To Albany Hancock 29 September 
Down Farnborough Kent
I am truly obliged to you for your very kind letter & offer of specimens of Alcippe.—1 You cannot imagine how much I shall enjoy seeing in your Paper & in actual specimens a new form of cirripede;2 for I am wearied out with examining scores & scores of closely allied common cirripedes.—
I shd. have written about Lithotrya in former letter, but I had hardly space, & I did not know whether you wd like to have my views, on this point.—3 I conclude that the L. forms its own holes from having seen numerous specimens, (& 4 or 5 species) large & small, all exactly fitting their cavities. The calcareous cup is indisputably (I speak after careful examination with dissolution in acids &c &c) formed by the cirripede & is common to most (I believe all) the species of genus. You are perfectly right that the calc. cup is never moved. But the cirripede inhabits (as far as I have seen) only cellular rocks, or corals, or shells (such as the cirripede Conia, with large tubes) & the pupa crawls into some minute cavity & there fixes itself for ever, & then as it grows enlarges the hole to required size; this it effects by the edges of the valves & of the minute scales on the peduncle, being sharply serrated; & as of course the serrated edge would soon be blunted, the calcareous scales on the peduncle are moulted with the membrane on which they are fixed, & new sharp ones periodically formed.— This (ie moulting of calc. scales) is a unique case, & I have no doubt is in relation to their boring necessities.—4 I believe this is the way which my Arthrobalanus which inhabits the Concholepas, also makes its cavities & its outer tissue is studded with elegant minute trifid & 4-fid points; & the shell is apparently first perforated by other animals;5 but I have got to go over this again with Arthrobalanus, but I have had the misfortune to lose nearly my whole stock of specimens, of which I collected thousands, for 15 years ago in the Chonos archipelago I described its peculiarities in some detail.—6
I venture to predict that if you take the outer tissue of Alcippe & clear the corium from it & place it under the compound microscope, you will find the rasping minute points, & I believe you state that it inhabits shells abounding with cavities of Cliona &c &c.—
I am most particularly obliged to you for informing me of Lovens cirripede,7 of which I had not heard.— I shd. be most grateful for a transcript of the paper & drawing—or if the book be not above 2 lb. or two precious cd. it not be sent & I would gratefully repay postage, & thus save Mr Alder8 the trouble of transcribing, to whom pray give my sincere thanks. I have in my collection this Cirripede as I suspect; it is like an Otion, & from not having calc. valves might be called an Alepas, but strange as it wd. appear to any one, who had not studied the internal structure of these animals, it is not even one of the Pedunculata, but belongs to the sessile division, & forms a new genus between Tubicinella & Coronula.—9 I shd. have been very sorry to have overlooked Loven’s description.—
I presume you have a superabundance of materials, but if at any time you wd like to have my small collection of naked mollusca, made during my circumnavigation, they are at your service; but I fear specimens preserved for many years in spirits, must be almost useless.— I think there are some new genera amongst them.—10
Once again allow me to thank you cordially for the very kind manner in which you have taken my request & believe me, dear Sir | Your’s sincerely obliged | C. Darwin To | A. Hancock Esqe
I see in the Athenæum they have omitted to express how valuable I thought your discovery & how interesting your whole paper.—11 I am very curious to see what you say about the palpi, I cd not follow the reading aloud, of this part, but if I understood right, the palpi are wonderfully different from anything I have ever seen in the Cirripedia.— I think it possible that Alcippe & Arthrobalanus may turn out distinct orders— The metamorphosis is certainly different— my larva has no thoracic legs, whereas yours has. mine is binocular, yours uniocular &c &c. Yet the 3 pair of cirri, the great lab〈rum〉 & habits are certainly strong points 〈o〉f resemblance.—12 I ought to apologise for the length of this letter.—
Thanks AH for specimens of Alcippe.
Discusses capacity of Lithotrya to bore its own hole. Believes Arthrobalanus also makes cavities this way.
Asks to see paper on cirripedes by Sven Lovén.
Comments on paper by AH [see 1253].