Sanson and Pietrement viewed with suspicion Prejvalsky's discovery, and Pietrement placed the animal under the same subspecies of Equus with Equus caballus. In this country Dr Sclater took the same view as Poliakoff, whilst Sir W. Flower thought that it might be an accidental hybrid between a Kiang and a Mongolian or some other kind of horse. Flower's caution was quite justifiable at a time when only a single skin was known, although it seems not very likely that such accidental unions as he postulated would occur between different species of Equidae in a state of nature, in view of the well-known objection of the herds of half-wild horses in the Caucasus to intermix in any way. Yet, though many specimens both living and dead, which have since come to hand, render it very improbable that Prejvalsky's horse is a mule, the theory has retained its hold upon some naturalists down to the present time, who, however, have made no attempt to test the theory by experiment.

It is to the indefatigable energy and enthusiasm of Professor Cossar Ewart, who has done more than any living man to advance our knowledge of the Equidae, that we owe the experiments which seem likely to settle the question finally. It is best to let him speak for himself [The Wild Horse " (Equus przewalskii Poliakoff), Proc. Royal Soc. of . Edinburgh, 1903, pp. 460-8] " With the help of Lord Arthur Cecil I succeeded early in 1902 in securing a male wild Asiatic ass [This animal, now in the Zoological Garden, Regent's Park, is an onager indicus ( = hemionus indicus, cf. p. 43)] and a couple of Mongolian pony mares one a yellow dun, the other a chestnut. 'Jacob,’ the wild ass, was mated with the dun Mongol mare, with a brownish- yellow Exmoor pony, and with a bay Shetland-Welsh pony. The chestnut Mongol pony was put to a light grey Connemara stallion. Of the four mares referred to three have already (June) foaled, namely the Exmoor and the two Mongolian ponies. The Exmoor having foaled first, her hybrid may be first considered. It may be mentioned that the Exmoor pony had in 1900 and again in 1901 a zebra hybrid, the sire being the Burchell zebra ( Matopo (Fig. 36) used in my telegony experiments. In the case of her Kiang hybrid the period of gestation was 335 days (one day short of what is regarded as the normal time), but she carried her 1900 zebra hybrid 357 days, three weeks beyond the normal time. The Exmoor zebra hybrids are as nearly as possible intermediate between a zebra and a pony ; the Kiang hybrid, on the other hand, might almost pass for a pure-bred wild ass. In Mendelian terms the Exmoor pony proved recessive, the wild ass dominant. In zebra hybrids the ground colour has invariably been darker than in the zebra parent; but the Kiang hybrid is decidedly lighter in colour than her wild sire, while in make she strongly suggests an Onager the wild ass so often associated with the Runn of Cutch. Alike in make and colour the Kiang hybrid differs from a young Prejvalsky foal." This comparison Professor Ewart was enabled to make by means of his hybrid foal with the skin of a very young Prejvalsky foal (for which he was indebted to Mr Carl Hagenbeck).

" I have never seen a new-born wild horse ; but if one may judge from the conformation of the hocks, from the coarse legs, big joints, and large head of the yearlings to their close resemblance to dwarf cart-horse foals it may be assumed they are neither characterized by unusual agility nor fleetness. The Kiang hybrid, on the other hand, looks as if built for speed, and almost from the moment of its birth has by its energy and vivacity been a source of considerable anxiety to its by no means placid Exmoor dam. When four days old it walked over twenty miles ; on the fifth day instead of resting it was unusually active, as if anxious to make up for the enforced idleness of the previous evening. In the hybrid the joints are small, and the legs long and slender, and covered with short, close-lying hair. In the wild horse the joints are large, and the 'bone' is round as in heavy horses.

" As to its colour it may especially be mentioned that the hybrid has more white around the eyes than the wild horse, but is of a darker tint along the back and sides and over the . hind-quarters. Too much importance, however, should not be attached to differences in colour; for though the two hybrid foals, which have already arrived, closely agree in their colora tion, subsequent foals may differ considerably, and it is well known that young wild horses from the western portion of the Great Altai mountains differ in tint from those found further east. Of more importance , than the coat-colour is the nature of the hair. A Prejvalsky foal has a woolly coat not unlike that of an Iceland foal. In the hybrid, the hair is short and fine and only slightly wavy over the hind-quarters. It thus differs but little from a thoroughbred or Arab foal.

"The mane and the tail of the hybrid are exactly what one would expect in a mule ; the dorsal band, 75 mm. wide over the croup in the sire, has in the hybrid a nearly uniform width of 12 mm. from its origin at the withers until it loses itself halfway down the tail. The tail, which differs but little from that of a pony foal, is of a lighter colour than the short, upright mane, while the dorsal band is of a reddish-brown hue. In the wild horse the dorsal band is sometimes very narrow (under 5 mm.) and indistinct. In the Kiang sire there are pale, but quite distinct stripes above and below the hocks, and small faint spots over the hind -quarters vestiges apparently of ancestral markings ; but in the hybrid there are neither indications of stripes across the hocks or withers, nor spots on the quarters. In having no indications of bars on the legs, or faint stripes across the shoulders, the hybrid differs from Prejvalsky colts ; it also differs in having a longer flank feather and in the facial whorl being well below the level of the eyes. As in the Kiang and some of the wild horses, the under surface of the body and the inner aspect of the limbs are nearly white.

" In the hybrid the front chestnuts (wrist callosities) are smooth and just above the level of the skin; but instead of being roughly pear-shaped, as in the Kiang, they are somewhat shield-shaped, as in the Onager. In the wild horse the front chestnuts are elongated. In the Exmoor dam the hind chestnuts (hock callosities) are 27 mm. in length and 10 mm. wide. In the sire there is a minute callosity inside the right hock. In the hybrid the hind chestnuts are completely absent. In the absence of hock callosities the hybrid differs from the wild horse, in which they are relatively longer than Clydesdales, Shires, and other heavy breeds of horses. In the hybrid, as in the sire and dam, there are smooth, rounded fetlock callosities (ergots) on both fore and hind limbs.

" In the wild horses the hoof is highly specialized, the 'heels' being bent inwards (contracted) to take a vice-like grip of the frog. In the hybrid the hoof closely resembles that of the pony dam ; it is shorter than in the Kiang, and less contracted at the * heels ' than in the wild horse. The Kiang hybrid further differs from a young wild horse in the lips and muzzle, the nostrils and ears, and in the form of the head and hind- quarters. The wild horse has a coarse, heavy head, with the lower lip (as is often the case in large-headed horses and in Arabs with large hock callosities) projecting beyond the upper. The nostrils in their outline resemble those of the domestic horse, while the long, pointed ears generally project obliquely outwards, as in many heavy horses and in the Melbourne strain of thoroughbreds. Further, in the wild horse the forehead is convex from above downwards, as well from side to side, hence Prejvalsky's horse is sometimes said to be ram-headed. In the hybrid the muzzle is fine as in Arabs, the lower lip is decidedly shorter than the prominent upper lip, the nostrils are narrow as in the Kiang : and even at birth the forehead was less rounded than is commonly the case in ordinary foals. The ears of the hybrid, though relatively shorter and narrower than in the Kiang, have, as in the Kiang, incurved dark-tinted tips, and they are usually carried erect or slightly inclined towards the middle line. In the wild horse the croup is nearly straight and the tail is set on high up as in many desert Arabs. In the hybrid the croup slopes as in the Kiang and in many ponies, with the result that the root of the tail is on a decidedly lower level than the highest part of the hind-quarters. Further, in the young wild horses I have seen the heels (points of the hocks) almost touch each other, as in many Clydesdales, and the hocks are distinctly bent. In the hybrid the hocks are as straight as in well-bred foals, and the heels are kept well apart in walking. Another difference of considerable importance is, that while the wild horse neighs, the hybrid makes a peculiar barking sound remotely suggestive of the rasping call of the Kiang.

"The dun Mongol pony's hybrid arrived five weeks before its time, and, though perfect in every way, was short-lived. Only in one respect did this hybrid differ from the one already described. In the Ex moor hybrid the hock callosities are entirely absent ; in the Mongol hybrid the right hock callosity is completely wanting, but the left one is represented by a small, slightly hardened patch of skin, sparsely covered with short white hair. In zebra hybrids out of cross-bred mares the hock callosities are usually fairly large, while in hybrids out of well-bred pony mares the hock callosities are invariably absent. The Exmoor pony [The Exmoor ponies are said to have derived some good blood from a famous stallion Katerfelto], though not as pure as the Hebridean and other ponies without callosities, has undoubtedly a strong dash of true pony blood; the Mongol pony is as certainly saturated with what, for want of a better term, may be called cart-horse blood."

Prof. Ewart thus sums up the results of his experiment : " From what has been said, it follows that a Kiang-Mongol pony hybrid differs from Prejvalsky's horse

(1) in having the merest vestiges of hock callosities ;
(2) in not neighing like a horse ;
(3) in having finer limbs and joints and less specialized hoofs ;
(4) in the form of the head, in the lips, muzzle, and ears;
(5) in the dorsal band ; and (6) in the absence even at birth of any suggestion of shoulder stripes and of bars on the legs."

After this experiment it does not seem likely that zoologists will continue to hold that Prejvalsky horses are the offspring of Kiangs and feral Mongolian ponies [As these pages are passing through the press the Prejvalsky horses belonging to the Duke of Bedford have themselves triumphantly refuted the charge of their being merely mules by having this year (1904) produced offspring] . But as some naturalists had maintained that Prejvalsky horses in nowise differed essentially from an ordinary horse and held that the colts brought from Central Asia were the progeny of escaped feral Mongol ponies, and as others again asserted that they failed to discover any difference between the young wild horses in the London Zoological Gardens and Iceland ponies of a like age, Prof. Ewart again resorted to the experimental method.

To test the first of these assertions he mated his chestnut Mongol pony with a young Connemara stallion; to test the second he purchased an Iceland mare in foal to an Iceland stallion. " The chestnut Mongol mare produced a foal the image of herself. The foal, it is hardly necessary to say, decidedly differs from the Prejvalsky colts recently imported from Central Asia by Mr Hagenbeck, and it decidedly differs from the wild ass hybrids described above. The Iceland foal, notwithstanding the upright mane and the woolly coat, for a time of a nearly uniform white colour, could never be mis- taken for a wild horse, and the older it gets the difference will become accentuated."

"If the Prejvalsky horse is neither a wild ass-pony mule nor a feral Mongolian pony, and if moreover it is fertile (and its fertility can hardly be questioned), I fail to see how we can escape from the conclusion that it is as deserving as, say, the Kiang to be regarded as a distinct species ."

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