The ass varies greatly in colour; and its legs, especially the fore-legs, both in England and other countries--for instance, in China--are occasionally barred transversely more plainly than those of dun-coloured horses. With the horse the occasional appearance of leg-stripes was accounted for, through the principle of reversion, by the supposition that the primitive horse was {63} thus striped; with the ass we may confidently advance this explanation, for the parent-form, the _A. tæniopus_, is known to be barred, though only in a slight degree, across the legs. The stripes are believed to occur most frequently and to be plainest on the legs of the domestic ass during early youth,[141] as is apparently likewise the case with the horse. The shoulder-stripe, which is so eminently characteristic of the species, is nevertheless variable in breadth, length, and manner of termination. I have measured a shoulder-stripe four times as broad as another; and some more than twice as long as others. In one light-grey ass the shoulder-stripe was only six inches in length, and as thin as a piece of string; and in another animal of the same colour there was only a dusky shade representing a stripe. I have heard of three white asses, not albinoes, with no trace of shoulder or spinal stripes;[142] and I have seen nine other asses with no shoulder-stripe, and some of them had no spinal stripe. Three of the nine were light-greys, one a dark-grey, another grey passing into reddish-roan, and the others were brown, two being tinted on parts of their bodies with a reddish or bay shade. Hence we may conclude that, if grey and reddish-brown asses had been steadily selected and bred from, the shoulder-stripe would have been almost as generally and as completely lost as in the case of the horse.