Dear Sir

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 sh^d. have written about Lithotrya in former letter, but I had hardly space, & I did not know whether you w^d 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 sh^d. be most grateful for a transcript of the paper & drawing—or if the book be not above 2 lb. or two precious c^d. it not be sent & I would gratefully repay postage, & thus save M^r 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 w^d. 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 sh^d. have been very sorry to have overlooked Loven’s description.—

I presume you have a superabundance of materials, but if at any time you w^d 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 Esq^e

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 c^d 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.—