My dear Huxley.

I really am much obliged to you for looking at my preparations; I feel it quite a comfort that some one sh^d. have seen what once filled me with astonishment.—¹ You c^d. not do better than take Conchoderma aurita for the cement-glands, (if you ever have time to look for yourself) for everything here is in its very simplest stage: & here you will be able with care to see what I consider the strangest part of the whole structure of cirripedes the metamorphosis or adaptation of part of the branching ovaria to the cement-organs, about the truth of which, strange as it may be, I cannot doubt.—² In my volume on the Lepadidæ p. 57 & 58, you will see why I consider the salivary glands of Cuvier to be the true ovaria.³ It was difficult to doubt the meaning of the passage of the little pellets of cells with nuclei from the glands down the two unbranched ovarian tubes into the mass at the base of shell or into the peduncle. The ova are never developed in these glands. Conchoderma aurita is eminently good for tracing development of ova, (before impregnation) from the tubes round the base, of the sack, (within the capitulum) lie in a single plane.

I felt to a degree you will hardly appreciate, the want of knowledge of minute or microscopical structure: if I had to begin again, I w^d. devote 6 months to understand cells, nuclei, germinal vesicles &c &c. My idea, (I know not how unlikely) is that the germinal vesicles alone are formed in the true ovaria (by the mouth) & that the whole rest of development before impregnation goes on at basis or within peduncle, & impregnation takes place within the sack, after the exuviation, by which the eggs may be said to be laid.—

Lastly the main reason which caused me to separate the Cirripedes so completely as I have from ordinary Crustaceans, is, my firm belief, that the resemblance of the larvæ to Entomostraca is only analogical & that the natatory organs are not at all similar in the two,—that the law of development is very different.⁴ I give this conclusion briefly at p. 16 of the Balanidæ, & my reasons at tedious length at p. 102.—

How difficult a subject is the classification of the higher groups in any class: see how Dana & Milne Edwards, such competent judges, differ!⁵ Dana approves of my classification, but will not, from analogy alone, admit my views of the homologies of the limbs.—

Should you ever go on with subject, do read my account of Proteolepas: it strikes me as a truly extraordinary animal.—⁶

I promise I will never bore you again on Cirripedes.—

I must just say, that you are quite right to doubt me in every way, for what blunders are made. I stopped being sent to Royal Soc^y. an elaborate paper, in which a quite independent parasite was minutely described, as the ovarium of a Balanus, & all the stages of development of the eggs of the parasite were minutely described as those of Cirripedes!—⁷

Many thanks for your paper out of the Encyclop: on Mollusca,⁸ of which I had heard from two quarters. I have read it with attention & interest, for I had often wondered how a gasteropod, a bivalve, & cephalopod c^d. be brought to same type. It appears to me satisfactory, but it w^d. be hypocritical in me to let you suppose my opinion of any value, for really I do not know enough of the essential points of structure to form an independent opinion.—

An acephalous Mollusc has always looked to me a complete mystery, & I really know no more about it, than a man does, who has only eat oyster patties; the relation of the animal to the shell & crust being about the same in my eyes.— There was no reason for your writing down to ignoramuses, & indeed without beautiful figures, I sh^d. think you could not; but if you ever lectured on the subject, I think you ought to take more pains in making your hearers realise the structure of the acephalous mollusca, & heteropods, & indeed cephalopods, & how a common land-snail corresponds with a whelk.— I can, however, so far judge that to anyone commencing to examine for himself the several great classes of Mollusca, your paper would be quite invaluable.—

Pray believe me | Your’s very sincerely | C. Darwin