Many years ago the late E. Forbes described three closely consecutive beds in a secondary formation, each with representative forms of the same fres-water shells: the case is evidently analogous with that of Hilgendorf ("Ueber Planorbis multiformis im Steinheimer Susswasser-kalk." Monatsbericht of the Berlin Academy, 1866.), but the interesting connecting varieties or links were here absent. I rejoice to think that I formerly said as emphatically as I could, that neither isolation nor time by themselves do anything for the modification of species. Hardly anything in your essay has pleased me so much personally, as to find that you believe to a certain extent in sexual selection. As far as I can judge, very few naturalists believe in this. I may have erred on many points, and extended the doctrine too far, but I feel a strong conviction that sexual selection will hereafter be admitted to be a powerful agency. I cannot agree with what you say about the taste for beauty in animals not easily varying. It may be suspected that even the habit of viewing differently coloured surrounding objects would influence their taste, and Fritz Muller even goes so far as to believe that the sight of gaudy butterflies might influence the taste of distinct species. There are many remarks and statements in your essay which have interested me greatly, and I thank you for the pleasure which I have received from reading it. With sincere respect, I remain, My dear Sir, yours very faithfully, CHARLES DARWIN. P.S.--If you should ever be induced to consider the whole doctrine of sexual selection, I think that you will be led to the conclusion, that characters thus gained by one sex are very commonly transferred in a greater or less degree to the other sex. [With regard to Moritz Wagner's first Essay, my father wrote to that naturalist, apparently in 1868:] Dear and respected Sir,