Horse outward similarity is an unreliable measure of relatedness. Besides the horse, there are six other species of genus "Equus" in the Equidae family. These are the ass or donkey, "Equus asinus"; the mountain zebra, "Equus zebra"; plains zebra, "Equus quagga"; Grévy's zebra, "Equus grevyi"; the kiang, "Equus kiang"; and the onager, "Equus hemionus". Horses can crossbreed with other members of their genus. The most common hybrid is the mule, a cross between a "jack" (male donkey) and a mare. A related hybrid, a hinny, is a cross between a stallion and a jenny (female donkey). Other hybrids include the zorse,
The Horse and the Donkey The Horse and the Donkey The Horse and the Donkey is a variant of a fable type recorded since antiquity of which there is scarcely one version that concerns the same pair of animals. Included as one of Aesop's Fables and numbered 181 in the Perry Index, its Greek sources also include a donkey and a mule, while the story is told of an ox and a donkey in the Mediaeval Latin version of Ademar. In the former the overburdened donkey asks its companion for help in carrying its load and dies when this is refused; the other is then