In the same number of the _Popular Science Review_, and immediately following the review of Mr. Darwin’s book, there is a review of “Evolution, Old and New.” The writer of this review quotes the passage about mental anachronism as quoted by the reviewer in the _Pall Mall Gazette_, and adds immediately: “This anachronism has been committed by Mr. Samuel Butler in a . . . little volume now before us, and it is doubtless to this, _which appeared while his own work was in progress_ [italics mine] that Dr. Krause alludes in the foregoing passage.” Considering that the editor of the _Popular Science Review_ and the translator of Dr. Krause’s article for Mr. Darwin are one and the same person, it is likely the _Popular Science Review_ is well informed in saying that my book appeared before Dr. Krause’s article had been transformed into its present shape, and that my book was intended by the passage in question. Unable to see any way of escaping from a conclusion which I could not willingly adopt, I thought it best to write to Mr. Darwin, stating the facts as they appeared to myself, and asking an explanation, which I would have gladly strained a good many points to have accepted. It is better, perhaps, that I should give my letter and Darwin’s answer in full. My letter ran thus:— _January_ 2, 1880. CHARLES DARWIN, ESQ., F.R.S., &c. DEAR SIR,—Will you kindly refer me to the edition of _Kosmos_ which contains the text of Dr. Krause’s article on Dr. Erasmus Darwin, as translated by Mr. W. S. Dallas? I have before me the last February number of _Kosmos_, which appears by your preface to be the one from which Mr. Dallas has translated, but his translation contains long and important passages which are not in the February number of _Kosmos_, while many passages in the original article are omitted in the translation. Among the passages introduced are the last six pages of the English article, which seem to condemn by anticipation the position I have taken as regards Dr. Erasmus Darwin in my book, “Evolution, Old and New,” and which I believe I was the first to take. The concluding, and therefore, perhaps, most prominent sentence of the translation you have given to the public stands thus:— “Erasmus Darwin’s system was in itself a most significant first step in the path of knowledge which his grandson has opened up for us, but to wish to revive it at the present day, as has actually been seriously attempted, shows a weakness of thought and a mental anachronism which no man can envy.” The _Kosmos_ which has been sent me from Germany contains no such passage.