Attention may here be drawn to a peculiar and remarkable mode of influence. If a pure-bred mare have foals by an ill-bred sire, they will be ill-bred. This we can readily understand. But if she subsequently have a foal by a perfectly well-bred sire, that foal, too, may in some cases be tainted by the blemish of the previous sire. So, too, with dogs. If a pure-bred bitch once produce a mongrel litter, no matter how carefully she be subsequently matched, she will have a tendency to give birth to pups with a mongrel taint. This subsequent influence of a previous sire is a puzzling fact. It may be that some of the male germ-nuclei are absorbed, and influence the germ-cells of the ovary. But this seems an improbable solution of the problem. It is more likely, perhaps, that in the close relation of mother and f[oe]tus during gestation, each influences the other (how it is difficult to say). On this view the bitch retains the influence of the mongrel puppies--is herself, in fact, partially mongrelized--and therefore mongrelizes subsequent litters. It would not be safe, however, to base any far-reaching conclusions on so peculiar a case, the explanation of which is so difficult. At all events, it is impossible to exclude the possibility of direct action on the germ, though the _particular_ nature of the results of such influence are noteworthy. We may pass now to the evidence that has been adduced in favour of a cumulative effect in the exercise of function, or of the inheritance of the results of use or disuse. Here, again, it must be remembered that no one questions the effects of use and disuse in the individual. What we seek is convincing evidence that such effects are inherited. Physiologically, the effects of use or disuse are, in the main, effects on the relative nutrition, and hence on the differential growth of organs. When an organ is well exercised, there is increased nutrition and increased growth of tissue, muscular, nervous, glandular, or other. When an organ is, so to speak, neglected, there is diminished blood-supply, diminished growth, and diminished functional power. The development of a complex activity would necessitate a complex adjustment of size and efficiency of parts, involving a nice balance of differential growth dependent on delicately regulated nutrition. What is the evidence that adjusted nutrition can be inherited?