These organs are now no longer useful, but they once were so, and were therefore once purposive, though not so now. They are the expressions of a bygone usefulness; sayings, as it were, about which there was at one time infinite wrangling, as to what both the meaning and the expression should best be, so that they then had living significance in the mouths of those who used them, though they have become such mere shibboleths and cant formulae to ourselves that we think no more of their meaning than we do of Julius Caesar in the month of July. They continue to be reproduced through the force of habit, and through indisposition to get out of any familiar groove of action until it becomes too unpleasant for us to remain in it any longer. It has long been felt that embryology and rudimentary structures indicated community of descent. Dr. Darwin and Lamarck insisted on this, as have all subsequent writers on evolution; but the explanation of why and how the structures come to be repeated--namely, that they are simply examples of the force of habit--can only be perceived intelligently by those who admit so much unity between parents and offspring that the self-development of the latter can be properly called habitual (as being a repetition of an act by one and the same individual), and can only be fully sympathized with by those who recognize that if habit be admitted as the key to the fact at all, the unconscious manner in which the habit comes to be repeated is only of a piece with all our other observations concerning habit. For the fuller development of the foregoing, I must refer the reader to my work 'Life and Habit.'