That the various breeds of sheep at present domesticated in Europe, have had a common origin, is not doubted by any zoologist, not withstanding the differences in their stature and proportions, the texture and colour of their wool, the presence or absence of horns, &c. The most marked deviation from the usual type is presented by a breed of Spanish sheep, distinguished by the length and straightness of the hair, and by the length and spiral twist of the horns. Various breeds are found in Asia and Africa, as to whose specific unity with each other, and with Eu ropean sheep, zoologists are not agreed. We have a remarkable example of climatic varia tion, however, in the fact, that in the races spread through Persia, Tartary, and China, the tail seems replaced by a double spherical mass of fat, which forms a most awkward excrescence on the rump, and is nearly desti tute of hair; whilst these sheep, transferred to the cold, dry pastures of Siberia, are affirmed by Ermann to lose this peculiar conformation in the course of a few generations. The sheep of Syria and Barbary, on the other hand, have an accumulation of fat in the tail itself, which is long, and sometimes attains a weight of from seventy to one hundred pounds. It is a curious and very significant fact, that the sheep of the Cape of Good Hope, which are descended from the European stocks, should exhibit the same tendency to the accumulation of fat about the rump, as is seen in the human races indigenous to that region. The sheep which were transported into South America by the Spaniards, have not multiplied so extensively as the oxen and swine ; and from their more limited diffusion, we find, as might be expected, that they ex hibit but a comparatively slight amount of variation. The remarkable change in the character of the hair, presented by the sheep in the West Indies has been already referred to. — Among sheep, as among other do mesticated animals, new races are continually being produced by breeders, not merely by crossing or intermixing races already con stituted and well known, but also by taking advantage of peculiarities which occasion ally present themselves spontaneously, and using means to perpetuate these. The fol lowing is oue of the most curious examples of this kind upon record. In the year 1791, a ewe on the farm of Seth Wright, in the state of Massachusetts, gave birth to a male lamb, which, without any known cause, had a longer body and shorter legs than the rest of the breed ; the joints also were peculiarly formed, and the fore-legs crooked. The con formation of this animal rendering it unable to leap over fences, it was thought desirable to endeavour to propagate its peculiarities ; and accordingly when it was fit for procreation, several ewes were impregnated by it. Out of the lambs first produced, only two presented the same peculiarities ; more were obtained in subsequent years ; and when they became capable of breeding with each other, the new race was completely established ; its distinc tive characters being uniformly presented when both parents possessed them, but tending to disappear when the sheep of the " ancon" or "otter" breed (as it is called) were allowed to breed with those of the ordinary type.* This fact, as we shall hereafter see, has an important bearing on the question of the spontaneous origination of permanent varieties, in the human or any other species that is disposed to undergo occasional modifications ; which modifications, under ordinary circum stances, disappear as often as they recur. Thus it is not uncommon to meet with fami lies distinguished by the possession of some peculiarity of feature, or by some well marked departure from the ordinary conformation, such as the possession of six fingers on each hand and six toes on each foot. If such were to intermarry exclusively with one another, there can be no reasonable doubt that the children would invariably exhibit the same peculiarity ; and that the six-fingered race, which now tends, whenever it is originated, to merge in the prevailing five-fingered type, would then become permanent. When it is considered that the influence of a scanty population, in the early ages of the world, by isolating different families from each other, and causing inter-marriages amongst even very near relatives, would have been precisely the same with that which is now exercised by the breeders of animals, we see one reason why the varieties which then arose should have had a much greater tendency to per petuation, than those which now occasionally present themselves.
In regard to the horse, it will be sufficient to observe that no zoologist has ever ex pressed any doubt of the specific unity of all the domesticated breeds, or of their identity of origin with the so called " wild horses" of Northern Asia : which are probably descended from domesticated progenitors. Yet their
diversities in stature, conformation, &c. are very considerable. Thus the ordinary height of the Shetland pony is from eight to ten hands ; and individuals have been occasionally seen which were no more than seven. On the other hand, the draught horse commonly stands from sixteen to seventeen hands ; and not unfrequently surpasses this height. In regard to the conformation of the skull, again, it has been remarked by Blumenbach, that there is more difference between the elon gated head of the Neapolitan horse and the skull of the Hungarian breed, which last is re markable for its shortness and the breadth of the lower jaw, than there is between the most dissimilar human crania. The differences in general constitution, also, as regards the power of sustained effort on the one hand, or of intense exertion for a short period on the other, are no less remarkable. But the breeds which are furthest removed from each other in these particulars are connected by such a gradual series of transitional forms, that there is no possibility of drawing a line between them ; and, like the various races of dogs, sheep, &c., they freely inter mingle with each other, and produce offspring which are as fertile with their own kind, as with either of the parent stocks. It has been, in fact, by such intermixture of the large and powerful races of Northern Asia with the lighter and more agile horses of Arabia and Barbary, that many of the Euro pean breeds have been obtained. The wild horses which at present range over the plains of Tartary differ from the domesticated races in several particulars ; thus, as we are in formed by Pallas, the cranium is relatively larger and more vaulted, the limbs are stronger, the back is less arched ; their hoofs are smaller and more pointed ; their ears are longer and bent more forward. Their habits, moreover, are peculiar; for they asso ciate together in herds or troops to the number of several thousands, spreading abroad to feed, but congregating together on the appearance of danger, and seemingly putting themselves under the direction of a leader ; on the approach of an enemy they close into a dense crowd, and, attacking the intruder, trample him to death ; or, like many other gregarious animals, the females, the young, and the weak being placed in the rear, the stronger individuals array themselves in front, and fight most vigorously with their heels. Now these peculiarities of structure and habit are not only seen in the wild horses of Northern Asia, but also in those which have spread themselves over the extensive plains of South America, since their introduction into that continent by the Spaniards ; and it is nearly certain that the former, like the latter, are the descendants of a domesticated stock, whose return to something like the original condition of the species, has repro duced (at least in some degree) the original instincts, which had been entirely subdued for a time by the influence of domestication. In the horse, as in the dog, we have evidence that the habits which are developed by human training may become, to a certain extent, hereditary. Thus, it is observed that the wild horse has no pace but the walk and the gallop; the trot, to which European horses are usually trained, is an acquired habit, yet it obviously "comes naturally" to the colt of a domesticated breed ; and, in like manner, the peculiar pace to which the South Ame rican horses are trained (which is a kind of running amble, the two legs of the same side being moved forwards together) is used with out any instruction by the offspring of those by whom it has been acquired. Another ex ample of the transmission of acquired pro pensities in horses is mentioned by Mr. Knight: the Norwegian ponies have been taught to obey the voice of their riders rather than the bridle ; and the English horse-breakers com plain that it is impossible to produce the latter habit in the offspring•of this race placed under their tuition, notwithstanding that they are exceedingly docile and obedient when they understand the commands of their master, as imparted by word of mouth. It is equally difficult, he adds, to keep them within hedges, owing, perhaps, to the unrestrained liberty to which the race may have been accustomed in Norway.