My dear Professor Donders,

I am greatly obliged to you for having taken such great trouble to illuminate one as ignorant as I am on the functions of the eye—¹ Your information has been many times of the greatest use to me; & what is even a still greater kindness, you have saved me from having fallen into many errors—²

I have received the German Pamphlet & read the part indicated; & have written to Bowman to borrow M^r Wells’ work.³ When I go again over my M.S., I will carefully reconsider all that I have written; & as the subject is so intricate, the result I think will be that I will strike out a good deal, & only give some facts & quote what you have told me—⁴

I feel every day that to write on expression, a man ought to have ten times as much physiological knowledge as I possess; but I hope to succeed in giving a good many observations, especially on the expression and gestures of Savages; & then some one hereafter will correct my speculations.

I must again say how extremely kind it is in you, full of knowledge & busily employed as you are to spend so much time in aiding me.

Believe me | Yours very gratefully— | Charles Darwin.