From W. S. Dallas 11 December 1867
Yorkshire Philosophical Society | York
11th. Decr. 1867
My dear Sir
I write to apologise to you if the remarks in my note of Sunday last seem to you so much in the nature of criticism as I fear they do.—1 Nothing was further from my intention.— The questions as to the use of the name Tadorna, the name of the Pheasant & the transposition of the notes were necessary ones,— the use of Dragon instead of Dragoon is of not the least consequence, but as I was more familiar with the latter name I noted it in passing,—& the Arab matter I mentioned, not as pointing out an error, but because I thought you might feel interested in the explanation of the point.—2
I last night timed myself & found that in 5 hours hard work I got through 3 sheets less 2 pages, & this is more than I have been able to do sometimes since working the whole of the references together.—3 The subjects often seem to elude the Index-maker, as the noticing every point taken up would often be to transpose whole pages in an altered form to the Index,—& on the other hand it is difficult, or sometimes impossible to hit upon any middle course between this elaborate Analysis & the simple notice of the general subject.—
Of course this note requires no answer, but you may depend on my pushing forward at my best speed.—
Believe me | Your’s very truly | W. S. Dallas
C. Darwin Esqr.
Regrets that the remarks in his letter  seemed to CD to be criticisms. Nothing was further from his intention. He is working hard. "The subjects often seem to elude the Index-maker."