TO J.JENNER WEIR.
(309/1.

On December 27th, 1881, Mr.Jenner Weir wrote to Mr.Darwin: "After some hesitation in lieu of a Christmas card, I venture to give you the return of some observations on mules made in Spain during the last two years...It is a fact that the sire has the prepotency in the offspring, as has been observed by most writers on that subject, including yourself.

The mule is more ass-like, and the hinny more horse-like, both in the respective lengths of the ears and the shape of the tail; but one point I have observed which I do not remember to have met with, and that is that the coat of the mule resembles that of its dam the mare, and that of the hinny its dam the ass, so that in this respect the prepotency of the sexes is reversed." The hermaphroditism in lepidoptera, referred to below, is said by Mr.Weir to occur notably in the case of the hybrids of Smerinthus populi-ocellatus.) Down, December 29th, 1881.
I thank you for your "Christmas card," and heartily return your good wishes.

What you say about the coats of mules is new to me, as is the statement about hermaphroditism in hybrid moths.

This latter fact seems to me particularly curious; and to make a very wild hypothesis, I should be inclined to account for it by reversion to the primordial condition of the two sexes being united, for I think it certain that hybridism does lead to reversion.
I keep fairly well, but have not much strength, and feel very old.
LETTER 310.