The lesson which may be drawn from the experience above stated is to the effect that it is necessary to have a protected field of sufficient area, and in the proper conditions to keep the balance of life which arises from the exchange of relations between species in their normal state. Even in ideal reservations where all invasions are excluded, we should have to expect that from time to time certain forms would disappear, their place perhaps being taken by new species which would arise. Such is the manner of the great procession of life. Probably at least twenty and perhaps a hundred times as many species as are now living on the earth have perished from it, and before the unimaginable goal is attained as many others may pass away. Our task with the refuges would be to keep the death of the specific inhabitants to the natural and wholesome rate that is determined by the endless struggle for existence. It is impracticable at the present time to devise a scheme for refuge stations in other countries than our own; it is evident, however, that these would have to be numerous and widely distributed. A glance at a map showing the political distribution of the lands will make it evident, however, that within the holdings of the British, French, German, Dutch, and Russian governments there are large areas which might, without evident loss of considerable economic values, immediate or prospective, be turned to such uses, and that these reservations would probably include nearly all that would be required to preserve the most important samples of the primitive life. Some of them, as for instance those intended to retain the large tropical animals in their natural state, would have to be as imperial in their areas as the Yellowstone Park, but these would lie in realms which have no present value to our own race and are scantily inhabited by the indigenous peoples.