As my book has failed to explain my meaning, it would be hopeless to attempt it in a letter. You speak in the early part of your letter, and at page 9, as if I had said that Natural Selection was the sole agency of modification, whereas I have over and over again, ad nauseam, directly said, and by order of precedence implied (what seems to me obvious) that selection can do nothing without previous variability (see pages 80, 108, 127, 468, 469, etc.), "nothing can be effected unless favourable variations occur." I consider Natural Selection as of such high importance, because it accumulates successive variations in any profitable direction, and thus adapts each new being to its complex conditions of life. The term "selection," I see, deceives many persons, though I see no more reason why it should than elective affinity, as used by the old chemists. If I had to rewrite my book, I would use "natural preservation" or "naturally preserved." I should think you would as soon take an emetic as re-read any part of my book; but if you did, and were to erase selection and selected, and insert preservation and preserved, possibly the subject would be clearer. As you are not singular in misunderstanding my book, I should long before this have concluded that my brains were in a haze had I not found by published reviews, and especially by correspondence, that Lyell, Hooker, Asa Gray, H.C. Watson, Huxley, and Carpenter, and many others, perfectly comprehend what I mean. The upshot of your remarks at page 11 is that my explanation, etc., and the whole doctrine of Natural Selection, are mere empty words, signifying the "order of nature." As the above-named clear-headed men, who do comprehend my views, all go a certain length with me, and certainly do not think it all moonshine, I should venture to suggest a little further reflection on your part. I do not mean by this to imply that the opinion of these men is worth much as showing that I am right, but merely as some evidence that I have clearer ideas than you think, otherwise these same men must be even more muddle-headed than I am; for they have no temptation to deceive themselves. In the forthcoming September (110/3. "American Journal of Science and Arts," September 1860, "Design versus Necessity," reprinted in Asa Gray's "Darwiniana," 1876, page 62.) number of the "American Journal of Science" there is an interesting and short theological article (by Asa Gray), which gives incidentally with admirable clearness the theory of Natural Selection, and therefore might be worth your reading. I think that the theological part would interest you.
You object to all my illustrations. They are all necessarily conjectural, and may be all false; but they were the best I could give. The bear case (110/4. "Origin of Species," Edition I., page 184. See Letter 120.) has been well laughed at, and disingenuously distorted by some into my saying that a bear could be converted into a whale. As it offended persons, I struck it out in the second edition; but I still maintain that there is no especial difficulty in a bear's mouth being enlarged to any degree useful to its changing habits,--no more difficulty than man has found in increasing the crop of the pigeon, by continued selection, until it is literally as big as the whole rest of the body. If this had not been known, how absurd it would have appeared to say that the crop of a bird might be increased till it became like a balloon!
With respect to the ostrich, I believe that the wings have been reduced, and are not in course of development, because the whole structure of a bird is essentially formed for flight; and the ostrich is essentially a bird. You will see at page 182 of the "Origin" a somewhat analogous discussion. At page 450 of the second edition I have pointed out the essential distinction between a nascent and rudimentary organ. If you prefer the more complex view that the progenitor of the ostrich lost its wings, and that the present ostrich is regaining them, I have nothing to say in opposition.