Will our young July thrush remain in England or will it join one of these streams, and if so which? We do not know yet. I repeat "yet," for the study of races, sub-species or local variations is commanding more and more attention; the patient work of the "splitters," scorned by the old school of "lumpers," will eventually solve many of the problems of to-day. The ancients--a usefully ambiguous term--realised that birds migrated; our immediate forefathers of two or three centuries ago realised that certain birds vanished in winter and wondered how; and within modern times the phenomena of migration, the "mystery of mysteries," has been the subject of much study, speculation, and literary exposition. Indeed a full bibliography of migration would be a considerable volume. Even workers within the last few years have declared that certain phenomena were beyond human understanding, only to be explained by instinct, a word capable of most varied interpretation. In truth there is much to learn, much to which we must still answer--we do not know; but the speculative theory of yesterday is now either myth or fact, and the theory of to-day may be proved true and add something to the data of which knowledge is built. The wildest speculations, based on slender locally ascertained facts or on no foundation whatever except the fertility of the brain, have been offered as solutions of the mysteries; the literature of migration is a jumble of contradictions. John Legg, in 1780, said "In relating so many instances of unparalleled credulity, I confess I cannot suppress the irascible passion" (33), and Herr Otto Herman, only a few years ago, pointing out the ingenious dogmas "void of every firm foundation," says that "really it is a field in which every thinking ornithologist may create new theses to any extent and more or less incredible" (31). Herr Herman's system of "ornithophænology," the accumulation of substantiated observations and facts, will not prove everything, but his work in Hungary, that of Dr Merriam and Mr Cooke in America, and of Mr W. Eagle Clarke in Britain, each aided by a numerous band of careful workers, are striking examples of what can be accomplished. Whatever errors future enlightenment may show in their conclusions their ascertained facts will remain positive knowledge; theirs is not what Herr Herman himself described as "pretended authority." In order to grasp the problems of migration it is necessary to get rid of the puerile and insular aspect of the subject, namely that migrants are merely those birds which come to us, like the swallow and cuckoo in the spring, and those, like the fieldfare and brambling, which visit us in winter but are not with us in summer. The complication of the subject may be demonstrated by a rough classification of the migrants to be observed in the British Islands. Arbitrary grouping of the members of an avifauna is only for general convenience; many species are represented in more than one group.