[The following letter refers to Mr. Bates's paper, "Contributions to an Insect Fauna of the Amazon Valley," in the 'Transactions of the Entomological Society,' vol.5, N.S. (The paper was read November 24, 1860.) Mr. Bates points out that with the return, after the glacial period, of a warmer climate in the equatorial regions, the "species then living near the equator would retreat north and south to their former homes, leaving some of their congeners, slowly modified subsequently... to re-people the zone they had forsaken." In this case the species now living at the equator ought to show clear relationship to the species inhabiting the regions about the 25th parallel, whose distant relatives they would of course be. But this is not the case, and this is the difficulty my father refers to. Mr. Belt has offered an explanation in his 'Naturalist in Nicaragua' (1874), page 266. "I believe the answer is that there was much extermination during the glacial period, that many species (and some genera, etc., as, for instance, the American horse), did not survive it... but that a refuge was found for many species on lands now below the ocean, that were uncovered by the lowering of the sea, caused by the immense quantity of water that was locked up in frozen masses on the land."] CHARLES DARWIN TO J.D. HOOKER. Down, 27th [March 1861]. My dear Hooker, I had intended to have sent you Bates's article this very day. I am so glad you like it. I have been extremely much struck with it. How well he argues, and with what crushing force against the glacial doctrine. I cannot wriggle out of it: I am dumbfounded; yet I do believe that some explanation some day will appear, and I cannot give up equatorial cooling. It explains so much and harmonises with so much. When you write (and much interested I shall be in your letter) please say how far floras are generally uniform in generic character from 0 to 25 degrees N. and S. Before reading Bates, I had become thoroughly dissatisfied with what I wrote to you. I hope you may get Bates to write in the 'Linnean.' Here is a good joke: H.C. Watson (who, I fancy and hope, is going to review the new edition (third edition of 2000 copies, published in April, 1861.) of the 'Origin') says that in the first four paragraphs of the introduction, the words "I," "me," "my," occur forty-three times! I was dimly conscious of the accursed fact. He says it can be explained phrenologically, which I suppose civilly means, that I am the most egotistically self-sufficient man alive; perhaps so. I wonder whether he will print this pleasing fact; it beats hollow the parentheses in Wollaston's writing. _I_ am, MY dear Hooker, ever yours, C. DARWIN. P.S.--Do not spread this pleasing joke; it is rather too biting. CHARLES DARWIN TO J.D. HOOKER. Down, [April] 23? [1861].