CHAP. V.] ANALOGOUS VARIATIONS. 119 



tint, and which would not probably have all appeared together 

 from simple variation. More especially we might have inferred 

 this, from the blue colour and the several marks so often appear- 

 ing when differently coloured breeds are crossed. Hence, although 

 under nature it must generally be left doubtful, what cases are 

 reversions to formerly existing characters, and what are new but 

 analogous variations, yet we ought, on our theory, sometimes to 

 find the varying offspring of a species assuming characters which 

 are already present in other members of the same group. And 

 this undoubtedly is the case. 



The difficulty in distinguishing variable species is largely due 

 to the varieties mocking, as it were, other species of the same 

 genus. A considerable catalogue, also, could be given of forms 

 intermediate between two other forms, which themselves 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 assumed somfi 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 an allied species. I have collected a long 

 list of such cases ; but here, as before, I lie under the great dis- 

 advantage of not being able to give them. I can only repeat that 

 such cases certainly occur, and seem to me very remarkable. 



I will, however, give one curious and complex case, not indeed 

 as affecting any important character, but from occurring 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 actually 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 England 

 of the spinal stripe in horses of the most distinct breeds, and 



