This last letter, with others that followed it, directing Meldola’s attention to Weismann’s “Studies in the Theory of Descent,” resulted in the English translation which is so admirably rendered and edited. Many of the later letters are concerned with the progress of this publication. The remarks about dimorphic butterflies referred to Meldola’s observation, that in one of those years in which _Colias edusa_ was extremely abundant, a whole series of forms had been taken transitional between the normal orange female and the white variety _helice_:-- “_Sept. 27_ [1877]. “Down. “MY DEAR SIR,--It is impossible for F. M. [Fritz Müller] to object to anything which you have said in your very interesting little essay.--I just allude to Butterflies preferring certain colours at p. 317 of 2nd Edit^{n.} of the Descent and to the case of the species of Castnia p. 315 which has ornamented hinder wings and displays them, whilst 2 other species have plain hind wings and do not display them. My son, who has charge of my library, returns home to-night and then we will search for Weismann. He gives splendid case of caterpillar with coloured ocelli like true eyes, _and which frightened away birds_. “Yours sincerely, “CH. DARWIN.” The reference in this letter is to Meldola’s paper, “Entomological Notes bearing on Evolution,” soon afterwards published in the _Annals and Magazine of Natural History_, 1878, Vol. I. p. 155. The caterpillar referred to is the well-known larva of the Large Elephant Hawk Moth (_Chærocampa elpenor_). Darwin then wrote a brief note (October 19th, 1877) referring to a number of _Kosmos_ containing an article on “Sexual Selection.” He offered to send the number if it would interest his correspondent. The number was sent, as the succeeding letter shows:-- “_Oct. 22nd [1877]._ “Down. “MY DEAR SIR,--I send Kosmos by this post.... “Prof. Weismann’s address is Freiburg.--I should think he would be glad of translation, and would probably arrange for stereotypes of Plates.--You could say as an introduction that I had lent you his book.--To find a publisher will be perhaps a difficulty. Should it be translated I must beg you to get another copy, as I cannot spare mine for such a length of time.--Wallace sent me his article and I was quite dissatisfied with it.--To explain a peacock’s tail by vital activity seems to me mere verbiage--a mere metaphysical principle. “My dear Sir, yours faithfully, “CH. DARWIN. “It will be a public benefit to bring out a translation.”