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Darwin Correspondence Project

To J. F. W. Herschel   11 May [1848]

Down Farnborough Kent

May 11

Dear Sir John Herschel

Knowing that you are interested about Colours, I venture to mention the following fact, which if, as is most probable, you do not care about, please to take no notice of this note, which otherwise I should not think of troubling you with.

The genus Ibla is a Cirripede or Barnacle, of which the valves of operculum consist of a horny substance, instead of being as in all other genera calcified. This horny substance is hard, & translucent, & consists I believe of Chitine or Entomoline. The borders of the valves when a slice is scaled off are of a very fine blue colour, but which colour, (& this is the point) on slight pressure instantly changes into a translucent red like the clouds of sunset.1 It is curious under the microscope to press it with a needle & see spot after spot assume this fine permanent glow of red. Acetic & Muriatic acids produce the same effect without pressure. Caustic potash has no action on it. I could, if by chance you feel any interest in this point, send you a valve. The Ibla is a quite small animal from the Phillippines. Cirripedes are nothing but Crustaceans fixed to a support.

Pray believe me, | Yours sincerely | C. Darwin To | Sir J. W. Herschel Bart.

Footnotes

The genus Ibla is described in Living Cirripedia (1851): 180–214. CD reported the colour change of the valves on p. 184. See letter to J. F. W. Herschel, 6 June [1848].

Summary

Describes colour changes from blue to red in valves of operculum of the cirripede genus Ibla.

Letter details

Letter no.
DCP-LETT-1175
From
Darwin, C. R.
To
Herschel, J. F. W.
Sent from
Down
Source of text
The Royal Society (HS6: 12)
Physical description
3pp

Please cite as

Darwin Correspondence Project, “Letter no. 1175,” accessed on 9 December 2016, http://www.darwinproject.ac.uk/DCP-LETT-1175

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