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 



