We have seen that maintaining life, expressed in physical terms, is maintaining a balanced combination of internal actions in face of external forces tending to overthrow it; and we have seen that advance toward a higher life, has been an acquirement of ability to maintain the balance for a longer period, by the successive additions of organic appliances which by their actions counteract, more and more fully, the disturbing forces. Here, then, we are led to the conclusion that the life called moral is one in which this maintenance of the moving equilibrium reaches completeness, or approaches most nearly to completeness. This truth is clearly disclosed on observing how those physiological rhythms which vaguely show themselves when organization begins, become more regular, as well as more various in their kinds, as organization advances. Periodicity is but feebly marked in the actions, inner and outer, of the rudest types. Where life is low there is passive dependence on the accidents of the environment; and this entails great irregularities in the vital processes. The taking in of food by a polype is at intervals now short, now very long, as circumstances determine; and the utilization of it is by a slow dispersion of the absorbed part through the tissues, aided only by the irregular movements of the creature's body; while, such æration as is effected is similarly without a trace of rhythm. Much higher up we still find very imperfect periodicities; as in the inferior molluscs which, though possessed of vascular systems, have no proper circulation, but merely a slow movement of the crude blood, now in one direction through the vessels and then, after a pause, in the opposite direction. Only with well-developed structures do there come a rhythmical pulse and a rhythm of the respiratory actions. And then in birds and mammals, along with great rapidity and regularity in these essential rhythms, and along with a consequently great vital activity and therefore great expenditure, comparative regularity in the rhythm of the alimentary actions is established, as well as in the rhythm of activity and rest; since the rapid waste to which rapid pulsation and respiration are instrumental, necessitates tolerably regular supplies of nutriment, as well as recurring intervals of sleep during which repair may overtake waste. And from these stages the moving equilibrium characterized by such interdependent rhythms, is continually made better by the counteracting of more and more of those actions which tend to perturb it.