Also MS. of hybridism and pigeons, which will just weary you to death. I will call myself for or send a servant for the MS. and bones whenever you have done with them; but do not hurry. You have hit on the exact plan, which, on the advice of Lyell, Murray, etc., I mean to follow--viz., bring out separate volumes in detail--and I shall begin with domestic productions; but I am determined to try and [work] very slowly, so that, if possible, I may keep in a somewhat better state of health. I had not thought of illustrations; that is capital advice. Farewell, my good and admirable agent for the promulgation of damnable heresies! LETTER 86. TO L. HORNER. Down, December 23rd [1859]. I must have the pleasure of thanking you for your extremely kind letter. I am very much pleased that you approve of my book, and that you are going to pay me the extraordinary compliment of reading it twice. I fear that it is tough reading, but it is beyond my powers to make the subject clearer. Lyell would have done it admirably. You must enjoy being a gentlemen at your ease, and I hear that you have returned with ardour to work at the Geological Society. We hope in the course of the winter to persuade Mrs. Horner and yourself and daughters to pay us a visit. Ilkley did me extraordinary good during the latter part of my stay and during my first week at home; but I have gone back latterly to my bad ways, and fear I shall never be decently well and strong. P.S.--When any of your party write to Mildenhall I should be much obliged if you would say to Bunbury that I hope he will not forget, whenever he reads my book, his promise to let me know what he thinks about it; for his knowledge is so great and accurate that every one must value his opinions highly. I shall be quite contented if his belief in the immutability of species is at all staggered. LETTER 87. TO C. LYELL. (87/1. In the "Origin of Species" a section of Chapter X. is devoted to "The succession of the same types within the same areas, during the late Tertiary period" (Edition I., page 339). Mr. Darwin wrote as follows: "Mr. Clift many years ago showed that the fossil mammals from the Australian caves were closely allied to the living marsupials of that continent." After citing other instances illustrating the same agreement between fossil and recent types, Mr. Darwin continues: "I was so much impressed with these facts that I strongly insisted, in 1839 and 1845, on this 'law of the succession of types,' on 'this wonderful relationship in the same continent between the dead and the living.' Professor Owen has subsequently extended the same generalisation to the mammals of the Old World.") Down, [December] 27th [1859].