
The Columbæ, or pigeons, are also in a very unsatisfactory state as regards a natural classification. The families, sub-families, and genera proposed by various authors are very numerous, and often quite irreconcilable. I therefore adopt only two families; and generally follow Mr. G. R. Gray's hand-list for the genera, except where trustworthy authorities exist for a different arrangement. The families are:
The Gallinæ, or game-birds, may be divided into seven families:
The Opisthocomi consist of one family containing a single species, the "Hoatzin" of Guiana.
Family 93. Opisthocomidæ.
The Accipitres, or birds of prey, which were long considered to be the highest and most perfect order of birds, are now properly placed lower down in the series, their affinities being more with the aquatic than with the perching birds. The following is the arrangement adopted by Mr. Sharpe in his recently published British Museum catalogue of diurnal birds of prey:—
The Grallæ or Grallatores are in a very unsettled state. The following series of families is in accordance with the views of some of the best modern ornithologists:
The Anseres or Natatores are almost equally unsettled. The flamingoes are usually placed in this order, but their habits best assort with those of the waders.
The last order of birds is the Struthiones or Ratitæ, considered by many naturalists to form a distinct sub-class. It consists of comparatively few species, either living or recently extinct.
REPTILES.
In reptiles I follow the classification of Dr. Günther as given in thePhilosophical Transactions, vol. clvii., p. 625. He divides the class into five orders as follows:—
In the arrangement of the families comprised in each of these orders I also follow the arrangement of Dr. Günther and Dr. J. E. Gray, as given in the British Museum Catalogue, or as modified by the former gentleman who has kindly given me much personal information.
The Ophidia, or Snakes, form the first order and are classified as follows:—
The second order, Lacertilia, are arranged as follows:—
44. Lialidæ.
The third order, Rhyncocephalina consists of a single family:—
53. RhyncocephalidæThe Hatteria of New Zealand.
The fourth order, Crocodilia or Loricata, consists of three families:—
The fifth order, Chelonia, consists of four families:—
AMPHIBIA.
In the Amphibia I follow the classification of Professor Mivart, as given for a large part of the order in theProceedings of the Zoological Societyfor 1869. For the remainder I follow Dr. Strauch, Dr. Günther, and a MSS. arrangement kindly furnished me by Professor Mivart.
The class is first divided into three groups or orders, and then into families as follows:—
Order I.—PSEUDOPHIDIA.
Order II.—BATRACHIA URODELA.
Order III.—BATRACHIA ANOURA.
FISHES.
These are arranged according to the classification of Dr. Günther, whose great work "The British Museum Catalogue of Fishes," has furnished almost all the material for our account of the distribution of the class.
In that work all existing fishes are arranged in six sub-classes and thirteen orders. A study of the extraordinaryCeratodusfrom Australia has induced Dr. Günther to unite three of his sub-classes; but as his catalogue will long remain a handbook for every student of fishes, it seems better to follow the arrangement there given, indicating his later views by bracketing together the groups he now thinks should be united.
INSECTS.
The families and genera of insects are so immensely numerous, probably exceeding fifty-fold those of all other land animals, that for this cause alone it would be impossible to enter fully into their distribution. It is also quite unnecessary, because many of the groups are so liable to be transported by accidental causes, that they afford no useful information for our subject; while others are so obscure and uninteresting that they have been very partially collected and studied, and are for this reason equally ineligible. I have therefore selected a few of the largest and most conspicuous families, which have been so assiduously collected in every part of the globe, and so carefully studied at home, as to afford valuable materials for comparison with the vertebrate groups, when we have made due allowance for the dependence of many insects on peculiar forms of vegetation, and the facility with which many of them are transported either in the egg, larva, or perfect state, by winds, currents, and other less known means.
I confine myself then, almost exclusively, to the sixteen families of Diurnal Lepidoptera or butterflies, and to six of the most extensive, conspicuous, and popular families of Coleoptera.The number of species of Butterflies is about the same as that of Birds, while the six families of Coleoptera selected, comprise more than twenty thousand species, far exceeding the number of all other vertebrates. These families have all been recently catalogued, so that we have very complete information as to their arrangement and distribution.
LEPIDOPTERA DIURNA, OR BUTTERFLIES.
COLEOPTERA, OR BEETLES.
The above families comprise the extensive series of ground beetles (Carabidæ) containing about 9,000 species, and the Longicorns, which are nearly as numerous and surpass them in variety of form and colour as well as in beauty. The Cetoniidæ and Buprestidæ are among the largest and most brilliant of beetles; the Lucanidæ are pre-eminent for remarkable form, and the Cicindelidæ for elegance; and all the families are especial favourites with entomologists, so that the whole earth has been ransacked to procure fresh species.
Results deduced from a study of these will, therefore, fairly represent the phenomena of distribution of Coleoptera, and, as they are very varied in their habits, perhaps of insects in general.
MOLLUSCA.
The Mollusca are usually divided into five classes as follows:—
The Gasteropoda and Conchifera alone contain land and freshwater forms, and to these we shall chiefly confine our illustrations of the geographical distribution of the Mollusca. The classification followed is that of Dr. Pfeiffer for the Operculata and Dr. Von Martens for the Helicidæ. The families chiefly referred to are:—
Class II.—GASTEROPODA.
Order 2.—Pulmonifera.
PART II.
ON THE DISTRIBUTION OF EXTINCT ANIMALS.
THE EXTINCT MAMMALIA OF THE OLD WORLD.
Although it may seem somewhat out of place to begin the systematic treatment of our subject with extinct rather than with living animals, it is necessary to do so in order that we may see the meaning and trace the causes of the existing distribution of animal forms. It is true, that the animals found fossil in a country are very generally allied to those which still inhabit it; but this is by no means universally the case. If it were, the attempt to elucidate our subject by Palæontology would be hopeless, since the past would show us the same puzzling diversities of faunas and floras that now exist. We find however very numerous exceptions to this rule, and it is these exceptions which tell us of the past migrations of whole groups of animals. We are thus enabled to determine what portion of the existing races of animals in a country are descendants of its ancient fauna, and which are comparatively modern immigrants; and combining these movements of the forms of life with known or probable changes in the distribution of land and sea, we shall sometimes be able to trace approximately the long series of changes which have resulted in the actual state of things. To gain this knowledge is our object in studying the "Geographical Distribution of Animals," and our plan of study must be determined, mainly, by the facilities it affords us for attaining this object. In discussing the countless details of distribution we shall meet with in our survey of the zoological regions, we shall often find it useful to refer to the evidence we possess of the range of the group in question inpast times; and when we attempt to generalise the phenomena on a large scale, with the details fresh in our memory, we shall find a reference to the extinct faunas of various epochs to be absolutely necessary.
The degree of our knowledge of the Palæontology of various parts of the world is so unequal, that it will not be advisable to treat the subject under each of our six regions. Yet some subdivision must be made, and it seems best to consider separately the extinct animals of the Old and of the New Worlds. Those of Europe and Asia are intimately connected, and throw light on the past changes which have led to the establishment of the three great continental Old World regions, with their various subdivisions. The wonderful extinct fauna recently discovered in North America, with what was previously known from South temperate America, not only elucidates the past history of the whole continent, but also gives indications of the mutual relations of the eastern and western hemispheres.
The materials to be dealt with are enormous; and it will be necessary to confine ourselves to a general summary, with fuller details on those points which directly bear upon our special subject. The objects of most interest to the pure zoologist and to the geologist—those strange forms which are farthest removed from any now living—are of least interest to us, since we aim at tracing the local origin or birthplace of existing genera and families; and for this purpose animals whose affinities with living forms are altogether doubtful, are of no value whatever.
The great mass of the vertebrate fossils of the tertiary period consist of mammalia, and this is precisely the class which is of most value in the determination of zoological regions. The animals of the secondary period, though of the highest interest to the zoologist are of little importance to us; both because of their very uncertain affinities for any existing groups, and also because we can form no adequate notion of the distribution of land and sea in those remote epochs. Our great object is to trace back, step by step, the varying distribution of the chief forms of life; and to deduce, wherever possible, the physical changes which must have accompanied or caused such changes.The natural division of our subject therefore is into geological periods. We first go back to the Post-Pliocene period, which includes that of the caves and gravels of Europe containing flint implements, and extends back to the deposit of the glacial drift in the concluding phase of the glacial epoch. Next we have the Pliocene period, divided into its later portion (the Newer Pliocene) which includes the Glacial epoch of the northern hemisphere; and its earlier portion (the Older Pliocene), represented by the red and coralline crag of England, and deposits of similar age in the continent. During this earlier epoch the climate was not very dissimilar from that which now prevails; but we next get evidence of a still earlier period, the Miocene, when a warmer climate prevailed in Europe, and the whole fauna and flora were very different. This is perhaps the most interesting portion of the tertiary deposits, and furnishes us with the most valuable materials for our present study. Further back still we have the Eocene period, with apparently an almost tropical climate in Europe; and here we find a clue to some of the most puzzling facts in the distribution of living animals. Our knowledge of this epoch is however very imperfect; and we wait for discoveries that will elucidate some of the mystery that still hangs over the origin and migrations of many important families. Beyond this there is a great chasm in the geological record as regards land animals; and we have to go so far back into the past, that when we again meet with mammalia, birds, and land-reptiles, they appear under such archaic forms that they cease to have any local or geographical significance, and we can only refer them to wide-spread classes and orders. For the purpose of elucidating geographical distribution, therefore, it is, in the present state of our knowledge, unnecessary to go back beyond the tertiary period of geology.
The remains of Mammalia being so much more numerous and important than those of other classes, we shall at first confine ourselves almost exclusively to these. What is known of the birds, reptiles, and fishes of the tertiary epoch will be best indicated by a brief connected sketch of their fossils in all parts of the globe, which we shall give in a subsequent chapter.