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 Equidæ. 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 bluish-black colour, 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 was almost impossible to distinguish them from a full-blooded wild rabbit kept in the same enclosure. The half-breeds, however, were tamer and slightly lighter in colour. 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 colour, and frequently in texture, resembles that of the breed with which it has been crossed. Mr. Bulman has recorded a case of this in the pages of ‘Natural Science.’ Some Orpington fowls which laid eggs of a buff tint were allowed to run loose in a large yard with fowls of various breeds. After a few months they were confined in separate pens again, and for several weeks afterwards they continued to lay white eggs. There seems to be no doubt of the existence of this curious phenomenon; it is mentioned by Gadow in his volume on ‘Birds,’ in Bronn’s ‘Thierreich,’ by Nathusius in the Journal für Ornithologie, and in Newton’s ‘Dictionary of Birds.’ 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 colour of the eggshell must be caused by some change brought about in this gland by cross-fertilization, 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 what the Americans would term 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.
Partly owing to a certain doubt or distrust which has recently been expressed as to the existence of reversion, and no doubt partly because it is reasonable to hold that the phenomena of telegony may all be referred to reversion, Professor Ewart has made some direct experiments on this subject. Darwin, Tegetmeier, and many others have made numerous breeding experiments on pigeons, with the result that we may say that the crossing of extreme forms usually tends to reversion in the offspring. The ancestor of the domestic pigeon is known with tolerable certainty to have been the blue-rock pigeon, Columba livia. By crossing a male barb-fantail and a female barb-spot Darwin produced a bird ‘which was hardly distinguishable from the wild Shetland species’ of blue-rock. In his description of this experiment, Darwin, as Weismann points out, confines himself chiefly to the coloration: he does not inquire how far reversion also appears in the structure of the bird. This question has been answered by one of Professor Ewart’s many experiments with pigeons. He crossed a white fantail cock with the offspring of an owl and an archangel. The fantail was pure white, with thirty feathers in its tail, and was so prepotent as to produce white offspring when mated with blue pouters. The owl-archangel was more of an owl than an archangel. One of the young of this complex pair had the coloration of the Shetland rock pigeon, which has a white croup and the wings in front of the bars a uniform blue; the other resembled the Indian rock pigeon in having a blue croup and the front part of the wings chequered. In this second bird there was complete reversion as to colour, and in the first, wherever measurements were possible, there was practically complete reversion also as to form. ‘In its measurements it is relatively almost identical with a typical Shetland blue-rock.’ The tail feathers are twelve in number, and show but the faintest indications of any colour-inheritance from their immediate parents. An additional point of interest is that in disposition this bird seems wilder and more shy than the domesticated breeds usually are. It is vigorous and hardy, and is much admired by the fanciers.
Another bird whose wild ancestor is known with a high degree of certainty is the barn-door fowl. It has sprung from the jungle fowl, Gallus bankiva, and less remotely from the game fowl. Hence, if fowls of different breeds are crossed, the offspring, should reversion occur, ought to resemble either the jungle fowl or their less remote ancestors, the game fowl. A dark red-breasted bantam was crossed with an Indian game Dorking; of the nine chickens which resulted, six resembled Dorkings, and three in both form and colour resembled game birds. Two of the three grew up, and the only visible trace of their parentage was a double comb inherited from their cross-bred father. Here again the reversion does not stop at the colour and form, but extends to disposition; the birds are very shy, and fly about like wild birds. The above are but two instances out of many which might be quoted from the Penycuik experiments; they are, however, unusually clear cases, and should do something to restore confidence amongst recent doubters of reversion.
An animal is said to be prepotent when it strongly impresses its own peculiarities of form, colour, temperament, etc., on its offspring. In the above-mentioned experiment with pigeons the owl had been prepotent over the archangel in the mother of the offspring which showed such marked reversion. There is no factor in breeding of more importance than prepotency, and none which it 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 towards 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,’ Lowe 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 cannot nourish the young. That infertility is induced by inbreeding is further shown by some experiments of Ritzema Bos with rats. From seven rats of one family and an unrelated male he continued inbreeding for a period of some six years, and bred about thirty generations. The average of the numbers in each litter fell from 7½ in 1887 to 47/12 in 1891 and 3⅕ in 1892. Further, the offspring of inbred parents are usually weak. Sir Everett Millais estimated that 60 to 70 per cent. of inbred dogs attacked by distemper were carried off.
On the other hand, inbreeding often succeeds even when carried to what the ordinary man would consider excess. The ‘Herd-book’ contains the following case in point. The bull Bolingbroke and the cow Phœnix were more closely related to one another than half-brother is to half-sister. They were mated, and produced the bull Favourite. Favourite was then coupled with his dam, and produced the cow Young Phœnix; he was then coupled with his daughter Young Phœnix, and the world-famed Comet was the result. Professor Ewart tells us that if there was little crossing in the production of Comet, there was still less in that of Clarissa, the mother of the celebrated Restless. An instance of the faith in close inbreeding which exists in the minds of breeders occurred in a letter which the Field published in 1898, in which the writer stated he had heard ‘Mr. Joseph Osborne, the ablest authority living on English