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,
Equus (comics) to them. Eventually, Superman tracks all the victims of the Vanishing to Metropia, an artificial paradise within the Phantom Zone, where he again encountered Equus, who has allied himself with General Zod, who is on a campaign to destroy Metropia. Equus, whose chestplate bears the Roman numeral "III", was the third version of a program to create super-soldiers. Equus, or "Vee Three" as he was designated, is said to be psychotic, due to the enlargement of the amygdalae to which the OMAC candidates were subjected. Equus III later appears in "Titans/Outsiders Secret Files 2005", stored alongside the Wildebeest, who had