P.S.—­I have now finished the review:  there can be no doubt it is by Mivart, and wonderfully clever.

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Holly House, Barking, E. July 16, 1871.

Dear Darwin,—­I am very sorry you are so unwell, and that you allow criticisms to worry you so.  Remember the noble army of converts you have made! and the host of the most talented men living who support you wholly.  What do you think of putting C. Wright’s article as an appendix to the new edition of the “Origin”?  That would get it read, and obviate my chief objection, that the people who read Mivart and the “Origin” will very few of them buy a separate pamphlet to read.  Pamphlets are such nuisances.  I don’t think Mivart could have written the Quarterly article, but I will look at it and shall, I think, be able to tell.  Pray keep your spirits up.  I am so distracted by building troubles that I can write nothing, and I shall not, till I get settled in my new house, some time next spring, I hope.—­With best wishes, believe me yours very faithfully,

ALFRED R. WALLACE.

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Haredene, Albury, Guildford.  August 1, 1871.

My dear Wallace,—­Your kind and sympathetic letter pleased me greatly and did me good, but as you are so busy I did not answer it.  I write now because I have just received a very remarkable letter from Fritz Mueller (with butterflies’ wings gummed on paper as illustrations) on mimicry, etc.  I think it is well worth your reading, but I will not send it, unless I receive a 1/2d. card to this effect.  He puts the difficulty of first start in imitation excellently, and gives wonderful proof of closeness of the imitation.  He hints a curious addition to the theory in relation to sexual selection, which you will think madly hypothetical:  it occurred to me in a very different class of cases, but I was afraid to publish it.  It would aid the theory of imitative protection, when the colours are bright.  He seems much pleased with your caterpillar theory.  I wish the letter could be published, but without coloured illustrations [it] would, I fear, be unintelligible.

I have not yet made up my mind about Wright’s review; I shall stop till I hear from him.  Your suggestion would make the “Origin,” already too large, still more bulky.

By the way, did Mr. Youmans, of the United States, apply to you to write a popular sketch of Natural Selection?  I told him you would do it immeasurably better than anyone in the world.  My head keeps very rocky and wretched, but I am better,—­Ever yours most truly,

C. DARWIN.

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Holly House, Barking, E. March 3, 1872.