[F5] Jupiter was a 37·5 inch “elk-nosed” pony, with a girth of 54·5 inches, rounded quarters, a low set-on tail, a complete set of chestnuts, wide open hoofs, and six inches of “bone.” _The Causes of the Dwarfing of Shetland Ponies._—Given sufficient food and shelter, horses up to 15 hands—the size of the tallest prehistoric Old World wild horse—can easily be bred and reared in both the Western and Northern Islands of Scotland. On the other hand, large breeds are soon dwarfed when, in addition to a limited supply of food, the conditions during a considerable part of the year are extremely unfavourable. If Shetland ponies have not sprung from a small wild pigmy race, it may be safely asserted that their small size is mainly due to isolation in small areas where they were forced to shift for themselves under, as a rule, extremely unfavourable conditions.[F6] Obviously the environment may play a double part. It may (1) arrest growth by failing to provide sufficient food and shelter, and (2) it may eliminate the individuals which, by growing beyond a certain size, require during times of stress more food and shelter than are available. Considerable stress has been laid by writers on the dwarfing influence of the surroundings. It is said, _e.g._, that “horses taken to the barren and cold islands of Shetland become gradually smaller and hardier, like ponies, and the hair becomes thicker and longer. Long-continued exposure to such conditions ultimately results in the production of an animal like the Shetland pony, small in size, extremely hardy, able to withstand the most severe winter climate, and to subsist on a minimum of food.”[F7] It might be said that this view is supported by experiments in the Western Islands. At the beginning of the eighteenth century the Captain of Clanranald (who was killed in 1715 at the battle of Sheriffmuir) brought from Spain “some Spanish horses which he settled in his principal island of South Uist. These in a considerable degree altered and improved the horses in that and the adjacent islands. Even in 1764, not only the form but the cool fearless temper of the Spanish horse could be discerned in the horses of that island.... These at that time, both in figure and disposition, were thought the best horses observed in the Highlands, and though of low stature were judged more valuable than any other horses of the same size.” The descendants of the Spanish horses introduced by Clanranald for a time increased the size of the horses in the adjacent islands. Nevertheless, in spite of the introduction of the Spanish horses at the beginning of the eighteenth century, and the introduction of many south-country horses during the second half of the eighteenth century, the Highland and Island horses at the beginning of the nineteenth century were “sometimes only 9 and seldom 12 hands high.” Moreover, though some of them were “of an excellent form,” with “great strength