Two distinct lives combined in the animal—Characters of the apparatus of the organic life—Characters of the apparatus of the animal life—Characteristic differences in the action of each—Progress of life—Progress of death. Of the two sets of functions carried on by living beings, it has been shown, that the plant performs only one, while the animal exercises both. The two lives thus in continual play in the animal differ from each other as much as the process of vegetation differs from that of thought, yet they are united so closely, and act so harmoniously, that their existence as distinct states is not only not apparent to ordinary observation, but the very discovery of the fact is of recent date, and forms one among the splendid triumphs of modern physiology. Their action is perfect, yet their separate identity is so distinctly preserved, that each has its own apparatus and its own action, which are not only not the same, but, in many interesting circumstances, are in striking contrast to each other. 1. In general the organs that belong to the apparatus of the organic life are single, and not symmetrical; the organs that belong to the apparatus of the animal life are either double, or symmetrical, or both. As will be shown hereafter, the heart, the lungs, the stomach, the intestines, the liver, the pancreas, the spleen, the instruments by which the most important functions of the organic life are carried on, are single organs. (Chap. 5.) The figure of each is more or less irregular, so that if a line were carried through their centre, it would not divide them into two equal and precisely corresponding portions. On the contrary, the organs of the animal life are symmetrical. The brain and the spinal cord are divisible into two perfectly equal parts. (Chap. 5.) The nerves which go off from these organs for the most part go off in pairs equal in size and similar in distribution. (Ibid.) The trunk, so important an instrument of voluntary motion, when well formed, is divisible into two perfectly corresponding portions. (Ibid.) The muscular apparatus of one half of the body is the exact counterpart of that of the other; while the arms, the hands, and the lower extremities are not only double, but the organization of the one is precisely similar to that of its fellow.