(69.) _Changes produced by Climate._--The wonderful power of temperature in effecting changes upon animals, is well illustrated by the Portuguese, who, after a residence of three hundred years in India, are said to be at present almost as black as Caffres. Bishop Heber, speaking of India, says, "It is remarkable to observe how surely all these classes of men (whites--Persians, Greeks, Tartars, Turks, and Arabians), in a few generations, even without any inter-marriage with the Hindoos, assume the deep olive tint, little less dark than a negro, which seems natural to the climate." Buchanan also in his travels through the same country, alludes to a tribe of black Jews who have, in all probability, been settled in the district ever since the period of the captivity under Nebuchadnezzar, 3000 years ago, and who retain all the national peculiarities of their race, with the exception of their colour, which is now as dark as that of the surrounding tribes. These examples, however, it may be affirmed, are not to the point, as embracing theories in regard to peculiar changes in an animal different from the sheep, but such objections are perfectly groundless, as what will affect colour in mankind, will lead to changes even of a more wonderful nature in the sheep, seeing that it is abandoned more entirely to such an influence. (70.) _Temperature preferred by Sheep._--Sheep, though capable of thriving in a great variety of climates, seem to prefer such as are temperate, and in these only do they arrive at perfection. They are common on the Cordilleras at an elevation of from 3300 to 8200 feet, within which limits they propagate readily without any care; but the reverse is the case in hotter regions, it being difficult to rear lambs in the plains of Meta, and no sheep are to be met with from the river to the foot of the Cordilleras, though their skins, from being in demand for making parchment, sell as high as those of the ox. Sheep were at one time, according to Thunberg, the scarcest articles in Batavia, as their woolly coat rendered the heat of the climate quite insupportable; but this inconvenience was at last remedied by sending them, on their arrival from the Cape, further up the country, to the Blue Mountains, where the air is several degrees colder. The question then naturally occurs, if an elevation of temperature is, as in this instance, fatal to these animals, how do they happen to have spread over a vast tract of country in spite of such extremes? Simply for the reason, that when an animal is left to the exercise of its own free will, and the dominion of its instincts, it will not subject itself to the danger of an extreme in any thing. It will not traverse several hundred miles in a single season, and thus expose itself to sudden changes. The natural dispersion of all animals is gradual, so that their constitutions are enabled, from the slowness of the transition, to accommodate themselves, by an alteration in covering and habit, to