My dear Häckel,

I thank you for the present of your book, & I am heartily glad to see its great success.¹ You will do a wonderful amount of good in spreading the doctrine of Evolution, supporting it as you do, by so many original observations. I have read the new preface with very great interest. The delay in the appearance of the English translation vexes & surprizes me, for I have never been able to read it thoroughly in German, & I shall assuredly do so when it appears in English.² Has the problem of the later stages of reduction of useless structures ever perplexed you: this problem has of late caused me much perplexity. I have just written a letter to ‘Nature’ with a hypothetical explanation of this difficulty, & I will send you the paper with the passage marked.³ I will at the same time send a paper which has interested me; it need not be returned. It contains a singular statement bearing on so-called spontaneous generation.⁴ I much wish that this latter question could be settled; but I see no prospect of it. If it could be proved true this would be a most important to us. A good evolutionist in America, viz: E. Morse has lately published in the Proc. of the Boston Soc. Nat. Hist. a remarkable paper on the the Brachiopoda; & he seems to me to make out pretty clearly that they must be classed actually with Annelids.⁵ As for myself I have been working for many months on plants, viz:—on physiological points. Whenever I publish I will of course send you my little book.⁶

Wishing you every success in your admirable labours, I remain | My dear Häckel | Yours very sincerely | Charles Darwin