My dear Darwin,—­Yours just received was very welcome, and the delay in its reaching me is of no importance whatever, as, having seen the announcement of the Queen’s approval of the pension, of course I felt it was safe.  The antedating of the first payment is a very liberal and thoughtful act; but I do not think it is any way exceptional as regards myself.  I am informed it is the custom because, as no payment is made after the death of the person, if the first payment were delayed the proposed recipient might die before the half-year (or quarter-day) and thus receive nothing at all.

I suppose you sent the right address to Mr. Seymour.  I have not yet heard from him, but I daresay I shall during the next week.

As I am assured both by Miss Buckley and by Prof.  Huxley that it is to you that I owe in the first place this great kindness, and that you have also taken an immense amount of trouble to bring it to so successful issue, I must again return you my best thanks, and assure you that there is no one living to whose kindness in such a matter I could feel myself indebted with so much pleasure and satisfaction.—­Believe me, dear Darwin, yours very faithfully,

ALFRED R. WALLACE.

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Down, Beckenham, Kent.  July 9.

My dear Wallace,—­Dr. G. Krefft has sent me the enclosed from Sydney.  A nurseryman saw a caterpillar feeding on a plant and covered the whole up, but, when he searched for the cocoon [pupa], was long before he could find it, so good was its imitation, in colour and form, of the leaf to which it was attached.

I hope that the world goes well with you.  Do not trouble yourself by acknowledging this.—­Ever yours,

CH.  DARWIN.

Accompanying this letter, which has been published in “Darwin and Modern Science” (1909), was a photograph of the chrysalis (Papilio sarpedon choredon) attached to a leaf of its food-plant.  Many butterfly pupae are known to have the power of individual adjustment to the colours of the particular food-plant or other normal environment; and it is probable that the Australian Papilio referred to by Darwin possesses this power.

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Nutwood Cottage, Frith Hill, Godalming, July 9, 1881.

My dear Darwin,—­I am just doing, what I have rarely if ever done before—­reading a book through a second time immediately after the first perusal.  I do not think I have ever been so attracted by a book, with perhaps the exception of your “Origin of Species” and Spencer’s “First Principles” and “Social Statics.”  I wish therefore to call your attention to it, in case you care about books on social and political subjects, but here there is also an elaborate discussion of Malthus’s “Principles of Population,” to which both you and I have acknowledged ourselves indebted.  The present writer, Mr. George, while