I have been profoundly interested by your essay on Amblystoma ('Umwandlung des Axolotl.'), and think that you have removed a great stumbling block in the way of Evolution. 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 chapter 18 of my 'Variation under Domestication' (volume ii. page 157, of English edition), and these cases illustrate, I think, the sterility of Amblystoma. 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. I think I have heard that the females of Mutilla sometimes have wings. 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 blac-shouldered peacock, the so-called Pavo nigripennis given in my 'Variation under Domestication;' and I might have been bolder, as the variety is in many respects intermediate between the two known species. With much respect, Yours sincerely, CH. DARWIN. THE VIVISECTION QUESTION. [It was in November 1875 that my father gave his evidence before the Royal Commission on Vivisection. (See volume i.) I have, therefore, placed together here the matter relating to this subject, irrespective of date. Something has already been said of my father's strong feeling with regard to suffering both in man and beast. It was indeed one of the strongest feelings in his nature, and was exemplified in matters small and great, in his sympathy with the educational miseries of dancing dogs, or in his horror at the sufferings of slaves. (He once made an attempt to free a patient in a mad-house, who (as he wrongly supposed) was sane. He had some correspondence with the gardener at the asylum, and on one occasion he found a letter from a patient enclosed with one from the gardener. The letter was rational in tone and declared that the writer was sane and wrongfully confined. My father wrote to the Lunacy Commissioners (without explaining the source of his information) and in due time heard that the man had been visited by the Commissioners, and that he was certainly insane. Sometime afterwards the patient was discharged, and wrote to thank my father for his interference, adding that he had undoubtedly been insane, when he wrote his former letter.)