We can trace the physical resemblances of parents and children in the same family-- 'Sic oculos, sic ille manus, sic ora ferebat'; but scarcely less often the differences which distinguish children both from their parents and from one another.

We are told of similar mental peculiarities running in families, and again of a tendency, as in the animals, to revert to a common or original stock.

But we have a difficulty in distinguishing what is a true inheritance of genius or other qualities, and what is mere imitation or the result of similar circumstances.

Great men and great women have rarely had great fathers and mothers.

Nothing that we know of in the circumstances of their birth or lineage will explain their appearance.