2d. That while this may be caused for the most part, by the very fact of crossing, yet it is principally due to the superior influence of the male over the size and external appearance of the offspring; so that it is desirable, for the purpose of the butcher, that the male should be of a larger frame than the female, and should excel in those peculiarities we are desirous of reproducing. Let it be here however, repeated, as an exceptional truth, that though as a rule the male parent influences mostly the size and external form, and the female parent the constitution, general health and vital powers, yet that the opposite result sometimes takes place.
3d. Certain peculiarities may be imparted to a breed by a single cross. Thus, the ponies of the New Forest exhibit characteristics of blood, although it is many years since that a thorough-bred horse was turned into the forest for the purpose. So, likewise, we observe in the Hampshire sheep the Roman nose and large heads, which formed so strong a feature in their maternal ancestors, although successive crosses of the South Down were employed to change the character of the breed. * * *
4th. Although in the crossing of sheep for the purpose of the butcher, it is generally advisable to use males of a larger breed, provided they possess a disposition to fatten; yet, in such cases, it is of importance that the pelvis of the female should be wide and capacious, so that no injury should arise in lambing, in consequence of the increased size of the heads of the lambs. The shape of the ram's head should be studied for the same reason. In crossing, however, for the purpose of establishing a new breed, the size of the male must give way to other more important considerations; although it will still be desirable to use a large female of the breed which we seek to improve. Thus the South Downs have vastly improved the larger Hampshires, and the Leicester the huge Lincolns and the Cotswolds.
5th. Although the benefits are most evident in the first cross, after which, from pairing the cross-bred animals, the defects of one breed or the other, or the incongruities of both, are perpetually breaking out—yet, unless the characteristics and conformation of the two breeds are altogether averse to each other, nature opposes no barrier to their successful admixture; so that in the course of time, by the aid of selection and careful weeding, it is practicable to establish a new breed altogether. This, in fact, has been the history of our principal breeds. * * *
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.
Such was in all probability the origin of the celebrated horse Justin Morgan; an animal which not only did more to stamp excellence and impart value to the roadsters of New England than any other, but was the originator of the only distinct, indigenous breed of animals of which America can boast;—a breed which as fast and durable road horses and for any light harness work, is not equalled by any other, any where. In the present state of our knowledge it is scarcely conceivable how an animal possessing the endowments of Justin Morgan could have originated in any other way than from such a parentage as above indicated. On the other hand it is very certain that contrast in character, as well as in breed, has occasioned much of the disappointment of which breeders have had occasion to complain.
The principle here laid down is one of broad application, and should never be lost sight of in attempts at improvement by crossing. Another point worthy special attention is that all crossing, to insure successful results, should be gentle rather than violent; that is, never couple animals possessing marked dissimilarity, but endeavor to remedy faults and to effect improvement by gradual approaches. Harmony of structure and a proper balancing of desirable characteristics, "an equilibrium of good qualities," as it has been happily expressed, can be secured only in this way.