With respect to the letters which follow the first eight, both sides of the correspondence, with few exceptions, have been brought together. Some of the letters have already appeared in "The Life and Letters of Charles Darwin" and "More Letters," others in "My Life," by A.R. Wallace, whilst many have not before been published. Some of these letters, in themselves, have little more than ephemeral interest, and parts of other letters could have been eliminated, from the point of view of lightening this volume and of economising the reader's attention. But I decided, with the fullest approval of the Wallace and Darwin families, that the letters of these illustrious correspondents should be here presented as a whole, without mutilation. [Illustration: FACSIMILE OF INSCRIPTION BY WALLACE ON THE ENVELOPE IN WHICH HE KEPT THE FIRST EIGHT LETTERS HE RECEIVED FROM DARWIN.] Many of the notes of explanation to the Wallace letters have been gathered from his own writings, and are mainly in his own words, and in such cases the reader has the advantage of perusing letters annotated by their author, while most of the notes to the Darwin letters are by Sir F. Darwin. * * * * * LETTER I C. DARWIN to A.R. WALLACE _Down, Bromley, Kent, May 1, 1857._ My dear Sir,--I am much obliged for your letter of Oct. 10th from Celebes, received a few days ago: in a laborious undertaking, sympathy is a valuable and real encouragement. By your letter, and even still more by your paper in the _Annals_,[28] a year or more ago, I can plainly see that we have thought much alike and to a certain extent have come to similar conclusions. In regard to the paper in the _Annals_, I agree to the truth of almost every word of your paper; and I daresay that you will agree with me that it is very rare to find oneself agreeing pretty closely with any theoretical paper; for it is lamentable how each man draws his own different conclusions from the very same fact. This summer will make the twentieth year (!) since I opened my first note-book on the question how and in what way do species and varieties differ from each other. I am now preparing my work for publication, but I find the subject so very large, that though I have written many chapters, I do not suppose I shall go to press for two years. I have never heard how long you intend staying in the Malay Archipelago; I wish I might profit by the publication of your Travels there before my work appears, for no doubt you will reap a large harvest of facts.