Dr. Günther gave me much valuable information on the classification of reptiles, marking on my lists the best established and most natural genera, and referring me to reliable sources of information. I am also greatly indebted to the following gentlemen for detailed information on special subjects:-- To Sir Victor Brooke, for a MS. arrangement of the genera of Bovidæ, with the details of their distribution: To Mr. Dresser, for lists of the characteristic birds of Northern and Arctic Europe: To Dr. Hooker, for information on the colours and odours of New Zealand plants: To Mr. Kirby, for a list of the butterflies of Chili: To Professor Mivart, for a classification of the Batrachia, and an early proof of his article on "Apes" in the Encyclopedia Britannica: To Mr. Salvin, for correcting my list of the birds of the Galapagos, and for other assistance: To Mr. Sharpe, for MS. lists of the birds of Madagascar and the Cape Verd Islands: To Canon Tristram, for a detailed arrangement of the difficult family of the warblers,--Sylviidæ: To Viscount Walden, for notes on the systematic arrangement of the Pycnonotidæ and Timaliidæ, and for an early proof of his list of the birds of the Philippine Islands. I also have to thank many naturalists, both in this country and abroad, who have sent me copies of their papers; and I trust they will continue to favour me in the same manner. An author may easily be mistaken in estimating his own work. I am well aware that this first outline of a great subject is, in parts, very meagre and sketchy; and, though perhaps overburthened with some kinds of detail, yet leaves many points most inadequately treated. It is therefore with some hesitation that I venture to express the hope that I have made some approach to the standard of excellence I have aimed at;--which was, that my book should bear a similar relation to the eleventh and twelfth chapters of the "Origin of Species," as Mr. Darwin's "Animals and Plants under Domestication" does to the first chapter of that work. Should it be judged worthy of such a rank, my long, and often wearisome labours, will be well repaid. MARCH, 1876. CONTENTS OF THE FIRST VOLUME. PART I. THE PRINCIPLES AND GENERAL PHENOMENA OF DISTRIBUTION. CHAPTER I. INTRODUCTORY. CHAPTER II. THE MEANS OF DISPERSAL AND THE MIGRATIONS OF ANIMALS.