(75.) _Geographical limits of the Sheep._--Every plant and animal has certain geographical limits, out of which it cannot exist. With the exception of man and the dog, no animal has a wider range than the sheep, extending as it does from Iceland almost to the equator, and from a few degrees south of that to the polar extremity of South America. But though existing under so great a variety of exposures, it must not be inferred that it can come to perfection in them all. On the contrary, it rather delights in the temperate zones, and can evidently only be raised to its highest point of excellence in the countries of the vine. The western parts of continents produce better sheep than the eastern, and the southern hemisphere better than the northern; as in the former situations the temperature is more nearly equable than in the latter. The same may be said of maritime districts, as compared with such as are inland. Temperature is affected in the same way by elevation as by northern or southern position--the mean heat diminishing in the same ratio when ascending a mountain, as in receding from the equator. On this account, Humboldt compared the earth to two mountains with their bases at the equator, and their summits at the poles. The mean temperature, when resulting from the height of the place above the level of the sea, is at the same time influenced by the nature of the aspect, as we notice in the Alps, where the Glacier exists on the northern side, at the same elevation at which the vineyard yields a perfect fruit upon the southern. (76.) _Particular forms induced by certain limits._--The character which a predominance of heat, or cold, impresses on the animal as a whole, extends also to individual parts of the body. The sheep of South Africa are, as all the world know, remarkable for the magnitude of the tail, which forms an immense fatty appendage. The sheep of Persia, Tartary, and China, are distinguished from all others by the tail forming a _double globe_ of fat. The North of Europe, and North of Asia, are overrun by a breed in which the tail is almost wanting, while that of Southern Russia, India, and Guinea, stands pre-eminent from the elongation of the tail, and, in respect to that of the two last named places, also of the legs.