Page:The Zoologist, 4th series, vol 1 (1897).djvu/399

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is a very interesting volume on a question of transcendent interest to ornithologists, to whom the problem of the migration of birds is as difficult of solution as is that of mimicry by entomologists. Avine migration as treated by Mr. Dixon derives a freshness by the perfectly original—almost revolutionary—method by which it is sought to be explained. The old teachings as to the part played by the important factors of change of climate and scarcity of food, and the theory of Polar dispersal, are quite discarded, and the author's main contention is that "the grand centre of Life's dispersal across the globe is an equatorial one, and that, from those regions where the greatest stability of climate and the most favourable conditions for the development of animal and vegetable forms are to be found, Life in two grand streams has flowed towards the poles." Glacial epochs are considered as exterminating influences and not as dispersing agencies, and on their cessation the areas over which they have exercised their icy and lifeless sway are again colonized from Nature's headquarters in the equatorial regions. Then again the old theory of avine hibernation, so generally considered as belonging to the limbo of forgotten suggestions, is not only revived, but its scanty evidence also amply discussed, and the conclusion stated that—"Strange, nay almost incredible as avine hibernation is, however, it must always be remembered that the evidence against it is purely negative; and that, although it has not yet been sufficiently established to satisfy the sceptical science of to-day, it has never been refuted."

With all the painstaking investigation now being pursued on the subject of migration by enthusiastic ornithologists, the industrious tabulation of their facts, and the critical collocation