tarting with the idea； that 〃each species must have been created within and over the geographical area； which it now occupies；〃 he concluded 〃that the most natural primary ontological divisions of the Earth's surface〃 were those six regions； which since their adoption by Wallace in his epoch…making work； have become classical。 Broadly speaking； these six regions are equivalent to the great masses of land； they are convenient terms for geographical facts； especially since the Palaearctic region expresses the unity of Europe with the bulk of Asia。 Sclater further brigaded the regions of the Old World as Palaeogaea and the two Americas as Neogaea； a fundamental mistake； justifiable to a certain extent only since he based his regions mainly upon the present distribution of the Passerine birds。
Unfortunately these six regions are not of equal value。 The Indian countries and the Ethiopian region （Africa south of the Sahara） are obviously nothing but the tropical； southern continuations or appendages of one greater complex。 Further； the great eastern mass of land is so intimately connected with North America that this continent has much more in common with Europe and Asia than with South America。 Therefore； instead of dividing the world longitudinally as Sclater had done； Huxley； in 1868 （〃On the classification and distribution of the Alectoromorphae and Heteromorphae〃； 〃Proc。 Zool。 Soc。〃 1868； page 294。）； gave weighty reasons for dividing it transversely。 Accordingly he established two primary divisions； Arctogaea or the North world in a wider sense； comprising Sclater's Indian； African； Palaearctic and Neartic regions； and Notogaea； the Southern world； which he divided into （1） Austro…Columbia （an unfortunate substitute for the neotropical region）； （2） Australasia； and （3） New Zealand； the number of big regions thus being reduced to three but for the separation of New Zealand upon rather negative characters。 Sclater was the first to accept these four great regions and showed； in 1874 （〃The geographical distribution of Mammals〃； 〃Manchester Science Lectures〃； 1874。）； that they were well borne out by the present distribution of the Mammals。
Although applicable to various other groups of animals； for instance to the tailless Amphibia and to Birds （Huxley himself had been led to found his two fundamental divisions on the distribution of the Gallinaceous birds）； the combination of South America with Australia was gradually found to be too sweeping a measure。 The obvious and satisfactory solution was provided by W。T。 Blanford （Anniversary address （Geological Society； 1889）； 〃Proc。 Geol。 Soc。〃 1889…90； page 67； 〃Quart。 Journ。〃 XLVI 1890。）； who in 1890 recognised three main divisions； namely Australian； South American； and the rest； for which the already existing terms （although used partly in a new sense； as proposed by an anonymous writer in 〃Natural Science〃； III。 page 289） 〃Notogaea；〃 〃Neogaea〃 and 〃Arctogaea〃 have been gladly accepted by a number of English writers。
After this historical survey of the search for larger and largest or fundamental centres of animal creation； which resulted in the mapping of the world into zoological regions and realms of after all doubtful value； we have to return to the year 1858。 The eleventh and twelfth chapters of 〃The Origin of Species〃 （1859）； dealing with 〃Geographical Distribution；〃 are based upon a great amount of observation； experiment and reading。 As Darwin's main problem was the origin of species； nature's way of making species by gradual changes from others previously existing； he had to dispose of the view； held universally； of the independent creation of each species and at the same time to insist upon a single centre of creation for each species； and in order to emphasise his main point； the theory of descent； he had to disallow convergent； or as they were then called； analogous forms。 To appreciate the difficulty of his position we have to take the standpoint of fifty years ago； when the immutability of the species was an axiom and each was supposed to have been created within or over the geographical area which it now occupies。 If he once admitted that a species could arise from many individuals instead of from one pair； there was no way of shutting the door against the possibility that these individuals may have been so numerous that they occupied a very large district； even so large that it had become as discontinuous as the distribution of many a species actually is。 Such a concession would at once be taken as an admission of multiple； independent； origin instead of descent in Darwin's sense。
For the so…called multiple； independently repeated creation of species as an explanation of their very wide and often quite discontinuous distribution； he substituted colonisation from the nearest and readiest source together with subsequent modification and better adaptation to their new home。
He was the first seriously to call attention to the many accidental means； 〃which more properly should be called occasional means of distribution；〃 especially to oceanic islands。 His specific； even individual； centres of creation made migrations all the more necessary； but their extent was sadly baulked by the prevailing dogma of the permanency of the oceans。 Any number of small changes （〃many islands having existed as halting places； of which not a wreck now remains〃 （〃The Origin of Species〃 （1st edition）； page 396。）。） were conceded freely； but few； if any； great enough to permit migration of truly terrestrial creatures。 The only means of getting across the gaps was by the principle of the 〃flotsam and jetsam；〃 a theory which Darwin took over from Lyell and further elaborated so as to make it applicable to many kinds of plants and animals； but sadly deficient； often grotesque； in the case of most terrestrial creatures。
Another very fertile source was Darwin's strong insistence upon the great influence which the last glacial epoch must have had upon the distribution of animals and plants。 Why was the migration of northern creatures southwards of far…reaching and most significant importance？ More northerners have established themselves in southern lands than vice versa； because there is such a great mass of land in the north and greater continents imply greater intensity of selection。 〃The productions of real islands have everywhere largely yielded to continental forms。〃 （Ibid。 page 380。）。。。〃The Alpine forms have almost everywhere largely yielded to the more dominant forms generated in the larger areas and more efficient workshops of the North。〃
Let us now pass in rapid survey the influence of the publication of 〃The Origin of Species〃 upon the study of Geographical Distribution in its wider sense。
Hitherto the following thought ran through the minds of most writers： Wherever we examine two or more widely separated countries their respective faunas are very different； but where two faunas can come into contact with each other； they intermingle。 Consequently these faunas represent centres of creation； whence the component creatures have spread peripherally so far as existing boundaries allowed them to do so。 This is of course the fundamental idea of 〃regions。〃 There is not one of the numerous writers who considered the possibility that these intermediate belts might represent not a mixture of species but transitional forms； the result of changes undergone by the most peripheral migrants in adaptation to their new surroundings。 The usual standpoint was also that of Pucheran （〃Note sur l'equateur zoologique〃； 〃Rev。 et Mag。 de Zoologie〃； 1855； also several other papers； ibid。 1865； 1866； and 1867。） in 1855。 But what a change within the next ten years！ Pucheran explains the agreement in coloration between the desert and its fauna as 〃une harmonie post…etablie〃； the Sahara； formerly a marine basin； was peopled by immigrants from the neighbouring countries； and these new animals adapted themselves to the new environment。 He also discusses； among other similar questions； the Isthmus of Panama with regard to its having once been a strait。 From the same author may be quoted the following passage as a strong proof of the new influence： 〃By the radiation of the contemporaneous faunas； each from one centre； whence as the various parts of the world successively were formed and became habitable； they spread and became modified according to the local physical conditions。〃
The 〃multiple〃 origin of each species as advocated by Sclater and Murray； although giving the species a broader basis； suffered from the same difficulties。 There was only one alternative to the old orthodox view of independent creation； namely the bold acceptance of land…connections to an extent for which geological and palaeontological science was not yet ripe。 Those who shrank from either view； gave up the problem as mysterious and beyond the human intellect。 This was the expressed opinion of men like Swainson； Lyell and Humboldt。 Only Darwin had the courage to say that the problem was not insoluble。 If we admit 〃that in the long course of time the individuals of the same species； and likewise of allied species； have proceeded from some one source； then I think all the grand leading facts of geographical distribution are explicable on the theory of migration。。。together with subsequent modification and the multiplication of new forms。〃 We can thus understand how it is that in some countries the inhabitants 〃are linked to the extinct beings which formerly inhabited the same continent。〃 We can see why two areas； having nearly the same physical conditions； should often be inhabited by very different forms of life；。。。and 〃we can see why in two areas； however distant from each other； there should be a correlation； in the presence of identical species。。。and of distinct but representative species。〃 （〃The Origin of Species〃 （1st edition）； pages 408； 409。）
Darwin's reluctance to assume great geological changes； such as a land… connection of Europe with North America； is easily explained by the fact that he restricted himself to the distribution of the present and comparatively recent species。 〃I do not believe that it will ever be proved that within the recent period continents which are now quite separate； h