Dear Sir

I am much obliged for your note & have been greatly interested by the facts you mention of the identical parasites on the same species of birds at immensely remote stations. I am sorry to say I cannot think of any possible means of procuring the parasites of the S. American Mammifers to which you refer. Some surgeon, or officer, interested in Nat. Hist w^d be the only means & I know none now there.

Are you aware whether the same parasites are found on any of our land birds in this country & in N. America. Some of the birds of Europe & N. America appear certainly identical; many form very closely related species or as some would think races: What an interesting investigation w^d be the comparison of the parasites of the closely allied & representative birds of the two countries.

Should you chance to know anything of the parasites of the land-birds of North America, perhaps, sometime you kindly w^d. take the trouble to send me a line, as I am deeply interested in everything connected with geographical distribution, & the differences between species & varieties.— I hope you will turn in your mind the possibility of investigating closely the N. American land-bird-parasites.—

When the same bird in immensely remote countries, has the same parasite, do you never observe some slight difference in colour, size or proportions of such parasites? I have forgotten to answer your question, about the Aperea being identical with the guinea-pig, & I can only answer it by professing entire ignorance & doubt: I certainly sh^d disbelieve it, if you c^d show the parasites were different. How is the parasite of the wolf with the dog, if the latter has one?

I hope you will excuse this long note & believe me dear Sir | Yours very faithfully | C. Darwin