The folly of laying down the law on the strength of the knowledge of the habits of a few species is shown by the study of the movements of American birds. Mr Cooke shows that as a rule "the migration is a synchronous southward movement of the whole species" in autumn, "the different groups of individuals or colonies retaining in general their relative position." The black and white creeper _Mnistitta varia_ breeds from South Carolina to New Brunswick, nesting in the south in April and reaching the northern limits in the middle of May. In the middle of July old and young birds have been seen at Key West, 500 miles south of the breeding range, and towards the end of August they have reached the north coast of South America. The New Brunswick birds cannot be ready to leave before the middle of July, and Mr Cooke allows them fifty days for the trip, bringing them to the Gulf States in September; he argues that this is proof that the earlier migrants must have been birds from the southern part of the range. Black-throated blue warblers, _Dendroica coerulescens_, reach Cuba at about the time that others of the same species are arriving in North Carolina; the first, he concludes, are birds from the southern Alleghanies and the others from northern New England or beyond (20). Other species illustrate the same order which he calls "normal," but show that it is not an invariable rule. Southern-bred Maryland yellow-throats, _Geothlypis trichas_, reside throughout the year in Florida; those in the middle districts of the range migrate for a short distance only, whilst the Newfoundland birds pass over the winter home of their southern relatives to the West Indies. The palm-warblers of the interior of Canada travel 3000 miles to Cuba, passing through the Gulf States early in October; those from north-eastern Canada travel later and slowly and settle in the Gulf States, after a journey of only half the distance. He sums up wisely--"No invariable rule, law, or custom exists in regard to the direction or distance of migration.... Each species presents a separate problem, to be solved for the most part only by patient, pains-taking observation and by the recognition of sub-species."