My dear Wallace,--I am much obliged for your photograph, for I have lately set up a scientific album; and for the papers, which I will read before long. I enclose my own photo, taken by my son, and I have no other. I fear it will be a long time before I shall be able to sit to a photographer, otherwise I should be happy to sit to Mr. Sims. Thanks for information about the Aru pig, which will make me very cautious. It is a perplexing case, for Nathusius says the skull of the Aru resembles that of the Chinese breed, and he thinks that _Sus papuensis_ has been founded on a young skull; D. Blainville stating that an old skull from New Guinea resembles that of the wild pigs of Malabar, and these belong to the _S. scrofa_ type, which is different from the Chinese domestic breed. The latter has not been found in a wild condition.--Believe me, dear Wallace, yours very sincerely, CH. DARWIN. * * * * * _9 St. Mark's Crescent, Regent's Park, N.W. Sept. 18, 1865._ Dear Darwin,--I should have written before to thank you for the copy of your paper on climbing plants, which I read with great interest; I can imagine how much pleasure the working out must have given you. I was afraid you were too ill to make it advisable that you should be bothered with letters. I write now, in hopes you are better, to communicate a curious case of _variation_ becoming at once _hereditary_, which was brought forward at the British Association. I send a note of it on the other side, but if you would like more exact particulars, with names and dates and a drawing of the bird, I am sure Mr. O'Callaghan would send them to you. I hope to hear that you are better, and that your new book is really to come out next winter.--Believe me yours very faithfully, ALFRED R. WALLACE. NOTE.--Last spring Mr. O'Callaghan was told by a country boy that he had seen a blackbird with a topknot; on which Mr. O'C. very judiciously told him to watch it and communicate further with him. After a time the boy told him he had found a blackbird's nest, and had seen this crested bird near it and believed he belonged to it. He continued watching the nest till the young were hatched. After a time he told Mr. O'C. that two of the young birds seemed as if they would have topknots. He was told to get one of them as soon as it was fledged. However, he was too late, and they left the nest, but luckily he found them near and knocked one down with a stone, which Mr. O'C. had stuffed and exhibited. It has a fine crest, something like that of a Polish fowl, but _larger_ in proportion to the bird, and very regular and well formed. The male must have been almost like the Umbrella bird in miniature, the crest is so large and expanded.--A.R.W. * * * * * _Down, Bromley, Kent, S.E. September 22, 1865._