I am very much obliged to Mr Bennett for his information about Norwegian dun ponies;² but I received some years ago, through the Consul-General, Mr Crowe, the same account, which probably came from Mr Bennett.³ The point on which I am anxious for information is, whether a cross between two coloured horses (neither of which are dun) ever produce duns. I believe that we could thus obtain some insight into the aboriginal colour of the horse. I have as yet only a single case of the parentage of a dun—namely, a bay horse and black mare. A German writer (Hofacker) on the breeding of horses gives the case of two chesnuts producing a “goldfalb”, which, I believe, is a dun; and of a chesnut and brown producing a mouse-dun (mausrapp).⁴ I hope “Eques” will fulfil his kind offer of giving more information on the subject.⁵ I have collected a considerable body of evidence on the remarkable tendency of the offspring of a cross between differently-coloured breeds reverting to the colour of the aboriginal parent.⁶ With pigeons, I made numerous crosses for this express purpose, and frequently got a near approach to the marks and colour of the wild rock-pigeon.⁷ Again, I crossed a Spanish cock and white silk-hen; and one of the cockerels, although at first coal-black, in the autumn assumed the splendid red plumage of the wild jungle-cock (Gallus bankiva). Two young Cocks from the black Spanish and white game-hen assumed red neck and saddle hackles, so as partly to resemble a pile game cock. Mr Brent crossed two varieties of duck, and some of the ducklings assumed the plumage of the wild duck.⁸ I could give other facts. For instance, it is asserted in work on poultry that hens raised from a cross between two breeds of fowls neither of which sit, are good sitters; and here we see a cross has brought back the proper aboriginal instinct of incubation. In my own experience, however, the crossed offspring from the Spanish cock and a Poland hen did not incubate. If anyone has any analogous facts to those above given, and would communicate them, I should be much obliged. The whole subject of the results of crossing distinct breeds is an interesting one under many points of view.—

Charles Darwin (Down, Bromley, Kent).