The so-called mother of the child isn't the child's begetter, but only a sort of nursing soil for the new-sown seed. The man, the one on top, is the true parent, while she, a stranger, foster's a stranger's sprout.
Alas for the affairs of men! When they are fortunate you might compare them to a shadow; and if they are unfortunate, a wet sponge with one dash wipes the picture away.