I have read your papers with extreme interest, and I have carefully read
every word of them. (122/1. "Contributions to an Insect Fauna of the
Amazon Valley." (Read March 5th and November 24th, 1860). "Entomological
Soc. Trans." V., pages 223 and 335).) They seem to me to be far richer in
facts of variation, and especially on the distribution of varieties and
subspecies, than anything which I have read. Hereafter I shall re-read
them, and hope in my future work to profit by them and 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 the 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. (122/2. Mr. Bates (page
349) gives reason to believe that the Guiana region should be considered "a
perfectly independent province," and that it has formed a centre "whence
radiated the species which now people the low lands on its borders.")

Would you kindly answer me two or three 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 forms B inhabiting an
intermediate region; does this form B generally exist in equal numbers with
A and C, OR INHABIT AN EQUALLY LARGE AREA? The probability is that you
cannot answer this question, though one of your cases seems to bear on
it...

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 the risk of any small odium in expressing their belief.