Under this point of view, the horse, the zebra, and the ass, are all of the same family. If the horse is the source, or principal trunk, the zebra and the ass will be collateral branches. The number of their resemblances being infinitely greater than that of their differences, we may look on them as constituting only one genus, the principal characters of which are clearly announced, and common to all three. They are the only animals which have solid hoofs without any appearance of toes or nails. Though they form three very distinct species they are not absolutely separated, since the male-ass will produce with the mare, and the horse with the she-ass; and it is probable that if we were to tame the zebra, and mollify his savage nature, it would likewise produce with the horse and the ass. This mule, therefore, which has hitherto been regarded as a vitiated production, as a monster composed of two different natures, and consequently incapable of reproduction, is not so base as might be imagined from the above prejudice, since it is not really unprolific, and its sterility depends on certain external and peculiar circumstances. It is well known that mules produce in warm countries, and we have some examples of their producing even in our temperate climates. But we do not know whether this generation ever proceeded from the union of a male with a female mule, or whether the production were not effected by the junction of a male with a mare, or a male-ass with a mule. There are two kinds of males, the first is the great mule, which proceeds from the junction of a male-ass with a mare, and the small mule, proceeding from the horse and the she-ass, which we shall call _bardeau_, to distinguish it from the other. The ancients were acquainted with both, and distinguished them by two different names; they called the first _mulus_, and the second _hinnus_. They assert that the _mulus_ produced with the mare, an animal called _ginnus_[AH], or _hinnus_; that the she-mule conceived very readily, but seldom brought the foetus to perfection: and that, though they have had frequent examples of mules bringing forth, yet such productions were looked on as prodigies. But what is a prodigy of nature, except an event which happens more rarely than some others? The he-mule, therefore, can engender, and the female conceive, and bring forth, in certain circumstances: hence it is only required to know what these circumstances are, and to acquire further information concerning degeneration by a mixture of species, and consequently on the unity and diversity of each genus. To succeed in these enquiries, the he-mule must be joined with a she-mule, a mare, and a she-ass; the same should be done with the bardeau, and then the result of these six copulations ought to be carefully marked. The females of the ass, mule, and bardeau, should also be paired with a horse.