Your last letter will be of great use to me.  I had cited the case of beetles recovering from immersion of hours in alcohol from my own experience, but am glad it strikes you in the same light.  McAndrew told me last night that the littoral shells of the Azores being European, or rather African, is in favour of a former continental extension, but I suspect that the floating of seaweed containing their eggs may dispense with the hypothesis of the submersion of 1,200 miles of land once intervening.  I want naturalists carefully to examine floating seaweed and pumice met with at sea.  Tell your correspondents to look out.  There should be a microscopic examination of both these means of transport.—­Believe me ever truly yours,

CHA.  LYELL.

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SIR C. LYELL TO A.R.  WALLACE

73 Harley Street.  July 3, 1867.

My dear Mr. Wallace,—­I was very glad, though I take in the Westminster Review, to have a duplicate of your most entertaining and instructive essay on Mimicry of Colours, etc., which I have been reading with great delight, and I may say that both copies are in full use here.  I think it is admirably written and most persuasive.—­Believe me ever most truly yours,

CHA.  LYELL.

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TO HERBERT SPENCER

Hurstpierpoint, Sussex.  October 26, 1867.

My dear Mr. Spencer,—­After leaving you yesterday I thought a little over your objections to the Duke of Argyll’s theory of flight on the ground that it does not apply to insects, and it seems to me that exactly the same general principles do apply to insects as to birds.  I read over the Duke’s book without paying special attention to that part of it, but as far as I remember, the case of insects offers no difficulty in the way of applying his principles.  If any wing were a rigid plane surface, it appears to me that there are only two ways in which it could be made to produce flight.  Firstly, on the principle that the resistance in a fluid, and I believe also in air, increases in a greater ratio than the velocity (? as the square), the descending stroke might be more rapid than the ascending one, and the resultant would be an upward or forward motion.  Secondly, some kind of furling or feathering by a rotatory motion of the wing might take place on raising the wings.  I think, however, it is clear that neither of these actions occurs during the flight of insects.  In both slow- and quick-flying species there is no appearance of such a difference of velocity, and I am not aware that anyone has attempted to prove that it occurs; and the fact that in so many insects the edges of the fore and hind wings are connected together, while their insertions at the base are at some distance apart, entirely precludes a rotation