My dear Sir

I feel much obliged for your never-tiring exertions in obliging me. The last specimen has been quite satisfactory:¹ Verruca acts on the rock in two ways, round the margin & under the middle of the basis: this latter action was unequivocally plain, & suffices in my mind, with all the previous facts known to me, to prove that Verruca acts only on calcareous substances.—² Will you oblige me, by taking the trouble to give me a reference to any book, in which your view of carbonic acid has been given:³ you stated, I think, that this was published, but I have mislaid your letter.

I am glad to perceive that you are progressing in your researches on the metamorphoses of the spider-like Crustacea.—⁴ M^r. Lubbock mentioned to me, when I told him what you had done, that he had seen somewhere (I forget where) something published on this subject; I imagine it probably must have been in some of the late numbers of the Annales des Sciences Naturelles.⁵

With my very sincere thanks for your valuable assistance in regard to Verruca— | Believe me | My dear Sir | Yours sincerely | C. Darwin