My dear Sir

I have come here for a few weeks for a little change & rest.¹ Just as I was leaving home I received your first note & yesterday a second; & both are most interesting & valuable to me.—²

That is a very curious observation about the Gold-finches beak, but one would hardly like to trust it without measurement or comparison of the beaks of several male & female birds; for I do not understand that you yourself assert that the beak of the male is sensibly longer than that of the female.—³ If you come across any acute bird-catchers (I do not mean to ask you to go after them); I wish you would ask what is their impression on the relative numbers of the sexes of any birds, which they habitually catch, & whether some years males are more numerous & some years females.—

I see that I must trust to analogy, (an unsafe support) for sexual selection in regard to colour in Butterflies. You speak of the Brimstone Butterfly & genus Edusa (I forget what this is, & have no books here, unless it it is Colias) not opening their wings;⁴ in one of my notes to M^r. Stainton I asked him, (but he could or did not answer) whether Butterflies such as the Fritillaries with wings bright beneath & above, opened & shut their wings more than Vanessæ most of which I think are obscure on the under surface.⁵

That is a most curious observation about the red underwing moth & the Robin;⁶ & strongly supports a suggestion, (which I thought hardly credible) of A. R. Wallace viz that the immense wings of some exotic Lepidoptera served as a protection from difficulty of Birds seizing them. I will probably quote your case.—⁷

No doubt D^r Hooker collected the Kerguelen moth, for I remember he told me of the case, when I suggested in the Origin the explanation of the Coleoptera of Madeira being apterous; but he did not know what had become of the specimens.—⁸

I am quite delighted to hear that you are observing coloured Birds, though the probability, I suppose, will be that no sure result will be gained.—⁹ I am accustomed with my numerous experiments with plants to be well satisfied if I get any good result in one case out of five.—

With most sincere thanks for your great kindness— | My dear Sir | Yours very sincerely | Ch. Darwin

You will not be able to read all my book—too much detail— some of chaptr in 2^d Vol. are curious I think.—¹⁰

If any man wants to gain a good opinion of his fellow men, he ought to do what I am doing   pester them with letters.—