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una and flora and to the present configuration of land and water。 Next came Oceanography concerned with the depths of the seas； their currents and temperatures； then enquiries into climatic changes； culminating in irreconcilable astronomical hypotheses as to glacial epochs； theories about changes of the level of the seas； mainly from the point of view of the physicist and astronomer。 Then came more and more to the front the importance of the geological record； hand in hand with the palaeontological data and the search for the natural affinities； the genetic system of the organisms。 Now and then it almost seems as if the biologists had done their share by supplying the problems and that the physicists and geologists would settle them； but in reality it is not so。 The biologists not only set the problems； they alone can check the offered solutions。 The mere fact of palms having flourished in Miocene Spitzbergen led to an hypothetical shifting of the axis of the world rather than to the assumption； by way of explanation； that the palms themselves might have changed their nature。 One of the most valuable aids in geological research； often the only means for reconstructing the face of the earth in by…gone periods； is afforded by fossils； but only the morphologist can pronounce as to their trustworthiness as witnesses； because of the danger of mistaking analogous for homologous forms。 This difficulty applies equally to living groups； and it is so important that a few instances may not be amiss。
There is undeniable similarity between the faunas of Madagascar and South America。 This was supported by the Centetidae and Dendrobatidae； two entire 〃families；〃 as also by other facts。 The value of the Insectivores； Solenodon in Cuba； Centetes in Madagascar； has been much lessened by their recognition as an extremely ancient group and as a case of convergence； but if they are no longer put into the same family； this amendment is really to a great extent due to their widely discontinuous distribution。 The only systematic difference of the Dendrobatidae from the Ranidae is the absence of teeth； morphologically a very unimportant character； and it is now agreed； on the strength of their distribution； that these little arboreal； conspicuously coloured frogs； Dendrobates in South America； Mantella in Madagascar； do not form a natural group； although a third genus； Cardioglossa in West Africa； seems also to belong to them。 If these creatures lived all on the same continent； we should unhesitatingly look upon them as forming a well…defined； natural little group。 On the other hand the Aglossa； with their three very divergent genera； namely Pipa in South America； Xenopus and Hymenochirus in Africa； are so well characterised as one ancient group that we use their distribution unhesitatingly as a hint of a former connection between the two continents。 We are indeed arguing in vicious circles。 The Ratitae as such are absolutely worthless since they are a most heterogeneous assembly； and there are untold groups； of the artificiality of which many a zoo… geographer had not the slightest suspicion when he took his statistical material； the genera and families； from some systematic catalogues or similar lists。 A lamentable instance is that of certain flightless Rails； recently extinct or sub…fossil； on the isalnds of Mauritius； Rodriguez and Chatham。 Being flightless they have been used in support of a former huge Antarctic continent； instead of ruling them out of court as Rails which； each in its island； have lost the power of flight； a process which must have taken place so recently that it is difficult； upon morphological grounds； to justify their separation into Aphanapteryx in Mauritius； Erythromachus in Rodriguez and Diaphorapteryx on Chatham Island。 Morphologically they may well form but one genus； since they have sprung from the same stock and have developed upon the same lines； they are therefore monogenetic： but since we know that they have become what they are independently of each other （now unlike any other Rails）； they are polygenetic and therefore could not form one genus in the old Darwinian sense。 Further； they are not a case of convergence； since their ancestry is not divergent but leads into the same stratum。
THE RECONSTRUCTION OF THE GEOGRAPHY OF SUCCESSIVE EPOCHS。
A promising method is the study by the specialist of a large； widely distributed group of animals from an evolutionary point of view。 Good examples of this method are afforded by A。E。 Ortmann's （〃The geographical distribution of Freshwater Decapods and its bearing upon ancient geography〃； 〃Proc。 Amer。 Phil。 Soc。〃 Vol。 41； 1902。） exhaustive paper and by A。W。 Grabau's 〃Phylogeny of Fusus and its Allies〃 （〃Smithsonian Misc。 Coll。〃 44； 1904。） After many important groups of animals have been treated in this wayas yet sparingly attemptedthe results as to hypothetical land…connections etc。 are sure to be corrective and supplementary； and their problems will be solved； since they are not imaginary。
The same problems are attacked； in the reverse way； by starting with the whole fauna of a country and thence； so to speak； letting the research radiate。 Some groups will be considered as autochthonous； others as immigrants； and the directions followed by them will be inquired into； the search may lead far and in various directions； and by comparison of results； by making compound maps； certain routes will assume definite shape； and if they lead across straits and seas they are warrants to search for land…connections in the past。 （A fair sample of this method is C。H。 Eigenmann's 〃The Freshwater Fishes of South and Middle America〃； 〃Popular Science Monthly〃； Vol。 68； 1906。） There are now not a few maps purporting to show the outlines of land and water at various epochs。 Many of these attempts do not tally with each other； owing to the lamentable deficiencies of geological and fossil data； but the bolder the hypothetical outlines are drawn； the better； and this is preferable to the insertion of bays and similar detail which give such maps a fallacious look of certainty where none exists。 Moreover it must be borne in mind that； when we draw a broad continental belt across an ocean； this belt need never have existed in its entirety at any one time。 The features of dispersal； intended to be explained by it； would be accomplished just as well by an unknown number of islands which have joined into larger complexes while elsewhere they subsided again： like pontoon…bridges which may be opened anywhere； or like a series of superimposed dissolving views of land and sea…scapes。 Hence the reconstructed maps of Europe； the only continent tolerably known； show a considerable number of islands in puzzling changes； while elsewhere； e。g。 in Asia； we have to be satisfied with sweeping generalisations。
At present about half…a…dozen big connections are engaging our attention； leaving as comparatively settled the extent and the duration of such minor 〃bridges〃 as that between Africa and Madagascar； Tasmania and Australia； the Antilles and Central America； Europe and North Africa。 （Not a few of those who are fascinated by； and satisfied with； the statistical aspect of distr