Dear Sir

I have read your papers with extreme interest & I have carefully read every word of them.¹ They seem to me to be far richer in facts on variation, & especially on the distribution of varieties & subspecies, than anything which I have read. Hereafter I shall reread them, & hope in my future work to profit by them & make use of them. The amount of variation has much surprised me. The analogous variation of distinct species in the same regions strikes me as particularly curious. The greater variability of female sex is new to me. Your Guiana case seems in some degree analogous, as far as plants are concerned, with the modern plains of La Plata, which seem to have been colonised from the north, but the species have been hardly modified.—

I have been particularly struck with your remarks on the Glacial period.² You seem to me to have put the case with admirable clearness & with crushing force. I am quite staggered with the blow & do not know what to think. Of late several facts have turned up leading me to believe more firmly that the Glacial period did affect the Equatorial Regions; but I can make no answer to your argument; & am completely in a cleft stick. By an odd chance I had only a few days ago been discussing this subject, in relation to plants, with D^r. Hooker, who believes to a certain extent; but strongly urged the little apparent extinctions in the Equatorial regions. I stated in a letter some days ago to him, that the Tropics of S. America seem to have suffered less than the Old World.³

There are many perplexing points, temperate plants seem to have migrated far more than animals— Possibly species may have been formed more rapidly within Tropics than one would have expected. I freely confess that you have confounded me: but I cannot yet give up my belief that the Glacial period did to certain extent affect the Tropics.—⁴

Would you kindly answer me 2 or 3 questions if in your power.— When species (A) becomes modified in another region into a well marked form (C), but is connected with it by one (or more) gradational form (B,) inhabiting an intermediate region; does this form (B) generally exist in equal numbers with (A) & (C), or inhabit an equally large area?— The probability is that you cannot answer this question: though one of your cases seem to bear on it.—

Has M^r Baly published on Chrysomelidæ: if so, or when he does, would you give me reference to his paper?⁵

In Butterflies, in which the sexes are differently coloured, is the male or female most beautiful in our eyes? Do you know in Tropics any strictly nocturnal moths with gaudy colours? As with Birds, have you ever noticed that female butterflies make any selection of the male with which they copulate? Do several males pursue same female? Are butterflies attracted by gay colours, as it has been asserted Dragon-flies are. Any authentic facts on the courtship of Butterflies would be most thankfully received & quoted by me. But I can see how very improbable it is that anything sh^d. have been observed.—⁶

You will, I think, be glad to hear that I now often hear of naturalists accepting my views more or less fully: but some are curiously cautious in running risk of any small odium in expressing their belief.

With cordial thanks & respect | Believe me my dear Sir | Yours sincerely | C. Darwin

(Have you received copy of new Edit. of Origin?)⁷