The lesson taught by the law of atavism is very plain. It shows the importance of seeking "thorough-bred" or "well-bred" animals; and by these terms are simply meant such as are descended from a line of ancestors in which for many generations the desirable forms, qualities and characteristics have been _uniformly shown_. In such a case, even if ancestral influence does come in play, no material difference appears in the offspring, the ancestors being all essentially alike. From this stand point we best perceive in what consists the money value of a good "pedigree." It is in the evidence which it brings that the animal is descended from a line all the individuals of which were alike, and excellent of their kind, and so is almost sure to transmit like excellencies to its progeny in turn;--not that every animal with a long pedigree full of high-sounding names is necessarily of great value as a breeder, for in every race or breed, as we have seen while speaking of the law of variation, there will be here and there some which are less perfect and symmetrical of their kind than others; and if such be bred from, they may likely enough transmit undesirable points; and if they be mated with others possessing similar failings, they are almost sure to deteriorate very considerably. Pedigree is valuable in proportion as it shows an animal to be descended, not only from such as are purely of its own race or breed, but also from such individuals in that breed as were specially noted for the excellencies for which that particular breed is esteemed. Weeds are none the less worthless because they appear among a crop consisting chiefly of valuable plants, nor should deformed or degenerate plants, although they be true to their kind, ever be employed to produce seed. If we would have good cabbages or turnips, it is needful to select the most perfect and the soundest to grow seed from, and to continue such selection year after year. Precisely the same rule holds with regard to animals. The pertinacity with which hereditary traits cling to the organization in a latent, masked or undeveloped condition for long after they might be supposed to be wholly "bred out" is sometimes very remarkable. What is known among breeders of Short-horns as the "Galloway alloy," although originating by the employment for only once of a single animal of a different breed, is said to be traceable even now, after many years, in the occasional development of a "smutty nose" in descendants of that family.