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Show 646 MR. H. J. ELWES ON THE GEOGRAPHICAL [June 17, The attempt to account for the various facts which are here and there brought to light is a task far beyond m y power or inclination, more especially as I do not see h ow we can speculate with much advantage on the causes which have influenced the distribution of birds whilst our ignorance of the distribution of other animals is so great. O n the m a p (Plate LI.) to which I beg leave to draw your attention, I have shown the ornithological divisions into which I believe Asia may be divided; and though, as is obvious, a hard and fast line can never be drawn between the different regions and subregions, yet in some places (as, for instance, "Wallace's line" and the Himalaya mountains) they are separated by a distance which is on the map hardly appreciable. Ihe connexion between climate, physical geography, and ornithology is m u c h closer in Asia than would be supposed by any one w ho had not travelled there. All over the Indo-Malay region, wherever hills exceeding 3000 or 4000 feet high are found, a moister climate and more luxuriant vegetation is sure to be accompanied by a corresponding change in the birds. So much is this the case that wherever in India, South China, and the Indo-Chinese countries an elevation of 4000 feet is reached, some of the birds characteristic of the Himalaya are almost sure to be found. Another point that has struck m e is that in Asia almost every genus of birds found in Europe is represented by some, and often by a greater number of similar or allied species. This would seem to show, what I believe is equally true of plants and animals, that the birds of Europe have been derived from the east; and though we have got into a habit of considering many genera of birds especially characteristic of Europe, it is only because we know so much less of their distribution in Asia. This of course applies principally to the temperate regions of Northern and Central Asia; but I think it impossible to gain a correct idea of European ornithology without a considerable knowledge of the whole Palaearctic avifauna. A large number of genera and families found in Tropical Asia are also common to Africa; and though I do not think we can place the two continents in the same zoological region (as M r . Murray has done in his work, * The Geographical Distribution of Mammalia'), yet I believe a careful comparison of generic forms from Africa and Asia would result in the union of several genera which are now separated. One of m y greatest difficulties has been the want of a really reliable work on the genera of birds ; for though I have in most cases followed the arrangement of M r . Gray's * Hand-list,' I have often found that the uncertainty of classification which prevails has diminished the confidence which I should otherwise have had in some portions of m y work. I will now endeavour to show how far the conclusions I have formed are borne out by facts, and hope that m y attempt to deal in a connected manner with so vast a subject will be found to contain the elements of truth. |