_9 St. Mark's Crescent, N.W. June 23, 1869._ Dear Darwin,--Thank you very much for the copy of your fifth edition of the "Origin." I have not yet read all the additions, but those I have looked at seem very interesting, though somewhat brief, but I suppose you are afraid of its great and rapid growth. A difficult sexual character seems to me the plumules or battledore scales on the wings of certain families and genera of butterflies, almost invariably changing in form with the species and genera in proportion to other changes, and always constant in each species yet confined to the males, and so small and mixed up with the other scales as to produce no effect on the colour or marking of the wings. How could sexual selection produce them? Your correspondent Mr. Geach is now in England, and if you would like to see him I am sure he would be glad to meet you. He is staying with his brother (address Guildford), but often comes to town. Hoping that you have quite recovered from your accident and that the _great work_ is progressing, believe me, dear Darwin, yours very faithfully, ALFRED R. WALLACE. P.S.--You will perhaps be pleased to hear that German, French, and Danish translations of my "Malay Archipelago" are in progress.--A.R.W. * * * * * _Caerleon, Barmouth, N. Wales. June 25, 1869._ My dear Wallace,--We have been here a fortnight, and shall remain here till the beginning of August. I can say nothing good about my health, and I am so weak that I can hardly crawl half a mile from the house; but I hope I may improve, and anyhow the magnificent view of Cader is enjoyable. I do not know that I have anything to ask Mr. Geach, nor do I suppose I shall be in London till late in the autumn, but I should be particularly obliged, if you have any communication with Mr. Geach, if you would express for me my _sincere_ thanks for his kindness in sending me the very valuable answers on Expression. I wrote some months ago to him in answer to his last letter. I would ask him to Down, but the fatigue to me of receiving a stranger is something which to you would be utterly unintelligible. I think I have heard of the scales on butterflies; but there are lots of sexual characters which quite baffle all powers of even conjecture. You are quite correct, that I felt forced to make all additions to the "Origin" as short as possible. I am indeed pleased to hear, and fully expected, that your Malay work would be known throughout Europe. Oh dear! what would I not give for a little more strength to get on with my work.--Ever yours, C. DARWIN. I wish that you could have told me that your place in the new Museum was all settled. * * * * * _9 St. Mark's Crescent, N.W. October 20, 1869._ Dear Darwin,--I do not know your son's (Mr. George Darwin's) address at Cambridge. Will you be so good as to forward him the enclosed note begging for a little information?