240 THE SCIENTIFIC MONTHLY
The laws, then, which govern the smaller, seasonal migrants seem so undoubted and severe that one can not fail to perceive that more com- plete and far-gathered data directed toward the problem of their begin- ning in season and in prehistoric time may even shed an additional light upon the very origin of bird movements. For, notwithstanding the voluminous literature which has grown up about the feathered migrants and the theories of climatic change initiated by the Ice Ag<Q as respon- sible for their annual flux and flow, these annual adventures still remain one of the most inexplicable and marvelous manifestations of animal life. It is equally true that the application of marking and tracing methods to insects (which have long been the practise of the bird stu- dent) will now be made possible, owing to the fact that certain of the eastern routes are clearly defined, allowing the naturalist to determine the extent of the southward movement in each species, the place and manner of the winter sojourn, and, also, how many of the northward- moving migrants of spring are new generations bred in that warmer region, and how many are, in very truth, the same individual travelers which set out upon their long, southward journey in the autumn.
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