Dear Sir

Although I have not the pleasure of your personal acquaintance, I hope & think that you will excuse the liberty which I take in writing to you. I have lately read some papers formerly published by you in the Ibis, in which you specify various birds coloured so as to resemble the desert.¹ Now I sh^d be greatly obliged if you would inform me whether with these birds the two sexes closely resemble each other, & whether, as far as known, the young resemble the adults. As I did not think that this subject w^d specially concern me, I unfortunately returned the vols without making an extract   Therefore I sh^d be much obliged if you w^d give me a reference. I read, about a year ago, with lively interest your work on the Sahara, & if I am not mistaken there was in it a similar discussion on the colouring of desert-birds.² If it w^d not cause you too much trouble, I sh^d very much like to be permitted to quote from you some such sentence as follows “M^r Tristram informs me that about … birds, inhabitants of the Sahara, are coloured in a protective manner so as to resemble the surrounding desert.³ In all these species (or in $\frac{2}{3}$ or $\frac{1}{2}$ &c (?)) the 2 sexes in the adult state, & the young resemble each other; yet about $\frac{1}{2}$, $\frac{1}{3}$, or $\frac{1}{4}$ (?) of these birds belong to groups in which the sexes usually differ to a certain extent in colour”.

I hope that you will excuse me troubling you & if in your power grant me this favour.

Pray believe me dear Sir | yours faithfully | Charles Darwin