Darwin did use tuning forks for experiments with spiders.
Inset: Charles Darwin, photo probably by Messrs. Maull and Fox, around 1854, see also commons.wikimedia.org/wiki/File:Charles_Darwin_aged_51.jpg.
Inset in inset: Charles Darwin's "I think" sketch of the
evolutionary tree (about July 1837, 1st notebook 1837-1838, page 36) compared to a "weed" in
the lower left corner of Holiday's illustration. I learned, that
Darwin did not keep his notebook secret after the publication of On the Origin of Species, but I do not know of any presentation of his sketch before 1876.
Thus, the resemblance between the "weed" and Darwin's
evolutionary tree sketch may be purely incidental.
(1) This is a new version of www.flickr.com/photos/bonnetmaker/4481587379/
(2) commons.wikimedia.org/wiki/File:CharlesDarwinHuntingSnark.jpg, License as in Flickr: CC-BY-SA-3.0
(3) The person on the right side in Holiday's illustration is "The Banker". This figure has different faces in different illustrations.
(4) Henry Holiday may have been inspired by Darwin's "tree of life" sketch when he did his illustrations to Lewis Carroll's The Hunting of the Snark. However, the problem with my guess is, that (as far as I know) in and before 1876 the sketch still may not have been known to the public.