We confess that we cannot entirely admit either of the antagonistic doctrines held by the rival advocates of crossing and pure breeding. The public have reason to be grateful to the exertions of either party; and still more have they respectively reason to be grateful to each other. * * * * Let us conclude by repeating the advice that, when equal advantages can be attained by keeping a pure breed of sheep, such pure breed should unquestionably be preferred; and that, although crossing for the purpose of the butcher may be practiced with impunity, and even with advantage, yet no one should do so for the purpose of establishing a new breed, unless he has clear and well defined views of the object he seeks to accomplish, and has duly studied the principles on which it can be carried out, and is determined to bestow for the space of half a life-time his constant and unremitting attention to the discovery and removal of defects." The term crossing is sometimes used in a much more restricted sense, as in the remark of Mr. Boswell in his essay quoted on page 69 where he says, "When I praise the advantage of crossing I would have it clearly understood that it is only to bring together animals _not nearly related_ but always of _the same breed_." It is evident that such crossing as this is wholly unobjectionable; no one but an avowed and ultra advocate of close breeding could possibly find any fault with it. There is yet another style of crossing which when practicable, may, it is believed, be made a means to the highest degree of improvement attainable, and especially in the breeding of horses. The word "breed" is often used with varying signification. In order to be understood, let me premise that I use it here simply to designate a class of animals possessing a good degree of uniformity growing out of the fact of a common origin and of their having been reared under similar conditions. The method proposed is to unite animals _possessing similarity of desirable characteristics, with difference of breed_; that is to say, difference of breed in the sense just specified. From unions based upon this principle, the selections being guided by a skillful judgment and a discriminating tact, we may expect progeny possessing not only a fitting and symmetrical development of the locomotive system, but also an amount and intensity of nervous energy and power unattainable by any other method.