ences of the parents on their progeny are readily observable in the hybrids of two highly contrasted "varieties," and especially where there are several young at a birth. In a litter of hybrid dogs, some may at maturity resemble the male and others the female, while some may be intermediate. These variations, in the respective potencies of the sexes in reproduction, can hardly be more clearly demonstrated than by the photographs of white and black oat plants and their hybrids, grown for the purpose of determining whether oats are naturally cross-fertilised (see plates, pp. 24, 25), by Mr Thomas Jamieson, F.I.C., Director of the Aberdeenshire Agricultural Research Association. These very interesting and instructive examples of variations in the respective reproductive potency of the sexes suggest a wide field for speculation on the processes of reproduction; but it is sufficient for our present purpose that they, as well as hybrid puppies, justify the inference that individual characteristics of two parents are not equally divided-not always at leastin their offspring, and also the assumption that where likeness to one parent preponderates, that individual has in similar proportion more of the blood of the parent it resembles than of the other, from which it differs in expression of type. This feature of heredity discloses one of Nature's methods - perhaps the most important after race hatred for maintaining purity of race, and it is the guide to success in selective breeding. As we have seen, the stock of hybrids, without intermixture of pure or nearly pure blood, disappears; but if the hybrid and its progeny are bred into the pure stock of either parent, the descendants have in two or three generations all the appearance of that race. This result will evidently be accelerated if such of the progeny as take after the race of one parent are bred into that race. And that is the practice in selective breeding. If a calf shows any strain of alien blood or inferiority in expression of type, it is destined to the butcher; and only if a bullcalf promises to become a higher expression of the type of its race than either parent, is it selected for improvement of the herd. Selective breeding thus co-operates with Nature, and thereby attains more promptly |