My Dear M^r Darwin

The discovery of signs of a glacial period in Miocene times is very remarkable as I dare say you have thought, in as much as the whole tertiary ⁠⟨⁠ep⁠⟩⁠och has been always considered a time of greater warmth than the present in the Northern Hemisphere. But if it turns out a cold epoch intervened in middle of the tertiary it would only compel us to enlarge the lapse of time allowed to the whole.¹

I have just received the German monograph on Chilian Carabi.² It is very complete. The author is of high reputation. He concludes that the 11 species form only a section of the genus although very closely allied amongst themselves & distinct as a body from all Carabi of the Northern Hemisphere. He anticipates no future discovery to modify ⁠⟨⁠current⁠⟩⁠ conclusions on the Geographical distribution of the genus. No Carabus has been found within the tropics & none beyond the Southern tropic in Eastern Hemisphere   He goes into many inquiries arising out of the subject but strange to say does not start the question “Whence came these isolated Chilian Carabi?”

I never thought of modifications in horny genital apparatus of closely-allied Chrysomelæ being a difficulty ⁠⟨⁠for the⁠⟩⁠ theory.³ Quite the contrary it see⁠⟨⁠ms that⁠⟩⁠ they were a strong support of it. M^r ⁠⟨⁠Baly⁠⟩⁠ has found that an English Chr⁠⟨⁠ysomela⁠⟩⁠ believed on other grounds to be a ⁠⟨⁠    ⁠⟩⁠ in these organs from its supp⁠⟨⁠  ⁠⟩⁠ ⁠⟨⁠    ⁠⟩⁠⁴   He therefore again separates it & ⁠⟨⁠there⁠⟩⁠ is an end of the matter. Like many other ⁠⟨⁠natur⁠⟩⁠alists who aim only at separating species neatly in their collections & monographs, M^r Baly never thinks of the possibility of gradual modification & consequently never looks in Nature for it. I believe, as regards the total specific form, $\frac{3}{4}$ ^ths of the species in all large groups will be found, when specimens are collected over a wide area, to be incapable of sharp definition from their nearest allies.

⁠⟨⁠    ⁠⟩⁠ modifications have scarcely ever been ⁠⟨⁠called for⁠⟩⁠, even in the whole specific char⁠⟨⁠acter or⁠⟩⁠ special organs. Mr Janson,⁵ an ⁠⟨⁠entom⁠⟩⁠ologist tells me there is a difference ⁠⟨⁠in genital⁠⟩⁠ apparatus between two English ⁠⟨⁠Carabi⁠⟩⁠ C. hybrida & C. maritima. Now ⁠⟨⁠modern⁠⟩⁠ ⁠⟨⁠en⁠⟩⁠tomologists, on the most conclusive ⁠⟨⁠evidenc⁠⟩⁠e have re-united these two. It appears ⁠⟨⁠h⁠⟩⁠owever the two are more distinct in England than on the Continent! This is what I should expect from observations on S. American insects. There is a gradual divergence amongst varieties of a species over a wide area. Who would think of examining the genital apparatus through all the graduated series of vars. of these Cicindelæ?

Thanks for the copy of “Orchids”. I have read it through with great pleasure.⁶ It is very clear.— In Ann. Nat. Hist. for June you will see a note of mine on a new way of regarding local varieties⁷   I have sent in an application for British Museum. situation but it will be of little use.⁸ Something else may turn up soon

Yours sincerely   H W Bates

I go tomorrow to London, for three days chiefly to see the artist about finishing the plates for Linnean Transactions.⁹ I shall call on Murray.¹⁰ Can I do anything for you. The address 43 Harwood St Hampstead road will find me.