Page - 171 - in The Origin of Species

SPECIFIC CHARACTERS HIGHLY VARIABLE 171 selves can only doubtfully be ranked as species; and this shows, unless all these closely allied forms be considered as independently created species, that they have in varying as- sumed some of the characters of the others. But the best evidence of analogous variations is afforded by parts or organs which are generally constant in character, but which occasionally vary so as to resemble, in some degree, the same part or organ in all species. I have collected a long list of such cases; but here, as before, I lie under the great disadvantage of not being able to give them. I can only re- peat that such cases certainly occur, and seem to me very re- markable. I will, however, give one curious and complex case, not indeed as affecting any important character, but from occur- ring in several species of the same genus, partly under domestication and partly under nature. It is a case almost certainly of reversion. The ass sometimes has very distinct transverse bars on its legs, like those on the legs of the zebra: it has been asserted that these are plainest in the foal, and, from inquiries which I have made, I believe this to be true. The stripe on the shoulder is sometimes double, and is very variable in length and outline. A white ass, but not an albino, has been described without either spinal or shoulder stripe : and these stripes are sometimes very obscure, or actu- ally quite lost, in dark-coloured asses. The koulan of Pallas is said to have been seen with a double shoulder-stripe. Mr. Blyth has seen a specimen of the hemionus with a distinct shoulder-stripe, though it properly has none ; and I have been informed by Colonel Poole that the foals of this species are generally striped on the legs, and faintly on the shoulder. The quagga, though so plainly barred like a zebra over the body, is without bars on the legs; but Dr. Gray has figured one specimen with very distinct zebra-like bars on the hocks. With respect to the horse, I have collected cases in Eng- land of the spinal stripe in horses of the most distinct breeds, and of all colours: transverse bars on the legs are not rare in duns, mouse-duns, and in one instance in a chestnut ; a faint shoulder-stripe may sometimes be seen in duns, and T have seen a trace in a bay horse. My son made a careful examination and sketch for me of a dun Belgian cart-horse