I should much like to know whether nestlings do really thus erect their feathers. I am now at work on expression in animals of all kinds, and birds; and if you have any hints I should be very glad for them, and you have a rich wealth of facts of all kinds. Any cases like the following: the sheldrake pats or dances on the tidal sands to make the sea-worms come out; and when Mr. St. John's tame sheldrakes came to ask for their dinners they used to pat the ground, and this I should call an expression of hunger and impatience. How about the Quagga case? (469/2. See Letter 235, Volume I.)

I am working away as hard as I can on my book; but good heavens, how slow my progress is.

LETTER 470. TO F.C. DONDERS. Down, March 18th, 1871.

Very many thanks for your kind letter. I have been interested by what you tell me about your views published in 1848, and I wish I could read your essay. It is clear to me that you were as near as possible in preceding me on the subject of Natural Selection.

You will find very little that is new to you in my last book; whatever merit it may possess consists in the grouping of the facts and in deductions from them. I am now at work on my essay on Expression. My last book fatigued me much, and I have had much correspondence, otherwise I should have written to you long ago, as I often intended to tell you in how high a degree your essay published in Beale's Archives interested me. (470/1. Beale's "Archives of Medicine," Volume V., 1870.) I have heard others express their admiration at the complete manner in which you have treated the subject. Your confirmation of Sir C. Bell's rather loose statement has been of paramount importance for my work. (470/2. On the contraction of the muscles surrounding the eye. See "Expression of the Emotions," page 158. See Letters 464, 465.) You told me that I might make further enquiries from you.

When a person is lost in meditation his eyes often appear as if fixed on a distant object (470/3. The appearance is due to divergence of the lines of vision produced by muscular relaxation. See "Expression of the Emotions," Edition II., page 239.), and the lower eyelids may be seen to contract and become wrinkled. I suppose the idea is quite fanciful, but as you say that the eyeball advances in adaptation for vision for close objects, would the eyeball have to be pushed backwards in adaptation for distant objects? (470/4. Darwin seems to have misunderstood a remark of Donders.) If so, can the wrinkling of the lower eyelids, which has often perplexed me, act in pushing back the eyeball?

But, as I have said, I daresay this is quite fanciful. Gratiolet says that the pupil contracts in rage, and dilates enormously in terror. (470/5. See "Expression of the Emotions," Edition II., page 321.) I have not found this great anatomist quite trustworthy on such points, and am making enquiries on this subject. But I am inclined to believe him, as the old Scotch anatomist Munro says, that the iris of parrots contracts and dilates under passions, independently of the amount of light. Can you give any explanation of this statement? When the heart beats hard and quick, and the head becomes somewhat congested with blood in any illness, does the pupil contract? Does the pupil dilate in incipient faintness, or in utter prostration, as when after a severe race a man is pallid, bathed in perspiration, with all his muscles quivering? Or in extreme prostration from any illness?

LETTER 471. TO W. TURNER. Down, March 28th [1871].

I am much obliged for your kind note, and especially for your offer of sending me some time corrections, for which I shall be truly grateful. I know that there are many blunders to which I am very liable. There is a terrible one confusing the supra-condyloid foramen with another one. (471/1. In the first edition of the "Descent of Man," I., page 28, in quoting Mr. Busk "On the Caves of Gibraltar," Mr. Darwin confuses together the inter-condyloid foramen in the humerus with the supra-condyloid foramen.

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