(73.) _Causes of the various forms of the Horn._--Horns are seldom met with in the sheep of hot climates, occurring more frequently in cold and temperate regions; thus following closely the development of the other coverings, to which, as before stated (19), they are strictly analogous. The fleece consists of two portions--hair and wool, the one predominating more or less over the other, as the climate may direct. The form of the horns is always in unison with the character of the fleece: thus, if the animal is covered with hair, as in the goat, the horns will be straight; but if it is clothed with wool, as in the sheep, the horns will be curved. The same holds good in other animals. The reason of this appears to lie in the tendency which the hair or wool, constituting the horny sheath, has to model the form of the supporting bone. The fibre of hair is nearly straight; that of wool is, on the other hand, remarkable for the number of tufted curls, or small spiral ringlets, into which it naturally contracts; so that a Merino ram, for example, will never be found with rectilinear horns, nor a true goat with twisted ones. The truth of these remarks is borne out by observations on animals on whose heads more than two horns are occasionally met with. We always in such instances notice, that the additional horns are straight, thus indicating the presence of a considerable quantity of hair among the wool. The curve will be more decided, and the twists more numerous, in proportion as the fibre comes nearer and nearer to a perfect wool--evidence of which we have in the beautifully-tufted and spiral horns of the Merino ram, which are as opposite in this respect to those of the goat, as is its fleece to the hairy coat of the latter. From these considerations I am led to believe, that the form of the horn, when present, is an excellent guide to the nature and quality of the other coverings, and an index to every gradation which can possibly occur between wool and hair.