yours very faithfully,

ALFRED R. WALLACE.

Darwin had already written a short note to Wallace expressing a general
dissent from his views.

* * * * *

_4 Chester Place, Regent's Park, N.W. March 17, 1868._

My dear Wallace,--Many thanks about Pieridae. I have no photographs up
here, but will remember to send one from Down. Should you care to have a
large one, of treble or quadruple common size, I will with pleasure send
you one under glass cover, to any address you like in London, either now
or hereafter. I grieve to say we shall not be here on April 2nd, as we
return home on the 31st. In summer I hope that Mrs. Wallace and
yourself will pay us a visit at Down, soon after you return to London;
for I am sure you will allow me the freedom of an invalid.

My paper to-morrow at the Linnean Society is simply to prove, alas! that
primrose and cowslip are as good species as any in the world, and that
there is no trustworthy evidence of one producing the other. The only
interesting point is the frequency of the production of natural hybrids,
i.e. oxlips, and the existence of one kind of oxlip which constitutes a
third good and distinct species. I do not suppose that I shall be able
to attend the Linnean Society to-morrow.

I have been working hard in collecting facts on sexual selection every
morning in London, and have done a good deal; but the subject grows more
and more complex, and in many respects more difficult and doubtful. I
have had grand success this morning in tracing gradational steps by
which the peacock tail has been developed: I quite feel as if I had seen
a long line of its progenitors.

I do not feel that I shall grapple with the sterility argument till my
return home; I have tried once or twice and it has made my stomach feel
as if it had been placed in a vice. Your paper has driven three of my
children half-mad--one sat up to twelve o'clock over it. My second son,
the mathematician, thinks that you have omitted one almost inevitable
deduction which apparently would modify the result. He has written out
what he thinks, but I have not tried fully to understand him. I suppose
that you do not care enough about the subject to like to see what he has
written?

I hope your book progresses.

I am intensely anxious to see your paper in _Murray's Journal_.--My dear
Wallace, yours very sincerely,

CH. DARWIN.

* * * * *

_Hurstpierpoint.