only plentiful materials from which to select, but the keenest discrimination. After the breeder has successfully established his flock, and given them an excellent character, he soon encounters a serious evil. He must "breed in-and-in," as it is called--that is, interbreed between animals more or less nearly related in blood--or he must seek rams from other flocks, at the risk of losing or changing the distinctive character of his flock, hitherto so carefully sought, and built up with so much painstaking. The opponents of in-and-in breeding contend that it renders diseases and all other defects hereditary, and that it tends to decrease of size, debility, and a general breaking up of the constitution. Its defenders, on the other hand, insist that, if the parents are perfectly healthy, this mode does not, of itself, tend to any diminution of healthfulness in the offspring; and they likewise claim--which must be conceded--that it enables the skilful breeder much more rapidly to bring his flock to a particular standard or model, and to keep it there much more easily--unless it be true that, in course of time, they will dwindle and grow feeble. [Illustration: THE SCOTCH SHEEP-DOG, OR COLLEY.] So far as the effect on the constitution is concerned, both positions may be, to a certain extent, true. But it is, perhaps, difficult always to decide with certainty when an animal is not only free from disease, but from all tendency or predisposition towards it. A brother or sister may be apparently healthy--may be actually so--but may still possess a peculiarity of individual conformation which, under certain circumstances, will manifest itself. If these circumstances do not chance to occur, they may live until old age, apparently possessing a robust constitution. If tried together, their offspring--by a rule already laid down--will possess this individual tendency in a double degree. If the ram be interbred with sisters, half-sisters, daughters, granddaughters, etc., for several generations, the predisposition toward a particular disease--in the first place slight, now strong, and constantly growing stronger--will pervade, and become radically incorporated into, the constitution of the whole flock. The first time the requisite exciting causes are brought to bear, the disease breaks out, and, under such circumstances, with peculiar severity and malignancy. If it be of a fatal character, the flock is rapidly swept away; if not, it becomes chronic, or periodical at frequently recurring intervals. The same remarks apply, in part, to those defects of the outward form which do not at first, from their slightness, attract the notice of the ordinary breeder. They are rapidly increased until, almost before thought of by the owner, they destroy the value of the sheep. That such are the common effects of in-and-in breeding, with such skill as it is commonly conducted, all know who have given attention to the