My dear M^r. Agassiz

I cannot thank you enough for your letter of Aug 9^th, which, even if I had not wished much to learn something about the pedicillariæ, would at any time have interested me beyond measure.² It is a splendid case of gradation of structure. I wish extremely I could give the whole of the case, but this is impossible from want of space, even if I had the requisite knowledge to do it well; but I must give some of your conclusions & remarks.³ Over & over again I have come across some structure, & thought that here was an instance in which I sh^d. utterly fail to find any intermediate or graduated structure; but almost always by keeping a look out I have found more or less plain traces of the lines through which development has proceeded by short & easy & serviceable steps. Rarely, however, have I learnt so fine an instance as this of yours.— I have been very unwell for the last 5 weeks with giddiness & horrid head feelings & have done nothing: I was not able to read your letter at one time, but now I have just finished it, & it has served as a more splendid stimulus than any physic, & has enabled me to write myself this note.

Accept my cordial thanks, & believe me | yours very sincerely | Ch. Darwin

I am very much obliged for the beautiful book, “Sea-side Studies”, which I will read as soon as my odious head allows me to read anything.⁴