Popular Science Monthly/Volume 57/June 1900/Professor Ewart's Penycuik Experiments

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PROFESSOR EWART'S PENYCUIK EXPERIMENTS.[1]

THE views and works of Darwin have influenced in an unexpected way the nature of the work carried on by biological investigators during the latter end of this fast-dying century. To a great extent, while generally holding the doctrines he held, they have forsaken his methods of inquiry.

If animals and plants have arrived at their present state by descent with modification from simpler forms, it ought to be possible by careful searching to trace the line of ancestry; and it is this fascinating but frequently futile pursuit which has dominated the minds of many of our ablest zoologists for the last thirty years. To such an extent has this pedigree hunting been carried that there is scarcely a group of invertebrates from which the vertebrates have not been theoretically derived; and to-day one of the ablest of our physiologists is using his great powers in the attempt to trace the origin of the backboned animals from a spiderlike creature, and is exercising his ingenuity in a plausible but unconvincing effort to equate the organs of a king-crab with those of a lamprey. This appeal to comparative anatomy and the consequent neglect of living animals and their habits are no doubt partly due to the influence of Huxley, Darwin's most brilliant follower and exponent. He had the engineer's way of looking at the world, and his influence was paramount in many schools. The trend which biology has taken since Darwin's time is also partly due to a fervent belief in the recapitulation theory, according to which an animal in developing from the egg passes through phases which resemble certain stages in the past history of the ancestors of the animal. For example, there is no doubt that both birds and mammals are descended from some fishlike animal that lived in the water and breathed by gills borne on slits in the gullet, and every bird and mammal passes through a stage in which these gill-slits are present, though their function is lost and they soon close up and disappear. In the hope, which has been but partially realized, that a knowledge of the stages through which an animal passes on its path from the ovum to the adult would throw light on the origin of the race, the attention of zoölogists has been largely concentrated on details of embryology, and a mass of facts has already been accumulated which threatens to overwhelm the worker.

The two chief factors which play a part in the origin of species are heredity and variation, and until we know more about the laws which govern these factors we can not hope to arrive at any satisfactory criteria by which we can estimate the importance of the data accumulated for us by comparative anatomists and embryologists. Signs are not wanting that this view is beginning to be appreciated. The publication of 'Materials for the Study of Variation' by Mr. Bateson, a few years ago, shows that there exists a small but active school of workers in this field; and the recent congress on hybridization, held in London under the auspices of the Royal Horticultural Society, is evidence that in America, on the Continent and in Great Britain one of the most important sides of heredity is being minutely and extensively explored. Prof. Cossar Ewart's experiments, which we shall attempt to summarize, deal with heredity and cognate matters, and, although they are so far from complete that the results hitherto obtained can not be regarded as final, they mark an important stage in the history of the subject.

Five years ago Professor Ewart began to collect material for the study of the embryology of the horse, about which, owing to the costliness of the necessary investigations, very little is at present known. At the same time he determined to inquire into certain theories of heredity which have for centuries influenced the breeders of horses and cattle, and the belief in which has played a large part in the production of our more highly bred domestic animals. Foremost among these is the view widely held among breeders that a sire influences all the later progeny of a dam which has once produced a foal to him. This belief in the 'infection of the germ,' or 'throwing-back' to a previous sire, is probably an old one—possibly as old as the similar faith in maternal impressions which led Jacob to place peeled wands before the cattle and sheep of his father-in-law Laban. The phenomenon has recently been endowed with a new name—Telegony. Since the publication of Lord Morton's letter to Dr. W. H. Wollaston, President of the Royal Society, in 1820, it has attracted the attention not only of practical breeders, but of theoretical men of science. The supporters of telegony, when pressed by opponents, having almost always fallen back on Lord Morton's mare, it will be well to recall the chief incidents in the history of this classic animal.

It appears that early in this century Lord Morton was desirous of domesticating the quagga. He succeeded in obtaining a male, but, failing to procure a female, he put him to a young chestnut mare, of seven eighths Arab blood, which had never been bred from before. The result was the production of a female hybrid apparently intermediate in character between the sire and the dam. A short time afterward Lord Morton sold his mare to Sir Gore Ouseley, who bred from her by a fine black Arabian horse. The offspring of this union, which were examined by Lord Morton, were a two-year-old filly and a year-old colt. He describes them as having "the character of the Arabian breed as decidedly as can be expected where fifteen sixteenths of the blood are Arabian, and they are fine specimens of that breed; but both in their color and in the hair of their manes they have a striking resemblance to the quagga." The description of the stripes visible on their coats is careful and circumstantial, but the evidence of the nature of the mane is less convincing: "Both their manes are black; that of the filly is short, stiff, and stands upright, and Sir Gore Ouseley's stud groom alleged that it never was otherwise. That of the colt is long, but so stiff as to arch upward and to hang clear of the sides of the neck, in which circumstance it resembles that of the hybrid."

This is the classical, we might almost say the test, case of telegony: the offspring resembled not so much the sire as an earlier mate of the dam. The facts related tended to confirm the popular view, and that view is widely spread. Arab breeders act on the belief, and it is so strongly implanted in the minds of certain English breeders that they make a point of mating their mares first with stallions having a good pedigree, so that their subsequent progeny may benefit by its influence, even though poorly bred sires are subsequently resorted to.

The evidence of Lord Morton's mare convinced Darwin of the existence of telegony; after a careful review of the case he says "there can be no doubt that the quagga affected the character of the offspring subsequently got by the black Arabian horse." Darwin, however, latterly came to the conclusion that telegony only occurred rarely, and some years before his death expressed the opinion that it was "a very occasional phenomenon." Agassiz believed in telegony. He was strongly of the opinion "that the act of fecundation is not an act which is limited in its effects, but that it is an act which affects the whole system, the sexual system especially; and in the sexual system the ovary to be impregnated hereafter is so modified by the first act that later impregnations do not efface that first impression."

Romanes also believed that telegony occasionally occurred. He paid a good deal of attention to the matter, commenced experiments in the hope of settling the question, and corresponded at length on this subject with professional and amateur breeders and fanciers. The result of his investigations led him to the conclusion "that the phenomenon is of much less frequent occurrence than is generally supposed. Indeed, it is so rare that I doubt whether it takes place in more than one or two per cent of cases." A recent controversy in the Contemporary Review shows us that Mr. Herbert Spencer is a firm upholder of telegony, and that he has a theory of his own as to the mode in which it is brought about. He suggests that some 'germ-plasm' passes from the embryo into the mother and becomes a permanent part of her body, and that this is diffused throughout her whole structure until it affects, among other organs, the reproductive glands. This view, which in some respects recalls the pangenesis of Darwin, is intermediate between the saturation and the infection hypothesis. Professor Ewart refers to it as indirect infection.

Weismann, to whom we owe the term telegony, came to consider the facts for and against its existence in connection with his well-known inquiry into the inheritance of acquired characters. If telegony be true, there is no need to look further for a clear case of the inheritance of a character which has been acquired during the lifetime of the parent. The quagga-ness—if one may be permitted to use such an expression—of Lord Morton's mare was acquired when she was put to the quagga or shortly afterward, and was transmitted to her foals. A clearer case of a character acquired during lifetime and transmitted to offspring could not be imagined. Weismann does not absolutely deny the possibility of the existence of telegony, but he would like more evidence. In the Contemporary Review he writes, "I must say that to this day, and in spite of the additional cases brought forward by Spencer and Romanes, I do not consider that telegony has been proved." And further: "I should accept a case like that of Lord Morton's mare as satisfactory evidence if it were quite certainly beyond doubt. But that is by no means the case, as Settegast has abundantly proved." He would, in fact, refer the case to reversion, and quotes Settegast to the effect that every horse breeder is well aware that the cases are not rare when colts are born with stripes which recall the markings of a quagga or zebra. We shall return to this point later.

A considerable number of German breeders support the contention of Weismann that telegony is as yet unproved, and it may be pointed out that in Germany, on the whole, breeders have had a more scientific education than in England, and that in that country science is regarded with less aversion or contempt than is usually the case among so-called practical men in England. We may mention one more case of an experienced breeder who was equally skeptical—the late Sir Everett Millais, who was, as is well known, an authority of great weight in the matter of dog-breeding. He writes as follows, in a lecture entitled Two Problems of Reproduction: "I may further adduce the fact that in a breeding experience of nearly thirty years' standing, during which I have made all sorts of experiments with pure-blood dams and wild sires, and returned them afterward to pure sires of their own breeds, T have never seen a case of telegony, nor has my breeding stock suffered. I may further adduce the fact that I have made over fifty experiments for Professor Romanes to induce a case of telegony in a variety of animals—dogs, ducks, hens, pigeons, etc.—but I have hopelessly failed, as has every single experimenter who has tried to produce the phenomenon." It is thus evident that there is a considerable body of opinion, both practical and. theoretical, for and against telegony; and that a reinvestigation of the subject is urgently needed. Such a reinvestigation has been begun by Professor Ewart at Penycuik. Since the clearest and most definite evidence of this throwing back to a previous sire is derived from the crossing of different species of the Equidae, it was desirable to repeat the experiment of Lord Morton. This is now unfortunately impossible, because the quagga is extinct. The zebra is, however, still with us, and the mating of a zebra stallion with every variety of horse, pony, and ass, and subsequently putting the dam to pure-bred-sires, has been the more important part of the numerous experiments carried on in the Midlothian village some ten miles southwest of Edinburgh.

PSM V57 D140 Matapo.png
Matapo.

Before considering in detail the result of the experiments it will be necessary to say a few words on the question of the various species of zebra; and since, like Weismann, Professor Ewart explains certain of the phenomena attributed-to telegony by reversion, it will be as well to inquire how far reversion is known among the Equidae, and what evidence we have that the ancestor of the horse was striped.

Matopo, the zebra stallion from which Professor Ewart had up to last midsummer bred eleven zebra-hybrids from mares of various breeds and sizes, belongs to the widely distributed group of Burchell's zebras. Many subspecies or varieties are included in this group, which, as regards the pattern of the stripes, passes—in certain varieties found in Nyassaland—into the second species, the mountain zebra, once common in South Africa. The third species is the Grévy's zebra of Shoa and Somaliland; it is probably this species which attracted so much attention in the Roman amphitheaters during the third century of our era. A pair of Somali zebras has recently been presented to the queen by the Emperor Menelik, and is now lodged in the Zoological Gardens, Regent's Park. The species measures about fifteen hands high, is profusely striped, and stands well apart from the other two groups. It is important to note that, in Professor Ewart's opinion, it is the most primitive of all the existing striped horses.

There is no direct evidence that the ancestors of horses were striped. Certain observers think that some of the scratches on the lifelike etchings on bone, left us by our palæolithic cave-dwelling ancestors, indicate such stripes, but little reliance can be placed on this. On the other hand, there is much indirect evidence. Every one who has an eye for a horse, and who has traveled in Norway, is sure to have noticed the stripings, often quite conspicuous, on the dun-colored Norwegian ponies. Colonel Poole assured Darwin that the Kattiawar horses had frequently "stripes on the cheeks and sides of the nose." Breeders are well aware that foals are often born with stripes, usually on the shoulders or legs, less frequently on the face. Such stripes, as a rule, disappear as the colt grows up, but can often be detected in later life for a short time after the coat has been shed; they are sometimes only visible in certain lights, and then produce somewhat the same impression as a watered silk. From the facts that more or less striped horses are found all over the Old World; that in Mexico and other parts of America the descendants of horses which were introduced by the Spaniards and which afterward ran wild are frequently dun-colored and show stripes; that foals are frequently striped; and that mules not uncommonly have leg and shoulder stripes, the inference is largely justified that the ancestors of all our horses were striped.

We now pass to the experiments made at Penycuik in crossing the zebra Matopo with various mares of different breeds: 1. Matopo was first mated with Mulatto, one of Lord Arthur Cecil's black West Highland ponies. The result was the hybrid Romulus (see p. 132), which on the whole, both in mental disposition and bodily form, takes more after his father than his mother. His striping is even more marked than that of his sire. He has a semi-erect mane which has been shed annually. The pattern of the markings, on both body and face, resembles the stripes on a Somali zebra—which, as we have seen, is regarded by Professor Ewart as the most primitive type—more than they resemble that of any of Burchell's zebras. The profuse striping is a point of difference between this hybrid and Lord Morton's. The quagga-hybrid was less striped than many dun-colored horses.

The mother Mulatto was next mated with a highly bred gray Arab horse, Benazrek. The offspring agrees in all respects with ordinary foals; it had, however, a certain number of indistinct stripes, which could only be detected in certain lights. The stripes were not nearly so clear as in a foal bred by Mr. Darwin from a cross-bred bay mare and a thoroughbred, and they disappeared entirely in about five months.

Recently Mulatto has produced a third foal to Loch Corrie, a sire belonging to the Isle of Rum group of West Highland ponies, and closely resembling his mate. This foal was about as much striped as its immediate predecessor. In both cases the pattern of the stripe differed not only from that of Matopo, the previous sire, but from that of the hybrid Romulus. These two foals seem to lend some support to telegony;

PSM V57 D142 Romulus at twenty seven days.png
Romulus, Twenty-seven Days Old.

but the evidence which might be drawn from the second of them is destroyed by the fact that the sire Loch Corrie has produced foals from two West Highland mares, one brown and one black, and each of these foals has as many and as well marked stripes as the foal of Mulatto.

2. Four attempts were made to cross the zebra with Shetland ponies; only one succeeded. The hybrid was a smaller edition of Romulus. The dam Nora had been bred from before, and had produced, by a black Shetland pony, a foal of a dun color which was markedly striped. After the birth of the hybrid she was put to a bay Welsh pony; the resulting foal had only the faintest indication of stripes, which soon disappeared. It is a remarkable fact that Nora's foals were more striped before she had been mated with the zebra than afterward.

3. Five Icelandic ponies were mated with Matopo, of whom one produced, in 1897, a dark-colored hybrid. The dam, Tundra, was a yellow and white skewbald which had previously produced a light bay foal to a stallion of its own breed. Her third foal (1898) was fathered by a bay Shetland pony, and in coloration closely resembled its dam. There was no hint of infection in this case. This year Professor Ewart has bred from this mare, by Matopo, a zebra-hybrid of a creamy-fawn color, and so primitive in its markings that he believes it to stand in much the same relation to horses, zebras, and asses as the blue-rock does to the various breeds of pigeons (see illustration).

PSM V57 D143 Iceland pony and her hybrid foal.png
Tundra (an Iceland Pony), her Foal, Circus Girl (born 1898), and her Hybrid Foal, Sir John (by Matopo), when a Month Old (born 1899).

4. Two Irish mares, both bays, produced hybrids by Matopo, and subsequently bore pure-bred foals. One of the latter was by a thoroughbred horse, the other by a hackney pony. The foals were without stripes, and showed no kind of indication that their mother had ever been mated with a zebra.

5. Although Professor Ewart experimented with seven English thoroughbred mares and an Arab, he only succeeded in one case. The mare produced twin hybrids, one of which unfortunately died immediately after birth. This summer the same mare has produced a foal to a thoroughbred chestnut; "neither in make, color, nor action" does it in any way resemble a zebra or a zebra-hybrid.

6. A bay mare which had been in foal to Matopo for some months miscarried. Here—if there is anything in the direct infection theory—the unused germ-cells of the zebra had a better chance than usual of reaching the ova from which future offspring are to arise, yet neither of the two foals which this mare subsequently produced to a thoroughbred horse "in any way suggests a zebra."

The above is the record of the successful experiments which have been tried at Penycuik, with a view of throwing light on the existence of telegony in the Equidae. Experiments have also been made with other animals, such as rabbits, dogs, pigeons, fowls, and ducks. Space allows us to quote but one. Six white doe rabbits, all of which had borne pure white offspring to white bucks, were crossed with wild brown rabbits. The result was forty-two young rabbits, all of a bluishblack color, which in a very short time turned to a brown. These, at the time of writing, were about half grown, and Professor Ewart. tells us that it is almost impossible to distinguish them from a full-blooded wild rabbit kept in the same inclosure. The half-breeds, however, were tamer and slightly lighter in color.' The mother does next bred with white bucks again, and in every case bred true. The pure white young showed no trace of throwing back to a previous sire.

A phenomenon somewhat similar to telegony, and one which seems at present quite unexplained, is that a hen which has been crossed with a cock of another breed often lays eggs whose shell is no longer like that of its own breed, but in color, and frequently in texture, resembles that of the breed with which it has been crossed. When one calls to mind that the shell is deposited by a special shell-gland which is in no way connected with the ovary, but is a part of the quite distinct oviduct, and that the change in the color of the eggshell must be caused by some change brought about in this gland by crossfertilization, we begin to recognize how mysterious and inexplicable are many of the problems which affect breeding.

Throughout his account of his experiments Professor Ewart is extremely cautious in claiming to prove anything, but we think he has justified his claim to have shown that telegony by no means always occurs, as many breeders believe. His experiments so far support the view of Continental mule breeders, that telegony, if it takes place, occurs very seldom. But the experiments are not complete, and it is much to be hoped that they may be continued. If it should subsequently appear that out of fifty pure-bred foals from dams which have been previously mated with the zebra no single instance of telegony be found, the doctrine may surely be neglected by breeders; and if in the experiments which are now being carried out with various other mammals and birds telegony does not occur, the doctrine may be relegated to the 'dumping-ground' of old superstitions. The present state of the matter may be summed up in the professor's own words: "The experiments, as far as they have gone, afford no evidence in support of the telegony hypothesis." Nothing has occurred which is not explicable on the theory of reversion.

There is no factor in breeding of more importance than prepotency, and none which is more difficult to estimate. The term is necessarily a relative one, and, further, it may affect some characters and not others. Often it must go undetected, as in the case of the leader of a herd of wild cattle, who may be highly prepotent, but whose prepotency, unless he is mated with members of another herd displaying different characters, may pass unnoticed. Breeders claim to be able to produce cattle so prepotent that they will produce their like, however mated. A well-known dealer in highly-bred ponies used to boast that he had a filly so prepotent that, though she were sent to the best Clydesdale stallion in Scotland, she would throw a colt showing no cart-horse blood. Prepotency is usually obtained by inbreeding, which up to a certain point fixes the character of a race, and in all cases tends to check variation and reversion—the Jews, for instance, as a race are strongly prepotent—but there is no doubt that it may also arise as a sport, and this is probably its more usual origin in a state of Nature. Professor Ewart, however, believes that inbreeding is much commoner among wild animals than has usually been conceded, and he holds the opinion that the prepotency so induced has played a considerable part in the origin of species. This, if true, would to some extent take the place of Romanes' 'physiological selection'; for Romanes also thought that, though of great importance, variation and natural selection were insufficient to account for the origin of species without some factor which would help to mitigate the swamping effect of intercrossing—some such agency as the fences of modern farms and cattle ranches—without which the famous cattle breeds of the world would soon disappear in a general 'regression toward mediocrity.'

In inbreeding the great difficulty of the breeder is to know when to stop. Carried too far it undoubtedly leads to degeneracy. In the 'Domesticated Animals of Great Britain,' Low records the case of a gentleman who inbred foxhounds to such an extent that "the race actually became monstrous and perished." Hogs, if too closely inbred, grow hair instead of bristles; their legs become short and unable to support the body; and not only is their fertility diminished, but the mothers can not nourish the young.

So far as is known, no direct investigations have been made to test how far inbreeding may be carried in the Equidae; but, on the other hand, the breeding of race-horses may perhaps be looked upon as a gigantic experiment in this direction. Our English thoroughbreds can be traced back to a few imported sires—the Byerly Turk, imported in 1689; the Darley Arabian, in 1710; and the Godolphin Arabian, in 1730. Since then, by careful breeding and nutrition, they have increased on an average some eight or nine inches in height. There is, however, a widely spread impression that at present there is a marked deterioration in the staying power and in the general 'fitness 1 of the racer. The falling off is further shown by a fact commented on by Sir Walter Gilbey—viz., "the smallness of the percentage of even tolerably successful horses out of a prodigious number bred at an enormous outlay." In support of this he quotes a sentence from the Times (December 27, 1897), referring to a sale in which thirty-two yearlings had been sold for 51,250 guineas: "These thirty-two yearlings" (said the Times) "are represented by two winners of five races, Florio Rubattino and La Reine, who have contributed about 2.000l. to the cotal cost; and there is not, so far as can be known, a single one of the thirty others with any prospect of making a race-horse."

If, then, it is true that the English race-horse is on the down grade, what steps should be taken to arrest this descent? Sir Everett Millais restored a pack of basset hounds by crossing them with a bloodhound, the original forefather of bassets. The resulting pups were bassets in form, but not quite bassets in color; when, however, these cross-breeds were mated with bassets the majority of the pups turned out to be perfect bassets both in shape and coloration. This indicates that one way to rejuvenate the race-horse would be to have recourse to a new importation of the best Arab mares that the plains of Arabia can produce. Breeders hesitate to adopt this course, because their present breed is not only larger but, over very short distances, fleeter than its forefathers. The shortening of the course in recent years is probably a further sign of the degeneracy of our present racers. Were new blood introduced and more three-or four-mile races instituted, we should doubtless soon have a return to the champion form of bygone days. Another method would be to import some of the racers of Australia or New Zealand and cross them with the home product. Different surroundings, food, etc., soon influence the constitution, and this being so, it would be advisable to select those horses of pure descent which have been longest subjected to these altered conditions. Thus the chance of reversion occurring would be increased.

It has been noticed more than once in the preceding pages that a young animal showing reversion is strong and vigorous. It is the belief of dog breeders that those members of an inbred litter which show reversion are the strongest and best. Similarly, experience shows that if an inbred sire and dam produce a dun-colored striped foal it almost always turns out well. Reversion is accompanied by a rejuvenescence; it is as though the young animal had appeared at an earlier period in the life history of the race, before the race had undergone those changes in the way of deterioration which so often accompany inbreeding.

Wild animals are frequently thought to be prepotent over tame ones, but of the eleven zebra-hybrids bred at Penycuik only two took markedly after their sire, the zebra Matopo.[2] There are other experiments recounted which tell the other way, and at present this matter remains in a state of considerable uncertainty.

This article must not close without a word or two more about the zebra-hybrids. It is mentioned above that only two out of the eleven which have already been born took, strongly after their father.

PSM V57 D147 Romulus and matapo.png
Romulus. Matopo.

Those who have seen the young hybrids playing about in the fields at Penycuik must agree that they are the most charming and compactly built little animals possible. Of Romulus, the eldest of the herd, Professor Ewart says: "When a few days old [he] was the most attractive little creature I have ever seen. He seemed to combine all the grace and beauty of an antelope and a well-bred Arab foal. . . . What has struck me from the first has been his alertness and the expedition with which he escapes from suspicious or unfamiliar objects. When

quite young, if caught napping in the paddock, the facility with which he, as it were, rolled on to his feet and darted off was wonderful."

The writer can fully confirm all the praise Professor Ewart lavishes on his pets; in truth, Romulus has been well described as a "bonnie colt with rare quality of bone. . . and with the dainty step and the dignity of the zebra." Remus, the offspring of the Irish mare, has been from the first more friendly than his half-brother; he objected less to the process of weaning, and, if he survives, promises to be the handsomest and fleetest of the existing hybrids.

On the whole, the hybrids are unusually hardy; only two have been lost—one, a twin, which died almost as soon as it was born, and another which lived some three months and then succumbed. It is only fair to say that the dam of the latter, who was only three years old when the hybrid was born, had been much weakened by attacks of the strougylus worm, and that she was the victim of close inbreeding. Both the zebras and the hybrids which have been under observation at Penycuik show a remarkable capacity for recovering from wounds. Accidental injuries heal with great rapidity. On one occasion the surviving twin was discovered with a flap of skin some five inches long hanging down over the front of the left fetlock. The skin was stitched into its place again, during which operation the little hybrid fought desperately and cried piteously; but it soon recovered, the wound healed, and now scarcely a scar remains. There was no lameness and no swelling either at the fetlock or above the knee. About a year ago four hybrid colts and three ordinary foals were attacked by that scourge of the stable, the strongylus worm. One of the latter died and another was reduced almost to a skeleton; the hybrids, though obviously affected, suffered much less than the others and soon recovered. It is further noticeable that the hybrids suffer less from colds and other slight ailments than the mares and horses among which they live.

There is no doubt that it is a comparatively easy matter to breed these hybrids, and that they are not only extremely attractive animals to the eye, but hardy and vigorous, possessed of great staying powers, and promising to be capable of severe work.

From what we have said, it is evident that the Penycuik experiments are of the highest interest, both practical and theoretical, and the public spirit and self-devotion shown by the Edinburgh professor in carrying them out can not be too widely recognized.

  1. Abstract from an article in the Quarterly Review discussing Professor Ewart's 'Experimental Investigations on Telegony,' read before the Royal Society last year, and his book, 'The Penycuik Experiments,' published by Messrs. A. & D. Black.
  2. The illustration shows the difference between the facial marks of the zebra and those of the hybrid. The latter, in this respect, bears much the same relation to the former as a blue-rock pigeon does to a fancy type.