My dear Sir

I have been profoundly interested by your essay on Amblystoma, and think that you have removed a great stumbling block in the way of evolution.¹ I once thought of reversion in this case; but in a crude and imperfect manner. I write now to call your attention to the sterility of moths when hatched out of their proper season: I give references in Chap. 18 of my Variation under Domestication (Vol. 2 p. 157 of English Edit.) and these cases illustrate, I think, the sterility of Amblystoma.² Would it not be worth while to examine the reproductive organs of those individuals of wingless Hemiptera which occasionally have wings, as in the case of the bed-bug.³ I think I have heard that the females of Mutilla sometimes have wings.⁴ These cases must be due to reversion. I dare say many anomalous cases will be hereafter explained on the same principle.

I hinted at this explanation in the extraordinary case of the black-shouldered peacock, the so-called Pavo nigripennis, given in my Var. under Domest.; and I might have been bolder, as the var. is in many respects intermediate between the two known species.⁵

With much respect | Yours sincerely, | Ch. Darwin

P.S.— There is a more appropriate case among Plants. Peloric flowers must be considered as cases of reversion to a symmetrical form; and many of these flowers are quite sterile and others quite fertile: see Chapt. 18 of Dom. under Var. in section Monstrosities as a cause of Sterility.⁶ I quote Godron on Corydalis solida; but he has since found other peloric flowers on this same species fertile; so sterility is variable in same species; so indeed with Pelargonium, as I show.—⁷