I have come here for a few weeks, for a little change and rest. Just as I
was leaving home I received your first note, and yesterday a second; and
both are most interesting and valuable to me. That is a very curious
observation about the goldfinch's beak (435/1. "Descent of Man," Edition
I., Volume I., page 39. Mr. Weir is quoted as saying that the birdcatchers
can distinguish the males of the goldfinch, Carduelis elegans, by their
"slightly longer beaks."), but one would hardly like to trust it without
measurement or comparison of the beaks of several male and female birds;
for I do not understand that you yourself assert that the beak of the male
is sensibly longer than that of the female. If you come across any acute
birdcatchers (I do not mean to ask you to go after them), I wish you would
ask what is their impression on the relative numbers of the sexes of any
birds which they habitually catch, and whether some years males are more
numerous and some years females. I see that I must trust to analogy (an
unsafe support) for sexual selection in regard to colour in butterflies.
You speak of the brimstone butterfly and genus Edusa (435/2. Colias
Edusa.) (I forget what this is, and have no books here, unless it is
Colias) not opening their wings. In one of my notes to Mr. Stainton I
asked him (but he could or did not answer) whether butterflies such as the
Fritillaries, with wings bright beneath and above, opened and shut their
wings more than Vanessae, most of which, I think, are obscure on the under
surface. That is a most curious observation about the red underwing moth
and the robin (435/3. "Descent of Man," Edition I., Volume I., page 395.
Mr. Weir describes the pursuit of a red-underwing, Triphoena pronuba, by a
robin which was attracted by the bright colour of the moth, and constantly
missed the insect by breaking pieces off the wing instead of seizing the
body. Mr. Wallace's facts are given on the same page.), and strongly
supports a suggestion (which I thought hardly credible) of A.R. Wallace,
viz. that the immense wings of some exotic lepidoptera served as a