My dear Friend

I am much obliged for your interesting letter with its genealogical tree.²

I now understand to a certain extent the importance of the swim-bladder in the Selachians.³ I shall be curious to see whether the organ ought not to be considered rather in a “nascent” than in a “rudimentary” state. I had always imagined that some animal like the Lepidosiren was the parent-form of the Vertebrata.—⁴

By all means keep the German edition of my Book: it will be of far more use in your hands than in anyone’s else.—⁵

We have been staying nearly a month in London & I am as wearied of the din & turmoil of the place, as you could be; but we return in two days to the quietude of Down.⁶ My visit here has not been one of rest, for I have been hard at work in collecting new facts on Sexual selection, by corresponding with a multitude of breeders & visiting them & the zoological Gardens.

This subject will be the chief one in my next little book, for I entirely agree with you that sexual selection has played a most important part with man.⁷ But I find many very serious objections & difficulties & shall not make out a very good case.—

I am astonished at the hybrids of Hare & rabbit: is it certain that D^r Conrad began his work with a true wild Lepus timidus & not with a hare-like var. of the L. cuniculus?⁸

I am tired with writing letters, so will write no more, & will conclude with my unalterable esteem & friendship.—

Yours very truly | Ch. Darwin