Dear & esteemed Sir

Your letter has given me great pleasure, for permit me to say that I have long honoured your name as that of one of the best naturalists in Europe. I am very much obliged for your two Memoirs, which I am sure will interest me, but I am a poor German scholar & I have another book which I must finish reading first.¹

I earnestly hope that you will publish your lecture, as the judgment of so experienced a naturalist must be of value to every one; & for myself I much wish to read your criticisms & facts. Of course I think very highly of Häckel’s abilities & his works; I should indeed be very insensible to praise if I did not do so; but I dare say he is too enthusiastic & too bold in drawing conclusions.² I have been particularly glad to hear what you say about M. Wagner’s interesting pamphlet. Perhaps I have underrated the importance of isolation, but I am now correcting a new edit. of my “Origin of species”, & I do not find that I have much or any thing to alter on this head.³

I cannot tell you how glad I am to hear that you intend to study the metamorphoses of the Lepads.⁴ As you are a much better dissector than I am, & have so much knowledge of the lower Crustaceans, I have no doubt that you will find much that I have overlooked or misunderstood.

I still cannot avoid believing that the lateral horns of the larvæ in the first stage include the antennæ of the second stage.⁵ I wish you could be induced to examine the curious organ which I suppose I falsely called the acoustic sack.⁶ But beyond every thing I hope that you will be able to examine the Complementary males of Scalpellum, which no one else has ever seen.⁷ I shall never forget my astonishment when I first made out their nature. I sh^d think you w^d be able to find some where specimens in spirits. I grieve to say I can give you very little help. When I finished my work I returned almost all the specimens to their owners. The few which I kept have been entirely forgotten, & now I find to my great disappointment that some which w^d have been useful to you are quite dried up. I have however the following specimens not quite spoilt.

(1) Xenobalanus, that curious form resembling Lepas but really allied to Coronula—in pretty good state⁸

(2) A single small Scalpellum; & I am nearly sure that with only a hand-lens, I see a complementary male on each side, but I do not like to cut off the valve to examine carefully.

(3) The shell of Concholepas, after being treated with acid, & which formerly abounded with Cryptophialus but whether they are in a good state I will not say.⁹

(4) Some fragments of shell with Alcippe,¹⁰ but again I do not know in what state.—

Lastly 17 slides with various fragments & minute specimens; I can see one male Alcippe in a pretty good state, & some larvæ of the first stage of Scalpellum; these larvæ are of remarkable size.—

Now w^d these specimens be worth your acceptance? They need not be returned, & I can send a list of the slides, which however are in a poor condition. If you think these specimens worth sending you must tell me the best means of sending them. They will all go in a very small box, but much too heavy for the post.

Lastly you must let me have the pleasure of sending you in 2 or 3 months time the New edit. of the Origin some parts of which I hope I have improved.¹¹

With the most sincere esteem & respect, I remain Dear Sir Yours very faithfully | Ch. Darwin

P.S. Would you have the great kindness to send me your Photograph, as I have a collection of the best naturalists.—