To P. B. Mason   31 March [1871]

My dear Sir

I am very much obliged for your prompt information.¹ In the next Edit. of my Book, I will certainly quote on your authority the statement about the hair on the back; it is quite new to me.—² No doubt the proportion of hairy backs out of even 100 children at the Hospital in Ormond St, would add immensely to the value of the statement; but I can hardly hope that you could persuade any medical man to take so much trouble.

Your suggestion is very good about the size of male infants, & my blindness equally bad.³ I suppose that I shall find in D^r. Duncan’s paper in Transact. of R. Soc^y. of Edinburgh, the actual weights of male & female infants; as I imagine he could not have overlooked this in giving the weights of infants from mothers of different ages.—⁴ Nevertheless I can hardly think that your solution, though it certainly ought not to be neglected, can apply to the whole case, as male infants for some years after birth die at a greater rate than female infants.

With cordial thanks | Pray believe me | Yours sincerely | Ch. Darwin