My dear Sir

I am rejoiced to hear that your eye-sight is somewhat better; but I fear that work with the microscope is still out of your power.¹ I have often thought with sincere sympathy how much you must have suffered from your grand line of embryological research having been stopped.² It was very good of you to use your eyes in writing to me. I have just received your essay; but as I am now staying in London for the sake of rest, and as german is at all times very difficult to me, I shall not be able to read your essay for some little time. I am however very curious to learn what you have to say on isolation and on periods of variation.³ I thought much about isolation when I wrote in Chap. IV on the circumstances favourable to Nat. Selection.⁴ No doubt there remains an immense deal of work to do on Artbildung.⁵ I have only opened a path for others to enter, and in the course of time, to make a broad and clear high-road. I am especially glad that you are turning your attention to sexual selection. I have in this country hardly found any naturalists who agree with me on this subject, even to a moderate extent. They think it absurd that a female bird should be able to appreciate the spendid plumage of the male; but it would take much to persuade me that the pea-cock does not spread his gorgeous tail in the presence of the female in order to fascinate or excite her. The case no doubt is much more difficult with insects. I fear that you will find it difficult to experiment on diurnal Lepidoptera in confinement, for I have never heard of any of these breeding in this state.⁶ I was extremely pleased at hearing from Fritz Müller that he liked my chapter on Lepidoptera in the Descent of Man more than any other part, excepting the chapter on morals.⁷

With the most sincere respect and good wishes for your improved eyesight, I remain, my dear Sir | Yours very faithfully | Ch. Darwin