Ɛpsilon

To Francisco de Arruda Furtado   31 October 1881

Down, | Beckenham, Kent. | (Railway Station | Orpington. S.E.R.)

Oct 31. 1881

Dear Sir

I am extremely glad that you think that you will find Wallace’s work useful.1

The egg-cases of Blatta, (as I suppose, for I am ignorant on the subject) with their white coating are curious. I scraped off some of the white matter & placed it in Acetic Acid. It effervesced, leaving a fine residue. I suppose, therefore, that it is some kind of cement or plaister. Are you sure that the place bearing the egg-case had not been white-washed, with cement or white-wash, after the egg-cases had been affixed by the insect?2

If you can observe again similar cases, I think that the fact would be worth publishing, as a good instance of skill in protection.— I can remember no such case. I have, as usual, many letters to write, so will say no more; except to wish you continued success—

Dear Sir | Yours faithfully | Ch. Darwin

1
See letter from Francisco de Arruda Furtado, 16 October 1881 and n. 2. CD had sent a copy of Alfred Russel Wallace’s Geographical distribution (Wallace 1876).
2
See letter from Francisco de Arruda Furtado, 22 October 1881 and n. 3. Blatta is a genus of cockroaches. Arruda Furtado had written that the chalk covering the egg casing had been chewed and applied on the sides not attached to the wall. Chalk or lime containing calcium carbonate (CaCO3) reacts with acetic acid (CH3CO2H) to form carbonic acid (H2CO3) and calcium acetate (Ca(C2H3O2)2). The carbonic acid breaks down to water and carbon dioxide, which causes the effervescing.

Manuscript Alterations and Comments

0.1 (Railway … S.E.R.)] parentheses added
2.3 residue.] point over comma
2.4 bearing … case] interl
3.1 again] interl
3.1 the fact] ‘the’ altered from ‘they’

Please cite as “DCP-LETT-13444,” in Ɛpsilon: The Charles Darwin Collection accessed on 5 June 2025, https://epsilon.ac.uk/view/dcp-data/letters/DCP-LETT-13444