My dear Sir

Will you have the kindness to give me some information on one point? Not long since I was speaking to Mr Wallace about his mimetic butterflies,¹ & I told him of the case of the Rhynchœa, of which the female is more beautiful than the male, with the young resembling the latter.² He answered me that you at Nottingham had advanced this or some such case, & that you had simply explained it by the male being the incubator.³ I should be extremely obliged if you w^d give me any information on this head & allow me to quote you. The subject interests me greatly, as in the 4^th Edit. of the Origin I gave the obvious explanation of female birds not being gaudily coloured &c on account of their incubating;⁴ I knew then of the Rhynchœa but passed over the case from not having space & from its appearing to me quite inexplicable.

I hope that you will forgive me troubling you & believe me my dear Sir | yours sincerely | Charles Darwin

P.S. As I am writing, I will ask one other question, for the chance of your being able to answer it: Does the male black Australian swan, or the black & white S. American Swans, differ from the females in plumage? ie in the intensity of the black, or in the amount of black in the black-necked species?⁵