Series II
A comma isolates vocatives and incidental clauses.
—"Cæsar, let your men go forward," said the guide.
—Why do you want to find your father, Mora?
—"No," said he, "I shall be very well presently."
—"Boys," said our host, "I know whose hand it is."
—That, excuse me for saying so, is not the way to speak to a friend.
—"Come with us, you handsome young huntsman," he cried.
Series III
A comma separates clauses, especially for clearness, when the elements of one clause might seem to apply equally well to another clause, and when one clause is interpolated between the essential elements of another.