My dear Sir

I am very much obliged for your last very interesting letter, with your answers to all my queries, & the copy of your Paper, which I am very glad of, though I take in the Annals.—¹

I have not yet looked at Alcippe for I have found my writing work run out, & I have lately received several new pedunculate species to describe.— I have had such a misfortune in the loss of a parcel of cirripedes from Copenhagen, amongst which was the curious Alepas squalicola! the knowledge of which I owe to M^r Alder’s kindness.— I have of course read your description of Alcippe, & it is most clear & definite: I hope to put Arthrobalanus in same order with it,² but it will be stretching a point to do so, & they must form distinct families, more distinct than any Pedunculate & any Sessile cirripede are from each other.— I hope before long to indulge in a look at Alcippe.

I have had occasion to re-look over many specimens of Lithotrya,³ & am as fully convinced as ever that the basal cup is fixed at very early period, & is never moved.— In one specimen several specimens were embedded in rock parallel but in reversed positions (& others at right angles) & of the parallel ones the greater number had their capitulums (ie shell & or valves) directed from the exterior surface of the rock inwards, so that they c^d never reach the surface, & must have lived in subterranean cavity: I am as much as ever in dark, whether the larva creeps in, or bores in.—

I had intended, but forgot, to ask you about the Clitia,; all which I have seen (except some rare foreign species which I have not yet touched) were fixed on fuci & stones; &, if it be not asking too great a favour, I sh^d be very much obliged, if you would permit me to look at any fixed on shell. Several months ago I had one rather careful inspection of the basal membrane & was much surprised not to be able to see the prehensile antennæ of the pupa, or any orifices for the cement-stuff; yet from analogy I can hardly doubt that Clitia fixes itself like all other Cirripedes, in the manner briefly explained by me to Brit. Assoc.—⁴

In case of Coronula, Tubicinella & Chelonobia I have fancied, that the sinking was entirely or chiefly owing to growth of surrounding parts of the animal to which the cirripedes were attached. I am much surprised about Clitia, it shows me that there is even in common cirripedes something about their attachment which I do not understand at all.— I have seen, as I believe, that the cement could corrode through membrane of its own peduncle but not act on the calcareous scales supported by this membrane; so that your fact of the Modiola is still odder, & I hope that you will allow me to quote it from you.—⁵

I have seen the larvæ of most of the species of Anatifa, & I think of A. vitrea,⁶ but I have had either to dissect them out of egg & just after their escape, & never as yet when naturally sent forth from parent. In the state, in which I have seen them, they certainly had not any “process or pedicel”; but exactly at the spot figured by you, lies their mouth, which is very slightly prominent, without any trophi, & leading into an œsophagus running anteriorly & lost in cellular matter.⁷

If you c^d let me have a few of these specimens I sh^d be very much obliged; & especially if you w^d give me any precise observations of your own on this “pedicel”, for I do not in the least doubt that, with all your experience in dissecting, your observations w^d be more trustworthy than my own.— Goodsir figures something like a masticating organ attached to base of legs of larvæ,⁸ which I c^d never see, & which if such exist, w^d be a strange coincidence with Limulus.— No doubt you are aware that in all Cirripedes the larva from the stage which you have figured, becomes (so called) bivalve, hexapod, with prehensile antennæ binocular &c.; & when it attaches itself it is in fact a natatory pupa for it has no mouth only a rudimentary shrivelled œsophagus, surrounded by the forming trophi of the young cirripede.— Arthrobalanus alone passes the 1^st larva stage in egg, & appears when first born with prehensile antennae & two eyes. &c.—

But perhaps I weary you with these details; one forgets that others do not care so much for a subject, as he who is at work on it.—

I have not yet gone through my bottles for Mollusca, but will you be so good as to send me one line, to say whether you care for any naked terrestrial (as Vaginulus, Parmacella) or aquatic naked mollusca, or for any of Cuvier’s “Tectibranches” as Aplysia &c.—or whether exclusively for the Nudibranch.; I believe I have a few of each order.—

I fear you will think that I have written to you at unreasonable length.— Pray believe me, | My dear Sir | Your’s very sincerely | C. Darwin

I begin to think I shall spend my whole life on Cirripedia, so slow is my progress working only 2 to 3 hours daily.—