the region inhabited by the generic or family type in question. The
manufactory of new species has ceased, or nearly so, and in that case I
suppose a variety is more likely to be one of the transitional links
which has not yet been extinguished than the first step towards a new
permanent race or allied species....

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.

* * * * *

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.

* * * * *

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 t