Charles Darwin, Esq^re My dear Sir,

I do not know whether your attention has ever been called to the peculiar breeds of Sheep found in Aden.² The P. & O. Co ship them on board of their steam-ships for food, and on the passage out I had thus an opportunity of observing them. They are small, pie-bald (almost uniformly), and hairy— They have prominent faces like the Cape and Shanghai sheep, but have large dewlaps before & between the four legs like cows, and their tails are broad and fatty at the base with a short narrow tip bent suddenly downwards. The majority of the rams have no horns, but I saw one with short goat-like horns. I also saw among the herd a larger animal of a brown colour in most respects similar to the pie-bald race, but more goat-like. The hams of this sheep are thin and lanky. I also observed more lanky Indian sheep with flat faces and goat-like horns with brown slightly curled hair. In the face all these sheep are extremely goat-like, but differ in the form of the pupil of the eye from goats. The goats have an indistinct horizontal pupil over which the iris contracts and confuses its form. The sheep on the contrary have a narrow perpendicular pupil. I should think if properly studied by those you have the opportunity, the sheep of the tropics as compared with those of more northern climes, would somewhat assist the theory of transmutation by artificial selection.³

On the subject of usurpation by introduced races I saw some curious instances in Ceylon.⁴ Some 11 years ago I am told a Brazilian plant the Lantana mixta lost⁵ was introduced into the gardens of Ceylon. It has since become scattered through the country, and forms hedgerows for miles along the various roads even into Kandy, being also frequently found in patches on mountains 4000 feet high away from the road. Wherever it grows it spreads fast and seems to paralyse the rest of the plant life. It also occurs, but not so abundantly in the islands of Singapore & Penang.⁶

In all these three islands the Casuarina equisetorum of Australia has also been introduced and is become completely naturalised forming an important feature in the scenery. This tree grows to a good height, and is frequently covered over its trunk with various indigenous species of Ferns.⁷

There is only one other observation to trouble you with and then I have done. In describing a new species of Turdus the other day from the Formosan Mountains the Turdus albiceps mihi, I observed a prominent wart or tubercle on the carpal edge of its wing.⁸ This I thought curious and I immediately examined all the species of the group that I have in my present collection, to wit Oreocincla hancii, mihi Turdus pallidus, Gmel. Garrulax poecilorhynchus et ruficeps, Gould, and Garrulax taiwanus, mihi, all from Formosa, and I found the tubercle perceptible in a degree in them all. Now there is a species I am informed the Turdus dactylopterus, Bonaparte from Syria which has a prominent claw on its carpus.⁹ This then according to the theory expounded by you enables us to understand the existence of the wart in so many species of the same group. I suspect moreover that it occurs in a lesser or greater degree in all the members of the Turdidae, and I have drawn the attention of ornithologists to the fact through the pages of the “Ibis.”¹⁰

I continue at my leisure moments, as you perceive, my researches in Natural History, and I shall be much obliged to you if you can call my attention to any special objects, which I may have the preclusive opportunities to study in these parts for the information of others and for the advancement of science.

I remain | My dear Sir, | Your sincere friend & pupil, | Robert Swinhoe.