which the hens were spurred, and were found to disturb and break their eggs
much. With respect to the females of deer not having horns, I presume it
is to save the loss of organised matter. In your note you speak of sexual
selection and protection as sufficient to account for the colouring of all
animals, but it seems to me doubtful how far this will come into play with
some of the lower animals, such as sea anemones, some corals, etc., etc.
On the other hand Hackel (430/1. See "Descent of Man" (1901) page 402.)
has recently well shown that the transparency and absence of colour in the
lower oceanic animals, belonging to the most different classes, may be well
accounted for on the principle of protection.

Some time or other I should like much to know where your paper on the nests
of birds has appeared, and I shall be extremely anxious to read your paper
in the "Westminster Review." (430/2. "Westminster Review," July, 1867.)
Your paper on the sexual colouring of birds will, I have no doubt, be very
striking. Forgive me, if you can, for a touch of illiberality about your
paper.


LETTER 431. TO A.R. WALLACE.
March 19th, 1868.

(431/1. "The Variation of Animals and Plants" having been published on
January 30th, 1868, Mr. Darwin notes in his diary that on February 4th he
"Began on Man and Sexual Selection." He had already (in 1864 and 1867)
corresponded with Mr. Wallace on these questions--see for instance the
"Life and Letters," III., page 89; but, owing to various interruptions,
serious work on the subject did not begin until 1869. The following
quotations show the line of work undertaken early in 1868.