To G. G. Stokes   28 February [1868]¹

My dear Sir

I am very much obliged to you for your great kindness in writing to me at such length about the colours of the peacock’s feathers.² As you say that you will look at it again, will you have the kindness to attend to one point, namely, whether a gradual thickening or thinning by little steps from the centre to the circumference, of the film of colouring matter w^d account for the zones of colour which occur; or must there be zones of different kinds of colouring matter?

With very sincere thanks | believe me my dear Sir | yours truly | Charles Darwin