Dear Sir

I venture to ask you the following questions:— I occasionally find the so-called opponents of Evolution point to the Trilobite, which existed from the Silurian to the Mountain Limestone without change as a fact subversive of Evolution. But is not this a case of “persistence” under favourable conditions, and as such an additional proof of the truth of Evolution?¹ And, as the ocean is and has been less liable to be affected by climatal changes than the land, might not such instances be expected to occur more frequently in the former than upon the latter?

I have seen it stated by a writer whom I believed to be an authority, but whose name I cannot remember, that there are minute organisms which are animal at one period of their existence and vegetable at another. As I am unable to authenticate this statement, and think it doubtful, will you kindly say whether it is, or is not true? I know that it is impossible to name as distinctly animal or distinctly vegetable many of the lower organisms.— hence Prof. Haeckel’s division of the Protista.²

I am fully aware of the value of your time, and should you think my questions trivial, pray set this note aside. I cannot, however, conclude without thanking you for the noble work you have performed in the cause of science, and, with the highest respect, subscribe myself,

Yours sincerely | W^m. Horsfall

D^r. Chas. Darwin F.R.S. &c: &c:.